Cataract

Extracapsular cataract surgery with intraocular lens (IOL) implantation is usually well tolerated in advanced diabetic retinopathy, when there are no anterior segment neovascularizations.^17,18 The removal of an opacified lens allows for a better fundus evaluation and visualization, e.g. for panretinal photocoagulation. In the past, higher incidences of iris neovascularizations, secondary glaucoma, and vitreous hemorrhage were reported after intracapsular cataract extraction in proliferative diabetic retinopathy, notably by Aiello et al.¹⁹ However, in recent times, as small incision cataract surgery, photocoagulation, and anti-VEGF drugs are widely used, anxiety has shifted from iris neovascularizations to diabetic macular edema. Progression may be lower when grid/focal lasers are applied before cataract surgery, or when panretinal photocoagulation is applied after lens extraction instead of before.²⁰ Today, proliferative diabetic retinopathy should be treated with panretinal photocoagulation before cataract surgery whenever possible, but panretinal photocoagulation may also be applied at time of surgery or shortly thereafter.²¹ Along with improvements in vitrectomy surgery techniques, an increasing trend for simultaneous vitrectomy and cataract surgery has been observed in the past decades; lensectomy may be considered in revision vitrectomy surgery or in eyes with much reduced prognosis.^22,23 The advantage of any cataract extraction is a better intraoperative view and access to the vitreous base, which is of upmost importance in cases of fibrovascular proliferations in diabetic retinopathy or proliferative vitreoretinopathy; there is also evidence from Schiff et al. that reoperation rates seem to decrease when the lens has been removed during vitrectomy.²⁴ Similarly, fear of iris neovascularizations after combined surgery has been reduced by careful application of panretinal photocoagulation and anti-VEGF drugs during surgery.²⁴ In younger patients with clear lenses, the loss of accommodation has to be weighed against possible intra- and postoperative complications, such as earlier cataract formation needing another surgery.^17,24

High-risk retinal neovascularization

Fibrovascular proliferations

Severe fibrovascular proliferations in proliferative diabetic retinopathy can produce a major threat of profound loss of vision without surgical intervention. A progressive proliferation of fibrovascular preretinal tissue may occur, despite panretinal photocoagulation, as described by Hutton, Smiddy, and Ho (Figs 111.1–111.3).^17,18,25

Fig. 111.1 Proliferative diabetic retinopathy with extensive neovascularizations.

Fig. 111.2 Progression of fibrovascular proliferation and vitreous hemorrhage despite panretinal photocoagulation.

Fig. 111.3 Postoperative appearance after vitrectomy for severe fibrovascular proliferation.

The Diabetic Retinopathy Vitrectomy Study (DRVS)^26,27 formed the definition of “advanced, active, neovascular or fibrovascular proliferation” based on a review of studies of the natural history. The term “severe” for new vessels or fibrovascular proliferations was defined in the DRVS according to standard photographs and size definitions.²⁶ Basically, the benefit of surgery tends to increase with increasing severity of neovascularization. Eyes most suitable for early vitrectomy are those with both severe fibrovascular proliferations and at least moderately severe neovascularizations despite extensive panretinal photocoagulation.^6,27 More recent papers reported similar favorable surgical results for severe diabetic fibrovascular proliferations.

Stable or improved visual function may be achieved in 78% of cases on average. Good prognostic factors include younger age at baseline (<40 years), preoperative panretinal photocoagulation, better visual acuity (>5/200), no iris neovascularizations, and no iatrogenic breaks at surgery.^26,28 Therefore, extensive panretinal photocoagulation is recommended prior to early vitrectomy to improve the patient’s outcome.^25,29–31 In patients with relatively asymptomatic pathologies, intensive counseling is essential, as some eyes lose vision despite careful surgery.

Vitreous hemorrhage

Nonclearing vitreous hemorrhage in diabetic retinopathy was the earliest indication for vitrectomy in the 1970s, representing 70% of cases at that time.² Today, it is still one of the most common indications for vitrectomy, although surgery may be avoided or at least postponed in many cases. Waiting, head elevation or intravitreal injection of hyaluronidase may lead to spontaneous blood clearing, thus allowing for panretinal photocoagulation to induce regression of active retinal neovascularizations.^32,33 Diode or krypton laser systems, eventually delivered by indirect ophthalmoscopy might be more effective than argon laser in some cases.²⁵ Early vitrectomy, defined by the DRVS as within 1–4 months from onset, results in earlier recovery of vision and better functional outcome after 2 and 4 years.²⁷ The benefit is greater in patients with type 1 diabetes mellitus, compared to type 2. This difference might be influenced by a greater incidence of maculopathy and posterior vitreous detachment in elderly type 2 diabetic patients.³⁴

In proliferative diabetic retinopathy with dense premacular (subhyaloidal) vitreous hemorrhage, blood is trapped between the posterior hyaloid interface and the internal limiting membrane. The hemorrhage is usually well demarcated, resulting in massive visual loss. It may be associated with fibrovascular proliferations, preretinal membrane formation or tractional macular detachment, which are common indications for an early vitrectomy (Figs 111.4, 111.5).²⁶ Less-invasive treatment methods include observation, laser membranotomy, or intravitreal injections with recombinant tissue plasminogen activator (r-tPA) or gas. When those methods are not successful, vitrectomy may improve functional recovery or decrease the risk of complications.^26,30,35 Again, a longer delay than a few months for surgery is not recommended, as surgical dissection may become more difficult^25,36 if the disease progresses. Another relatively urgent indication for vitrectomy in nonclearing vitreous hemorrhage is rubeosis iridis and/or severe progressive proliferation of the fellow eye, especially when no panretinal photocoagulation has been applied before.^25,27

Fig. 111.4 Dense premacular hemorrhage. Note extensive fibrovascular proliferation, contraction and distortion of retinal vessels.

Fig. 111.5 Postoperative appearance after vitrectomy, membranectomy, and removal of preretinal hemorrhage.

Macular traction and macular edema

Vitreomacular traction syndrome, vitreopapillary traction, diabetic macular edema, epiretinal membrane or macular hole formation in patients with proliferative diabetic retinopathy do have specific features in their presentation and management, representing relatively new indications for vitrectomy.^37–41 Opacification of posterior vitreous cortex or preretinal membrane formation alone results in substantial visual loss, sometimes associated with metamorphopsia or diplopia.^29,42 These changes may occur after premacular hemorrhage or extensive panretinal photocoagulation.²⁶ Vitreomacular traction may be associated with more complex vitreoretinal adhesions than in nondiabetic patients, eventually resulting in tractional retinoschisis.⁴³ Vitreopapillary traction is a relatively new, controversial indication for vitrectomy, with limited evidence for functional improvement.⁴⁴ In eyes with coexistent macular edema, a causative role of vitreopapillary traction has been suggested. Diabetic epiretinal membranes are more likely to have focal attachments to the macula and more proliferative activity than idiopathic epiretinal membranes.^39,40 In cases of diabetic macular edema, tangential traction or former intravitreal surgery, macular holes may develop.^37,38,45 To avoid progression of diabetic macular edema, panretinal photocoagulation may be divided into smaller sessions or be applied after intravitreal injections of anti-VEGF drugs.^46,47

All these pathologies are indicative for an early, extensive and careful surgical treatment, usually vitrectomy combined with central membrane peeling.⁴⁸ Generally, the functional outcome is negatively associated with preoperative visual acuity and the degree of maculopathy.^37,49

Retinal detachment

Tractional retinal detachment

As neovascular membranes in proliferative diabetic retinopathy grow within the cortical vitreous gel, they may produce firm vitreoretinal adhesions and contract over time,^41,50 resulting in tractional retinal detachment.⁵¹ Diabetic tractional macular detachment therefore has been the most common indication for vitrectomy.²⁵ However, the management of peripheral retinal tractional detachment seems to have changed in recent times. Traditionally, those cases were observed for a while as the risk of complicated vitrectomy seemed to exceed the low progression rates.⁵² As anatomic and functional results after vitrectomy have substantially improved, an earlier surgical approach in cases with peripheral tractional detachment seems reasonable.^53,54 Moreover, functional results after successful vitrectomy in severe macular tractional detachment are still poor (Figs 111.6, 111.7).⁵⁴ Also, chronic cases of diabetic tractional detachment may be a lesser indication for surgery, as the retina under tractional fibrovascular proliferations usually becomes atrophic.^6,18,54 In general, vitrectomy reoperation rates in diabetic tractional detachment are between 24% and 47%.^55–57

Fig. 111.6 Tractional retinal detachment involving the entire macula. This patient had severe fibrovascular proliferation and traction along the arcades with recent extension of the detachment to involve the macula.

Fig. 111.7 Postoperative appearance after vitrectomy, membranectomy, and retinal reattachment.

Factors with a more favorable outcome in the literature are: age <50 years, preoperative panretinal photocoagulation; visual acuity >5/200; no or few iris neovascularizations or retinal proliferations; macular detachments <30 days, and no iatrogenic breaks.^6,25,58

Combined tractional–rhegmatogenous retinal detachment

Severe fibrovascular proliferations in proliferative diabetic retinopathy may cause progressive traction and membrane contraction combined with posterior retinal breaks. The shape of the retina appears convex in contrast to tractional detachment, and the dimension of detachment is often greater, extending over the ora serrata.^41,59,60 The retinal surface often shows white hydration lines, which are diagnostic of retinal holes. The holes are often small, located posteriorly, paravascular or immediately adjacent to vitreoretinal tractions and retinal elevations.^60,61 Sometimes, subretinal hemorrhage may be present.⁶² Vitrectomy combined with silicone oil tamponade is frequently indicated in particularly severe cases, especially when the second eye shows a poor visual function (Figs 111.8, 111.9).^60,63 Reports of silicone oil surgery generally show a high rate of reattachments with just a moderate chance of functional improvements (see below). Silicone oil finally helps to reduce the incidence of further complications, as neovascular glaucoma and phthisis in those desperate cases.^60,63

Fig. 111.8 Combined tractional–rhegmatogenous detachment with dense fibrovascular proliferations over optic nerve and arcades after tractional retinoschisis.

Fig. 111.9 Postoperative appearance after successful vitrectomy, membranectomy, endophotocoagulation, and silicone oil tamponade/removal.

Neovascular glaucoma

Neovascular glaucoma is a very severe complication in proliferative diabetic retinopathy. It is assumed that the ischemic retina is the source of vasoproliferative growth factors that may diffuse into the anterior segment. Consequently, growth of neovascularizations and fibrovascular membranes in the chamber angle obstruct aqueous outflow and intraocular pressure rises; different stages of neovascular glaucoma have been described.^64,65 Therefore, the first therapeutic target should be the cause of the neovascular stimulus, indicating extensive panretinal photocoagulation or cryotherapy.⁶⁶ Intravitreal or intracameral anti-VEGF medications, such as bevacizumab, may be helpful as short-term adjunct to panretinal photocoagulation or when panretinal photocoagulation fails to cause regression of rubeosis.^67–69 This treatment alone usually induces regression of neovascularizations, however, fibrovascular proliferations in the chamber angle may contract and the pressure remains high.⁵⁹

In cases of opaque optical media, as vitreous hemorrhage or cataract, controlled panretinal photocoagulation can only be performed after vitrectomy and/or cataract extraction, which has been shown to reduce rubeosis and improve neovascular glaucoma.^70,71 In addition, silicone oil tamponade prevents recurrent vitreous hemorrhage and may induce regression of rubeosis.⁷²

Vitrectomy may be combined with endocyclophotocoagulation of ciliary processes or partial retinectomy to improve perfusion and reduce intraocular pressure.^73,74 Patients with higher stage neovascular glaucoma with synechial angle closure almost always need some sort of glaucoma surgery.

Filtering surgery in diabetic neovascular glaucoma has significantly lower success rates than surgery for primary or secondary open-angle glaucoma.⁷⁵

The intraoperative use of antimetabolites, such as 5-fluorouracil and mitomycin C, is strongly recommended; in addition, intensive perioperative anti-inflammatory and antiproliferative treatments, as well as anti-VEGF injections and panretinal photocoagulation can improve the outcome.^68,76

The implantation of glaucoma-drainage tubes (as Molteno, Baerveldt or Ahmed implants) is also very common, although the drainage capacity can be compromised by epibulbar scarring or recurrent intracameral or intravitreal haemorrhages.^77,78 Nonpenetrating glaucoma surgery, as well as argon laser trabeculoplasty, is generally not recommended in diabetic neovascular glaucoma, as angle closure due to the rubeotic process can deteriorate postoperatively.⁷⁵

Additional vitrectomy surgery should be considered at earlier stages of proliferative diabetic retinopathy and not only be reserved for advanced neovascular glaucoma.⁷⁹ It should be combined with panretinal photocoagulation ab interno; in addition, a pars-plana glaucoma drainage implant may be considered to stabilize the glaucoma.⁷⁷

Cyclodestruction, as transscleral cryo- or diode-laser cyclocoagulation, is a helpful, widely used method in advanced neovascular glaucoma. However, this treatment is usually reserved for eyes with low visual function at presentation.^80,81 Blind, painful eyes may still need retrobulbar alcohol injections or, in the worst case, evisceration or enucleation.⁸²

Education and training

Surgery for complications of diabetic retinopathy, notably vitrectomy, requires advanced surgical judgment and skills and the use of highly developed instruments and equipment. Fast technical advances in the development of instruments and surgical techniques require regularly and frequent trainings of surgical skills of all operating personnel as well as modernization and proper maintenance of all surgical equipment and instrumentation.⁸⁴ Wet laboratories using animal models play an important role in modern ophthalmology surgical residency training. In recent times, new virtual reality simulators can be used as a gated, quantifiable performance goal to expert-level benchmarks (Fig. 111.10).^98,99

Fig. 111.10 An EYESI simulator, for training of intraocular surgery in a virtual reality system. The simulator is equipped with a binocular microscope and an eye phantom model to train or improve skills as visual coordination and digital micromanipulations.

Anesthesia

Surgery in proliferative diabetic retinopathy can be performed in local or general anesthesia, sedoanalgesia or a combination of those. The adequate form of anesthesia depends on many factors, as the extent and duration of surgery, the patient’s mental or physical condition, or just the patient’s and surgeon’s choice. It also depends on geographic and economic factors, as there are diverging anesthesia standards in different countries. The patient’s vital signs should be continuously monitored by experienced operating staff members, even during local anesthesia. The advantage of local anesthesia is a minimal disturbance of the diabetic metabolism; however, the patient may feel some pain or move during surgery. Local anesthesia can also be applied during sedoanalgesia or general anesthesia to minimize the patient’s postoperative discomfort.¹⁰⁰ General anesthesia or sedoanalgesia should only be performed by an anaesthesiologist, who can stabilize the patient or help to medically reduce the intraocular pressure. Nitrous-containing agents should not be used or be terminated before an intraocular gas-bubble is injected.^84,100

Preoperative preparation

To provide adequate intraocular visualization, wide pupillary dilatation is always necessary. A combination of different mydriatic, sympathomimetic and cycloplegic drops should be instilled repeatedly before surgery to allow for a maximal pupillary dilatation.⁸⁴ Additional topical medications, as antibiotic or antiphlogistic drops may be added, as well as systemic sedative or diuretic medications for optimal preparation of the patient. If general anesthesia is scheduled, additional preoperative medication or modification of the patient’s medications should be discussed with the anesthesiologist.

In the operating room, a 5% polyvidone iodine solution must be applied on the eyelids and a 5% solution in the conjunctival sack, respectively, and should dry out for at least 3 minutes to guarantee adequate disinfection.¹⁰¹ The eye is then covered with a sterile plastic sheet, equipped with 1–2 side bags, and a lid speculum is inserted (Fig. 111.11).

Fig. 111.11 Preoperative situs before vitrectomy. The eye was covered with a blue plastic sheet, equipped with two side bags, and a lid speculum was inserted. Sterile hand grips were attached on the binocular microscope, and all necessary instruments, as well as a modern phaco-vitrectomy unit, prepared.

Surgical equipment

Microinstruments and illumination

Various types of surgical instruments have been developed and modified over the years. The instruments vary in the number of functions provided. Currently, a trend is towards single-use instruments or parts of them, providing maximal aseptic conditions. For vitrectomy in proliferative diabetic retinopathy, 20-gauge systems have become the long-time standard and are still recommended. They still offer the greatest number of supplementary instruments with minimal flex.^84,108

Small-gauge systems

In the past years, 23-, 25-, and 27-gauge instruments have been developed to provide non-suturing vitrectomy, thereby minimizing inflammation and postoperative discomfort to the patient (Fig. 111.12).^109–112 However, their efficiency in complex cases, such as advanced diabetic retinopathy, is still a matter of debate, as a higher rate of postoperative hypotony has been reported.¹¹³ In the recent literature, 23-gauge systems showed more stable and reproducible results even in severe proliferative diabetic retinopathy, compared with 25-gauge.^109,114,115

Fig. 111.12 Comparison of 20-, 23-, and 25-gauge vitrectomy cutter hand pieces. Notably, the ports of the hand pieces are close to the probe tip.

Basic equipment

The standard equipment for vitrectomy consists of a vitrectomy cutter, combined with a suction unit, a fiberoptic light pipe, an infusion of balanced salt solution (BSS) and an air pump. A modern vitrectomy unit provides all those base functions, in different combinations with diathermy, endolaser coagulation, gas filling or phacoemulsification modules (Fig. 111.13).

Fig. 111.13 Front view of a new Alcon Constellation© vitrectomy unit, providing phacoemulsification, vitrectomy, photocoagulation, diathermy, and air/gas/silicone tamponades in one machine.

Vitrectomy cutter

The vitrectomy probe serves to cut and dissect membranes or fibrovascular proliferations. Shaving of peripheral vitreous or membranous fibrovascular proliferations became significantly safer with the newer probes, where the port is closer to the probe tip.

Illumination

Hand-held illuminators range from single-function illumination probes to multi-purpose illuminated scissors, forceps or vitrectomy probes. The use of “chandelier” light illuminators inserted manually or through additional sclerotomies allows for bimanual dissection.^116–118

Membrane dissecting instruments

A wide variety of tissue scissors, forceps, spatulas, picks or cannulas are available to peel or remove epiretinal membranes; similarly, the vitrectomy probe can be used with lower suction rates at the decision of the surgeon. Vertical scissors may be used for segmentation of tissues in complex fibrovascular proliferations, whereas horizontal scissors are beneficial to delaminate the vitreous cortex from the retina.^119,120

Retinopexy instrumentation

Different endolaser probes for all incision sizes are available to perform panretinal photocoagulation or retinopexy. Scleral depression with an indentator may be used for peripheral treatment. Endodiathermy is useful for stopping bleeding during surgery or for preparing retinotomy sites.

Cataract surgery

Patients undergoing vitrectomy surgery for proliferative diabetic retinopathy may have concomitant cataract. Surgical management options include cataract surgery followed by vitrectomy surgery later, or combined operations in a single procedure.¹⁴⁸ Further variations include cataract extraction, followed by vitrectomy and lens implantation at the end of surgery, or alternatively, cataract extraction with primary lens implantation, followed by vitrectomy. Cataract and vitrectomy surgery may be both performed by one surgeon or two different surgeons, depending on geographic and cultural differences.¹⁴⁸

As cataract surgery has become safer over the years and small incision phacoemulsification is now available, combined phacoemulsification with simultaneous implantation of a posterior chamber lens is performed by our group in patients over 60 years and with signs of cataract. Performing a capsulorhexis without red reflex in an eye with vitreous hemorrhage can be challenging. Here, the vitreous surgeon also has to be an experienced cataract surgeon or this part of the surgery is provided by an anterior segment surgeon. In any case, the dying of the anterior capsule is recommended. In 20-gauge vitrectomy, the infusion line is preplaced but not connected before the lens surgery to avoid pressure created during infusion placement and sutures. In small incision vitrectomy, all three sclerotomies are performed and trocars inserted before cataract surgery for the same reason.

The advantage of any cataract extraction procedure is a much better intraoperative access to the vitreous base, which is of upmost importance in cases of fibrovascular proliferations in diabetic retinopathy or proliferative vitreoretinopathy; there is also evidence that reoperation rates seem to decrease when the lens has been removed during vitrectomy.²⁴

Progression of coexisting diabetic macular edema may be lower when grid/focal laser are applied before cataract surgery, or when panretinal photocoagulation is applied after lens extraction instead of before.²⁰ All cases with proliferative diabetic retinopathy should be treated with panretinal photocoagulation, if possible, and/or anti-VEGF injections before cataract surgery, to avoid a higher incidence of postoperative iris neovascularizations; panretinal photocoagulation may also be applied at time of surgery or shortly thereafter.^21,24 In younger patients with less cataract formation, the loss of accommodation after cataract extraction has to be weighed against possible serious intra- and postoperative complications when the lens was not removed. The patient should be informed that an earlier cataract formation is common after vitrectomy.^17,24 Likewise, it has been reported that in eyes without a crystalline lens, a more complete panretinal photocoagulation and resection of proliferations was possible.²⁴

Glaucoma surgery

Pars plana vitrectomy

Preparation of entry sites

Three-port vitrectomy remains the most used technique, where two sclerotomies are prepared superotemporally and superonasally, and an inferotemporal pars plana incision permits intraocular infusion. Incisions are chosen in 3.5–4.0 mm distances from the limbus. Transconjunctival trocar-guided systems are used with increasing frequency in diabetes-related indications in smaller gauges (23- and 25-gauge) to provide higher comfort for the patients and reduce surgical trauma.¹⁰⁹

To avoid intra- or postoperative wound dehiscence, sclerotomy blades should be oriented parallel to the limbus and trocars should be inserted 20–30° oblique to the scleral surface (Fig. 111.14).

Fig. 111.14 The blade or trocar is directed toward the center of the vitreous cavity to avoid contact with the lens or retina.

However, this technology might be more indicated in easier diabetic cases such as nonclearing vitreous hemorrhage or macular edema.^108,115 In eyes with complex pathologies where silicone oil injection is likely, 20-gauge incisions might provide the surgeon with a higher range of instrumentation and an easier silicone oil tamponade.^108,113,115 Suturing of sclerotomies is recommended in silicone oil use because silicone oil can evade through unsutured wounds subconjunctivally. Precise infusion cannula placement is critical to avoid suprachoroidal infusion and choroidal detachment (Fig. 111.15).

Fig. 111.15 The infusion cannula is inserted and secured with a suture in the inferotemporal pars plana sclerotomy. Indentation of the infusion cannula allows visualization of the unobstructed tip in the vitreous cavity behind the pupil.

A 6-mm cannula can be used instead of the routinely used 4-mm infusion cannula in eyes with anterior displacement of the retina or fibrotic tissue strongly connected with the retina. Sometimes, both hands are needed for dissection of epiretinal tissue with forceps and scissors. Then, a 4-port vitrectomy is needed in which a (chandelier-) light probe is fixed either in the nasal inferior quadrant or at 12 o’clock between the two superior sclerotomies.

Vitrectomy

Light probe and vitrector are inserted through the sclerotomies and vitreous removal is started behind the lens (Fig. 111.16). The infusion is turned on only when the cutter is in the eye and vitreous removal can be started simultaneously. Otherwise, the infusion pressure will move the lens implant anteriorly and iris incarceration into the wound can occur. The anterior part of the vitreous is removed under microscopic view, then a wide-angle viewing system (e.g., BIOM) is inserted and central vitreous removal performed.

Fig. 111.16 The vitreous cutter and fiberoptic illuminator are positioned in the anterior vitreous cavity and visualized through the pupil.

To facilitate identification of the vitreous cortex, triamcinolone acetonide may mark otherwise invisible remnants or patches of vitreous on the retina.^122,123 Due to its anti-inflammatory potential it may also help to prevent fibrin exudation in proliferative diabetic retinopathy. Intravitreal doses of 2–4 mg of triamcinolone acetonide will offer sufficient staining with no retinal toxicity.^102,124

Eyes with complete posterior hyaloid separation

If a nearly complete separation of the posterior hyaloid is present after anterior and central vitreous removal, the posterior hyaloid membrane is incised and the opening enlarged circumferentially to allow adequate visualization of the retinal area (Fig. 111.17).¹² While cutting rate is usually highest (2000–4000 cuts/min), aspiration might be increased in the mid-portion of the vitreous, but should be decreased again during posterior hyaloid removal to avoid unnecessary traction. Blood might be pooled at the posterior pole, usually unclotted, and can be aspirated now with a soft-tipped fluid needle (Fig. 111.18). As precise visualization of the retina is now achieved, areas of neovascularizations or small bleeding sources can be identified. Diathermy should be used for bleeding sources and then the vitreous is removed up to the periphery. Indentation is used to remove all anteriorly located blood and vitreous. Otherwise this can be a source for re-bleeding, tissue contraction and rubeosis iridis. Full-scatter endophotocoagulation is now performed up to the peripheral retina for the same reason.

Fig. 111.17 The vitreous cutter easily incises the posterior hyaloid face, since a complete posterior vitreous detachment is present.

Fig. 111.18 Removal of layered hemorrhage using a soft-tipped cannula.

If a glistening reflex over the fovea is visible, dyes can be used to look for residual preretinal membranes; as well, the internal limiting membrane can be removed. However, if removal of the internal limiting membrane does improve the final visual outcome is still not proven.

In contrast, it was reported from a pilot study that peeling of the internal limiting membrane in proliferative diabetic retinopathy with fibrovascular proliferations might reduce postoperative epiretinal membrane formation.⁴⁸

Finally, an air tamponade can be used to avoid both hypotony and hemorrhage in small incision vitrectomy. In phakic eyes, anterior vitrectomy can be performed using indentation, but usually more residual vitreous will remain than in pseudophakic eyes.

Eyes with incomplete posterior hyaloid separation

If incomplete separation of the posterior hyaloid is present, surgery can be difficult and should remain in experienced hands. Usually a core vitrectomy is performed at the beginning to gain sufficient view over the areas of adhesion and the connections between them. If there is a wide separation between the formed vitreous and the retina, circumferential release of anterior–posterior traction can be achieved with the vitreous cutter. However, if the posterior vitreous is closely overlying the retina in certain areas, care must be taken not to injure the retina (Fig. 111.19). If the retina is attached, gentle suction with the vitrector might be sufficient to further separate the vitreous from the retina to provide safe dissection. If the retina is detached or holes do exist, separation of tissue might be achieved with the use of some viscoelastic to provide higher safety.^157–159 In any case, careful separation, usually with scissors, has to be done. Several surgical techniques for membrane removal have been developed. The first were delamination and segmentation.¹⁶⁰ In segmentation, tractions between centres of adhesions are removed (Figs 111.20, 111.21),^12,52,161 while in delamination, the connections between the posterior hyaloid and/or fibrovascular tissue and the internal limiting membrane are cut (Fig. 111.22).^161–163 The later developed “en bloc” technique includes removal of the vitreous and associated vitreoretinal membranes as a single unit (Fig. 111.23).¹⁶⁴ If only one or few focal adhesions do exist, vitrectomy might be started with a core vitrectomy, followed by excision of the posterior hyaloid over 360° in order to separate small islands of adhesions. If extensive, firm adhesions are present, the “en bloc” technique might facilitate surgery: a core vitrectomy is performed and the posterior hyaloid opened in an area close to or over the optic nerve. The fibrovascular tissue is now grasped with an end-gripping forceps and the tissue separated. Gentle traction is exercised to avoid bleeding or hole formation. If it is possible to loosen the connected tissue over the posterior pole in one piece, then the remaining hyaloid of the peripheral vitreous will lift the residual vitreous and membranes into the mid-vitreous cavity, where it can be removed safely (Fig. 111.24). As tempting as it might sound to remove everything in one big piece, two things need to be mentioned: first, complete removal of membranes and vitreous together in cases with adhesions of different strength is rarely possible. Second, bleeding from several sources might create a less controllable situation. If confronted with a firm adhesion during the “en bloc” technique, a change to delamination or segmentation is advisable. The newer cutters of the 23-gauge systems have an opening nearer to the end tip and do allow segmentation of tissue without additional scissors or picks (Fig. 111.25). The use of some perfluorocarbon to prevent bleeding into the foveal area can be helpful if a bridging membrane has been removed, but further dissection needs to be done in the mid-peripheral retina. If the retina is cleaned from all fibrovascular tissue up to the periphery and bleeding sources are cauterized, circular photocoagulation treatment is performed up to the ora serrata under indentation.

Fig. 111.19 Incomplete posterior vitreous detachment with multiple focal vitreoretinal adhesions. An opening is made in the outer cortical vitreous into the subhyaloidal space in an area of vitreoretinal separation. The cutting port is against the cortical vitreous and away from the retina.

Fig. 111.20 Tangential traction is released with the vitreous cutter by excising the remaining posterior hyaloid and fibrovascular tissue between areas of vitreoretinal adhesions.

Fig. 111.21 When posterior vitreous separation is inadequate to accommodate the vitreous cutter, a plane between the posterior hyaloid and retina can be created with vertical membrane peeler–cutter scissors.

Fig. 111.22 In delamination, fibrovascular adhesions to the posterior hyaloid are excised parallel to the retinal surface with horizontal scissors.

Fig. 111.23 En bloc vitrectomy. After an opening is made in the posterior hyaloid adjacent to vascular epicenters, membrane peeler–cutter scissors enter the subhyaloidal space. The unremoved formed vitreous provides anterior traction that helps separate the vitreous and fibrovascular tissue from the retina and helps identify sites of adhesion.

Fig. 111.24 After all posterior adhesions have been released, the vitreous cutter is used to excise the detached formed vitreous and associated fibrovascular membranes en bloc.

Fig. 111.25 Fibrovascular tissue that is firmly attached to the disc is reduced with the vitreous cutter.

Eyes with subtotal posterior vitreous adhesion

If the posterior hyaloid is almost completely attached to the retina, access to the subhyaloidal space is difficult. After a core vitrectomy is performed, gentle suction can be used to find areas where the vitreous is lesser adherent. Usually, these are areas of subhyaloidal hemorrhage. As it is not possible to incise this tissue with the vitrector, a sharp blade or subretinal pick is used to create an opening into the subhyaloidal space. The safest areas for such manoeuvres are around the optic disc. Once part of the hyaloid is lifted, a patient separation of the fibrovascular tissue is needed.

Usually, dissection is performed centripetally. Again, bleeding sources need to be cauterized immediately, and it is mandatory to maintain a controlled situation. If retinal holes are detected under proliferating tissue or created during preparation, the surrounding tissue must be excised without residual traction. Also here, some perfluorocarbon might be helpful to flatten out a localized retinal detachment and facilitate sufficient laser treatment of the holes. As already mentioned above, careful panretinal laser treatment is performed once the retina is cleaned. The tamponade of choice can be either a longer acting gas tamponade or silicone oil.

When identifying the posterior vitreous cortex in diabetic patients, surgeons should be aware of posterior vitreoschisis, simulating posterior vitreous separation (Fig. 111.26).^91,165 If this phenomenon is unrecognized, only the inner wall of the vitreoschisis will be removed, leaving much traction unrelieved.¹²

Fig. 111.26 Posterior vitreoschisis. Split hyaloid with partial vitreous separation. Although there is unseparated posterior hyaloid (white arrow), there is a pseudohyaloidal membrane (black arrow), giving the illusion of vitreous separation. The pseudohyaloidal membrane may be the result of condensed vitreous collagen that is often found after a hemorrhage in formed vitreous.

Eyes with combined tractional and rhegmatogenous detachment

In eyes in which rhegmatogenous retinal detachment is present in addition to tractional detachment, great care not to aspirate and cut inadvertently into the retina has to be taken during the whole surgery. Core vitrectomy is done with lesser suction than usual and the tissue is carefully inspected before cutting. Once a clear overview of the retinal situation is created, dissection of tissue is started usually in an area distant from the detached retina. Still, preparation of tissue from the centre to the periphery is advisable. Perfluorocarbon can be used to stabilize the posterior retina, while further tissue removal in the periphery is performed. However, if an atrophic retinal detachment is present, the use of perfluorocarbon can be dangerous because the retina is inelastic and shortened. A primarily small retinal hole can turn into a large retinal hole and perfluorocarbon may glide in the subretinal space. A similar situation can occur when silicone oil tamponade is used too early and the retina is still under traction. Careful inspection of the periphery under indentation is needed, and anteriorly dislocated retina is either freed from fibrotic tissue or cut. Retinectomies and retinotomies should be used only in selected cases and performed as last resort (see also Chapter 108, Retinectomy). They cannot replace careful membrane dissection. Usually peripheral retinectomies are needed in eyes where reoperations become necessary and severe anterior hyaloid fibrovascular proliferation has developed. Before the retina is cut, diathermy is applied to the anterior and posterior margin of the retina and the vessels to be excised. The extension of the retinotomy should reach normal retinal area around the area of traction. The retina can be cut either with the cutter or scissors. If not already detached, a shallow detachment must be created in order to cut without traumatizing the choroid or creating hemorrhage. It is mandatory in diabetic vitrectomy to release all tractions around retinal holes before tamponades can be used. The anterior part of the retina is also trimmed and cauterized in retinectomies to avoid secondary fibrosis of residual anterior retina and traction on surrounding tissue and/or the ciliary body. Smaller posterior retinotomies can also become necessary, if persistent traction around an old tear exists. Silicone oil is the tamponade of choice for diabetic eyes requiring retinectomies. Eyes requiring retinectomies have a poorer outcome and visual prognosis than those not requiring.¹⁶⁶ Placement of a scleral buckle can be added to complex surgery in diabetic vitrectomy. It is usually performed in reoperations or as a primary surgery in younger diabetic patients where massive activity and fibrovascular proliferation and detachment exist, but visual acuity is still useful.

In primary procedures, the retina is usually more elastic and an additional encircling band might make a large retinectomy unnecessary. Usually, the surgery is started with episcleral surgery. The conjunctiva is dissected over 360° at 1–2 mm distance from the limbus and Tenon’s capsule peritomy performed. Four sutures are placed under each rectus muscle and four 5.0 nylon mattress sutures prepared in each quadrant to secure the band. The anterior suture is placed 2–4 mm behind the insertion of the rectus muscles, the posterior suture depends on the size of the band. For a 4-mm band at least a 6-mm distance between sutures has to be chosen in order to create indentation. When the silicone band is placed under the muscles and the sutures, sutures are fixed and the ends of the band secured.

The buckle should be relatively shallow and mainly support the vitreous base. A paracentesis can be performed to reduce pressure during buckle placement. Certainly fixation of the cerclage can be postponed until after vitrectomy, but this makes a change from internal surgery to external surgery necessary. In eyes where lens surgery is planned, an inferior sclerotomy is placed to allow some liquefied vitreous to escape. Then the infusion line is prepared but not turned on. If the eye pressure is too high, a second or third paracentesis is performed. If the anterior chamber is deep enough to allow cataract surgery, a small limbal incision is performed and the anterior chamber filled with viscoelastic. Routine phacoemulsification and intraocular lens implantation follows as next surgical step. A permanent or transient 10.0 nylon suture to seal the cataract wound is advisable in complex diabetic vitrectomy, where changes in intraocular pressure can be expected during and after surgery.

Examinations

Regular ophthalmic examinations are scheduled according to the individual case; however they should be performed on a daily basis in the first postoperative days. Additional examinations are necessary when the patient complains of abnormal or increasing pain, especially in cases with a history of glaucoma or when expanding gas bubbles were used. It is reasonable to perform further examinations on a weekly basis in the first month and on a monthly basis until the eye has stabilized and/or local or systemic medications are stopped.⁸⁴ Finally, periodical routine examinations every 3–6 months are recommended, according to the severity of diabetic retinopathy. In the routine examinations, the anterior segment must be checked for unexpected inflammation, media opacities or signs for neovascular glaucoma, as rubeosis iridis. Intraocular pressure is monitored and normalized to prevent pain or eventual visual field loss. The posterior segment must always be carefully examined to observe the healing process and identify possible complications. Macular edema or tractional detachment may take time to resolve and can be monitored by optical coherence tomography. Written instructions, as medical prescriptions or visits, are always preferred.^41,84,171

Hospitalization and convalescence

The length of hospitalization is determined by the extent of surgery and the condition of the patient. Cataract surgery is usually performed on an outpatient basis, whereas after vitrectomy or complicated surgery, hospitalization is required. The management of patients with pain or elevated intraocular pressure, who need more frequent examinations and adaptations of their medication, is always more efficient in hospital.⁸⁴ Furthermore, good diabetic and general medical control is necessary (see below).

When surgery on outpatient basis is performed, it is important to carefully instruct the patient for further behavior, medications and visits. For confused or disoriented patients, it is important that responsible persons always accompany the patient. Postoperative positioning is of great importance when intraocular gases were used, depending on the location of retinal breaks, and may be facilitated with pillows and tables.⁴¹ Normally, adhesion of the retina to the retinal pigment epithelium occurs in 1–4 days after retinopexy.^172,173 Face-up positioning might accelerate cataract formation in phakic eyes, iris capture in pseudophakia or loss of anterior chamber in aphakia.^174,175 If additional laser treatment is needed when a gas bubble is in the eye, the surgeon should be aware of unintentional retinal damage from laser beam reflection at the fluid/gas interface.¹⁷⁶ In cases with intraocular silicone oil tamponade, positioning is less critical. However, silicone oil changes the refractive power of the eye and interferes with diagnostic ultrasound, possibly hampering follow-up examinations or axial length measurements.^177,178 Despite the need for early silicone oil removal due to complications, silicone oil is usually removed after 3–6 months at the decision of the surgeon. Recurrent retinal detachment is rare after silicone oil removal and appears to be independent of the duration of silicone oil tamponade.^179,180 In most severe cases, silicone oil might be also used as long-term tamponade to prevent phthisis of the eye.^141,181

Medications

The common preference for few topical medications in ophthalmology might differ after surgery for proliferative diabetic retinopathy, especially in more complex cases. Patients will rarely feel heavy pain after vitrectomy, but it can happen more frequently after additional buckling surgery.⁸⁴ Oral analgesics are usually sufficient, but sometimes additional intravenous analgesics are needed. The use of patches did not appear to be helpful in controlling pain from corneal abrasions; however, pain from corneal epithelial defects might be mild due to diabetic neuropathy.^182,183 An increase of intraocular pressure needs topical or systemic pressure lowering medications. Topical cycloplegic drops provide pupillary dilatation, immobilization of the ciliary body, reduction of inflammation and the risk of synechia formation.⁸⁴ In addition, topical antibiotics, steroids, and anti-inflammatory drops are prescribed in the first postoperative days or weeks to minimize inflammation and prevent infection. Steroids may be administered periorbitally during or after surgery. In severe cases, systemic anti-inflammatory drugs or corticosteroids might be added, but can interfere with the patient’s antidiabetic medication. A sudden, increasing inflammation raises suspicion of endophthalmitis and needs urgent intravitreal antibiotic injection, vitreous culture and vitrectomy.

Further surgery

After cataract surgery, proliferative diabetic retinopathy must be sufficiently treated or re-treated with panretinal photocoagulation if not already performed at time of cataract surgery.²¹ Similarly, diabetic macular edema progression may be slightly lower when grid/focal laser are applied after lens extraction instead of before.²⁰ In patients who had vitrectomy surgery with silicone oil instillation, recurrent retinal detachment after silicone oil removal is unusual and seems not to be related to the duration of silicone oil tamponade.^179,180 In most severe cases, silicone oil might be used as a long-term tamponade to prevent phthisis.^141,181 In earlier times, an increased risk for the development or increase of rubeosis iridis was postulated after vitrectomy with cataract extraction or lensectomy; however, recent series do not support this theory anymore, although in the absence of preoperative panretinal photocoagulation, adjunctive treatments with panretinal photocoagulation, anti-VEGF injections or glaucoma filtering surgery might be useful.^24,149,184

Diabetes control

The challenge for the primary care physician and the diabetologist in all patients with diabetic retinopathy is to attain excellent glycemic control, aggressive control of blood pressure and normalization of lipids.¹⁸⁵ After surgery for proliferative diabetic retinopathy, diabetic patients are at increased risk for adverse outcomes, which are related to pre-existing complications of diabetes, especially atherosclerotic disease, nephropathy and peripheral and autonomic neuropathy; similarly, hyperglycemia is associated with a higher risk for poorer wound healing or infections,¹⁸⁶ and a possible loss of nutrients through glycosuria.¹⁸⁷ The use of insulin offers great flexibility of timing and dose in the postoperative management of most diabetic patients. Short-acting insulin analogues have been shown to work well as pre-meal medication or as rapid counteraction against pronounced hyperglycemia for outpatients as well as hospitalized patients.¹⁸⁷

On the other hand, rapid-acting insulin analogues may be associated with an increased risk for hypoglycemia, if the delay to the next meal is too long.¹⁸⁸ Accordingly, oral sulfonylurea and other insulin secretagogues lower blood glucose levels acutely; however, the risk for hypoglycemia is smaller with non-sulfonylurea agents.¹⁸⁷ In general, hospitalization provides a chance to organize long-term diabetes management issues: advice and information of optimum nutrition, exact glycemic control, management of hypertension or dyslipidemia as well as basic guidelines for foot care should be given during this time. Finally, an appropriate diabetes education for newly diagnosed or poorly controlled diabetic patients, arrangements for medical nutrition, and regular medical follow-up visits are important to attain the best possible long-term surgical and medical outcomes.^187,188

Intraoperative complications

New technologies and improved understanding of the disease process have reduced both numbers and severity of complications in diabetic vitrectomy. Nevertheless, complications do occur and proper management is essential to achieve a successful completion of the surgery.

Postoperative complications

The most frequent postoperative complications after vitrectomy for diabetic retinopathy are elevated intraocular pressure, corneal erosion, fibrin formation, bleeding, and retinal detachment.

Anterior hyaloidal fibrovascular proliferation

AHFVP is a most severe complication following diabetic vitrectomy, occurring in up to 13% of cases (Figs 111.27, 111.28).^41,219 The presentation of AHFVP includes the growth of neovascular tissue onto the vitreous base, the anterior retina, ciliary body, lens capsule and iris. Therefore patients may present with rubeosis iridis, vitreous hemorrhage, peripheral tractional retinal detachment or hypotony.⁴¹ Risk factors for AHFVP include male gender, type I diabetes, phakic patients, insufficient panretinal photocoagulation, severe ischemia with recurrent neovascularizations, and previous surgery with placement of a scleral buckle.²¹⁹ The origin of the disease may be at the sclerotomy sites, or at the peripheral retina.^41,97 For treatment, cataract extraction, lensectomy, scleral buckling, extensive laser or cryopexy, and anterior dissection with eventual retinectomy might become necessary.²¹⁹ As membranes are highly vascularized, preoperative injections of bevacizumab can be helpful for short-term regression during vitrectomy.²²⁰ The functional prognosis is always poor; therefore, all efforts for prevention and early detection of AHFVP should be taken.⁴¹

Fig. 111.27 Anterior hyaloid fibrovascular proliferation. Peripheral retinal fibrovascular proliferation is seen extending on the posterior lens capsule.

Fig. 111.28 Microscopic features of anterior hyaloid fibrovascular proliferation. The peripheral retina is detached and displaced anteriorly by fibrovascular tissue originating in the retina and extending along the anterior hyaloid towards the posterior lens capsule (H&E; ×30).

Cataract

There is a frequent coexistence of cataract and proliferative diabetic retinopathy.^221,222 Improvement in acuity after cataract surgery may be achieved in >55% of patients,²²³ but long-term results are generally inferior to patients without diabetes. The Early Treatment for Diabetic Retinopathy Study (ETDRS) reported a gain of ≥2 lines in 64.5% of eyes with early, and 59.3% of eyes with delayed panretinal photocoagulation one year after cataract surgery.^185,224 However, the literature regarding optimal timing of cataract surgery and panretinal photocoagulation, with respect to maximal visual gain and minimal risk of diabetic macular edema, is scarce.⁷⁰ There were reports about progression of untreated proliferative diabetic retinopathy after extracapsular cataract surgery or development of vitreous hemorrhage in 20% of patients after intracapsular surgery.^19,20,225 Another randomized study reported that panretinal photocoagulation treatment shortly after cataract surgery was associated with less macular edema and less acuity loss than with panretinal photocoagulation right before cataract surgery.⁷⁰ As levels of intraocular VEGF and other cytokines are elevated after cataract surgery, intraocular injections of triamcinolone acetonide or anti-VEGF agents are indicated to stabilize the eye if panretinal photocoagulation cannot be adequately applied before cataract surgery.^226–230

Similarly, those agents may be helpful in cases of diabetic macular edema with the risk of deterioration after cataract extraction.²³¹ Cataract surgery before or during vitrectomy was reported to produce faster visual recovery and less vitrectomy reoperations.^232–236 Disadvantages are a poor red reflex in eyes with vitreous hemorrhage and a higher rate of postoperative inflammation or synechia formation.^237–240 Inflammation has shown to be lower in two separate procedures or in combined vitrectomy with pars plana lensectomy procedures, especially in complicated tractional detachment cases requiring silicone oil tamponade.^{22,238,241–245}

In all cases with combined surgery, independent of timing, additional complications may occur: capsular tears, zonulolysis (10%), anterior capsule opacification and traction, hypotony, or ciliary body effusion.^{238,246–248} The risk of rubeosis iridis and neovascular glaucoma, on the other hand, is diminished to <1% with appropriate application of panretinal photocoagulation.^6,236,249 Visual outcome is related to the severity of diabetic retinopathy, according to the ETDRS.²⁴⁹ Therefore, patients with proliferative diabetic retinopathy are far less likely to achieve a 20/40 or better acuity than patients with non-proliferative diabetic retinopathy.^223,249 In summary, the general effect of cataract surgery on the progression of diabetic retinopathy, diabetic macular edema or proliferative diabetic retinopathy is still a matter of debate. Although literature is insufficient, it seems that if diabetic macular edema or proliferative diabetic retinopathy is sufficiently treated with laser and/or anti-VEGF medications before cataract surgery, no significant progression of diabetic retinopathy should occur.^249–251

Vitreous hemorrhage

In diabetics with non-clearing vitreous hemorrhage, the benefit of early vitrectomy, defined as 1–4 months from onset, was clearly demonstrated by the DRVS.²⁷ Patients with visual acuity <5/200 and vitreous hemorrhage for 1–6 months were enrolled and randomized into an early and late surgery group, where vitrectomy was delayed for 12 months. Recovery of vision was significantly better for early surgery, compared to late surgery, at 3 months (50% versus 17%); 2 years (25% versus 15%) and 4 years, accordingly. Benefits were much better for patients with type 1 (36% versus 12%) than for those with type 2 diabetes mellitus (16% versus 18%), probably because of the more severe course of proliferative diabetic retinopathy in type 1 diabetic patients.²⁷ Also, the poorer results for type 2 diabetics could be a consequence of a higher rate of maculopathy or posterior vitreous detachment in those cases. In addition, it should be noted that the DRVS preceded the use of the most contemporary equipment, including intraocular and indirect laser systems. Other retrospective studies for diabetic vitreous hemorrhage reported an improvement of acuity in >80% of operated cases, with a final vision of 20/200 or better in 48–72% of eyes, with a proportion of 20/40 or better in up to 38%.^30,217 Good prognostic factors are a preoperative vision >5/200, no neovascular glaucoma or rubeosis, no or minimal cataract, and pre-existing panretinal photocoagulation in at least one quadrant.^30,217 Cases of associated anterior segment neovascularization (rubeosis iridis or manifest neovascular glaucoma) and/or severe progressive proliferation of the fellow eye are indications for an early vitrectomy.^25,27 Postoperative vitreous hemorrhage after vitrectomy is common; however, only 4–10% of cases will require another vitrectomy, according to the literature.^{25,30,163,217,218}

Diabetic maculopathy and macular traction

The benefits of early vitrectomy in cases with advanced proliferative diabetic retinopathy and macular traction, despite hemorrhage or retinal detachment are known since the DRVS^7,252: in eyes after early vitrectomy, a final acuity of 10/20 or better after 4 years could be reached in 44% compared with 28% of the non-operated eyes (P < 005).^7,70,252 Other authors reported improved vision after vitrectomy for macular traction detachments in 59–80% of cases, with a postoperative acuity of ≥20/200 in 21–58% of cases.^63,253–255 Starting in the 1990s, several authors have also reported good anatomical and functional effects of vitrectomy in persistent diabetic macular edema;^256–261 the procedure of surgically induced vitreomacular separation based on the finding that a posterior vitreous detachment was less frequent in patients with diffuse diabetic macular edema than in diabetic controls without edema.^262–265 Similarly, one trial reported about a resorption of diabetic macular edema in 55% of patients with posterior vitreous detachment, in contrast to only 25% of patients without.²⁶⁵ Consequently, a large number of mostly retrospective cases series and trials have been conducted, performing vitrectomy for diabetic macular edema in eyes with taut hyaloid adherent to the macula,^{257–259,266,267} in eyes with attached, but non-thickened hyaloid,^268–271 in eyes with persistent diabetic macular edema despite previous laser or anti-VEGF therapy,^272–274 or as primary therapy in eyes with severe diabetic macular edema irrespective of posterior vitreous detachment.^275–279 One trial in eyes with diabetic macular edema unresponsive to laser therapy and a taut, adherent hyaloid reported a functional improvement of two lines in 49%, and a reduction in diabetic macular edema in 94.5% of patients.^70,259

However, the majority of those trials lack homogenous inclusion criteria or even an accurate definition of such criteria (as “taut hyaloid” or “macular thickening”).²⁷⁹ Similarly, the effect of internal limiting membrane peeling is still controversially discussed; potential benefits in releasing traction have to be weighed against surgical complications, as possible toxic effects of indocyanine green staining.^280–282 Other open questions include different intraoperative steps that could affect diabetic macular edema: enzymatic adjuncts, panretinal photocoagulation or focal laser treatment, cataract extraction or concomitant injection of anti-VEGF medications.^{277,278,280,283} Interestingly, the effect of vitrectomy was found to be independent of pre-existing posterior vitreous detachment in one case series, indicating other causative factors for diabetic macular edema, as different cytokines.^278,284 Finally, results show a large variety concerning the effects of vitrectomy. Even in those trials reporting both morphologic and functional improvements, the effects on morphology have been always more pronounced than the acuity gain. This could be the consequence of ischemia, more subretinal exudates, longer duration of diabetic macular edema or damage of previous therapies.^285–288 Therefore, at least some agreement exists about which conditions may negatively affect the outcome after vitrectomy for diabetic macular edema: previous focal/grid laser therapy, presence of submacular fluid, longer duration of diabetic macular edema, significant ischemia or subretinal fibrosis.^{287,289–292} In sum, for best ophthalmic treatment, it is not only necessary to know the different techniques, risks and benefits of vitrectomy in diabetic maculopathy; the most important clinical issue is whether to attempt focal/grid laser therapy or intravitreal antiangiogenic injections prior to surgery to treat the nontractional component of diabetic macular edema.^279,293

For the future, large controlled, randomized, multicenter studies will hopefully provide a better definition of the role and efficacy of vitrectomy in diabetic macular edema.

Retinal detachment, tractional detachment and proliferative vitreoretinopathy

Outcomes of vitrectomy for retinal detachment in proliferative diabetic retinopathy are generally worse than for diabetic vitreous hemorrhage alone.^6,294 For diabetic tractional detachment, visual improvements of ≥2 lines have been reported in 60–75% of cases, with a mean postoperative acuity of ≥20/200 in 47–57% of patients, or ≥5/200 in 69–77% (Table 111.1).^{54,55,164,296–299} An overall persistent reattachment rate of 82% was reported within 6 months,^300,293 with successful anatomic reattachment of the macula in 80–100%.^54,56,299 In contrast, for cases with complete tractional detachment, average reattachment rates were approximately 56%.⁵⁵ Results for combined rhegmatogenous and tractional detachments or long detachments including the macula were even worse than for cases with tractional detachment alone. These subgroups reach visual improvements in 20–53%, a final acuity of ≥20/200 in 25–36%, and a final acuity of ≥5/200 in 55–68% of all eyes, on average.^{58,253,294,300} Retinal reattachment was reached in 47–82%. With the use of encircling bands and silicone oil, attachment rates of 73–93% could be reached.⁴¹ Improvement in vision increased to 64–81% with a final acuity of ≥5/200 in 55–68% of eyes.^{41,63,294,301,302} Parallel, the incidence of phthisis decreased from 10% to nearly 0%.

Functional results are often disappointing, although a good anatomic success is achieved; this may be the consequence of (longstanding) retinal or macular ischemia, optic disc atrophy or retinal thinning. Other conditions that negatively influence the outcome, are preoperative rubeosis iridis, neovascular glaucoma, age >50 years, visual acuity <5/200, ischemic maculopathy, vitreopapillary traction, lack of panretinal photocoagulation, vitreous hemorrhage, fibrinoid syndrome, or AHFVP.^{6,52,55,58,70,241} As anatomic and functional results after vitrectomy have substantially improved, so too has the management of peripheral retinal tractional detachment in recent times. Generally, there is a better prognosis, with a risk of only 14% of severe visual loss per year.^52,70,303 Nevertheless, an earlier surgical approach in those cases seems reasonable to avoid the risk of macular involvement with poorer prognosis.^53–55,237 The need for vitrectomy reoperation generally ranges from 24% to 47% after diabetic tractional detachment, and from 29–90% after combined rhegmatogenous and tractional detachment, excluding laser treatment.^{54,56,58,63,181,279,294}

Secondary glaucoma (neovascular glaucoma)

At earlier stages of neovascular glaucoma with rubeosis and normal or moderately elevated intraocular pressure, panretinal photocoagulation alone can normalize pressure in 33–88% of patients.³⁰⁴ Regression of rubeosis can be achieved in 33–94% of patients, depending on how many quadrants of anterior synechia are present.^149,305 In more advanced, refractory neovascular glaucoma, glaucoma filtering surgery is still the most promising approach; however, long-term success rates have been relatively poor, with an effective 5-year-control of intraocular pressure in only 25–30% of operated eyes. Similar results are reported for glaucoma implants, using Ahmed, Molteno, or Baerveldt valves.^149,306,307 A better control of intraocular pressure has recently been shown by panretinal photocoagulation and glaucoma implant surgery 1–2 weeks after an intravitreal injection of bevacizumab.¹⁵⁰ Success rates were 85% for patients who received adjunctive bevacizumab plus panretinal photocoagulation, compared with 70% for those who were given photocoagulation alone.^149,308,309 As an alternative treatment option, vitrectomy with photocoagulation may help to treat or prevent rubeosis iridis.^71,72 In earlier reports, a substantial risk of development or progression of iris neovascularizations after vitrectomy in 8–26% of phakic and 31–55% of aphakic eyes was described;^15,310 however, recent series do not support this hypothesis anymore, quantifying the risk to <5%.^149,295 The risk may be somewhat higher (OR = 1.7) in the absence of preoperative panretinal photocoagulation.⁶¹ In eyes with advanced neovascular glaucoma and low visual function, transscleral cryo- or diode-laser cyclocoagulation have proven as effectively as trabeculectomy or drainage implant surgery.^153,154