Corneal surgery

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CHAPTER 21 Corneal surgery

Chapter outline

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Corneal and anterior segment trauma

Amit Patel, Massimo Busin and Carlo Enrico Traverso

The conjunctiva and cornea as the most anterior structures of the eye are prone to damage from a variety of insults. It is important to gauge the extent of injury, decide whether the trauma requires medical or surgical treatment, and determine the realistic functional prognosis. This assessment must be made in context of the whole patient and life-threatening injuries must be excluded prior to any ocular injury. Although the present text relates to anterior segment and corneal trauma, scleral and posterior pole injuries might coexist and need appropriate diagnosis and treatment.

Preoperative evaluation

Corneal laceration

Not all corneal lacerations require surgical intervention. Small self-sealing or minimally leaking corneal lacerations may be treated with topical antibiotics and cycloplegics. A bandage contact lens or glue may be used in cases where a slow wound leak is present.

Large full-thickness lacerations, or those that continue to leak after 1 or 2 days, are best treated by surgical closure. Surgical intervention should also be considered in large, deep or gaping partial-thickness lacerations in order to minimize corneal scarring and irregularity. In severely traumatized corneas where there is loss of tissue, a donor patch graft or penetrating keratoplasty may be indicated.

Viscoelastic may be injected through the wound or via a paracentesis to reform the anterior chamber if required. 10.0 Nylon is preferably used to close the corneal laceration. The placement of the primary suture depends on the configuration of the wound. When linear, it is placed at the center of the wound with subsequent sutures bisecting the remaining portion. If angulated, the primary suture is placed at the apex of the laceration. Stellate ruptures are difficult to repair and may require triangular, ‘X’ or purse-string sutures (Fig. 21.1). Attempts should be made to place sutures outside the visual axis if possible.

Particular care should be taken when placing sutures in bevelled lacerations. The entry and exit points of the sutures should be appropriately placed in order to avoid overriding of the wound edges or dehiscence secondary to ‘cheese-wiring’ of the tissue (Fig. 21.2).

Any viscoelastic in the anterior chamber must be replaced with balanced salt solution in order to avoid extreme intraocular pressure (IOL) spikes and any anterior synechiae lysed with a cyclodialysis spatula. A Seidel test is performed after closure to ensure a watertight closure.

Hyphema

Most traumatic hyphemas may be treated medically; however, surgical intervention should be considered in cases with prolonged and severely raised IOP, which may lead to optic nerve damage and corneal staining1. The corneal staining may develop rapidly, especially in younger individuals, but can take several months or years to clear.

Surgical evacuation of the blood is indicated in cases where: (i) early corneal staining is noted, especially in the amblyopic age; (ii) the IOP has been over 40 mmHg for 2 days or over 30 mmHg for 7 days; (iii) the patient has sickle cell hemoglobinopathy or trait and raised IOP. Persistent total hyphemas may also be evacuated to prevent peripheral anterior synechiae and chronic intraocular pressure elevation.

Removal of the blood clot may be carried out with a mechanical vitrector or irrigation and aspiration2. Two paracenteses are made and an irrigation cannula or anterior chamber maintainer placed in one and a vitrector in the other. The aspiration and cutting functions of the vitrector are effective in removing the clot whilst minimizing traction on the iris and iridocorneal angle. Irrigation and aspiration may also be used without the cutter; however, the clot may be too thick to be evacuated and may result in unnecessary traction.

Intraoperative bleeding may occur and adequate tamponade should be applied to stop the bleeding. This may be achieved by elevating the intraocular pressure and/or injecting viscoelastic material at the site of bleeding. Injection of an air bubble into the anterior chamber with intraocular pressure elevation may also be effective. Viscoelastic material if used should be carefully removed in order to prevent postoperative intraocular pressure rise.

Lens trauma

Lens injury following anterior segment trauma may be in the form of cataract, luxation, rupture, or extrusion. In the presence of an intact lens capsule, the cataractous or subluxated lens need not be addressed at the time of primary repair. This allows time to evaluate the extent of injury, carry out appropriate biometry, and plan for elective surgery. Capsular rupture, lens induced inflammation, and secondarily elevated IOP generally necessitate lens removal at the time of primary repair.

In cases where the lens requires extraction, opinions vary on the timing of intraocular lens (IOL) implantation. A posterior chamber IOL may be placed at the time of primary repair if the wounds are clean, the posterior capsule intact, and no posterior segment trauma/foreign body is present. In such cases, biometry of the contralateral eye may be used to gauge the required IOL power.

Poor visualization due to the corneal trauma and uncertainty of the capsular and zonular integrity pose a challenge for cataract extraction at the time of primary repair. A separate limbal incision is created following repair of the corneal laceration. The anterior capsular tear may be converted either to a curvilinear capsulorrhexis or to a ‘can-opener’ type of capsulotomy. Gentle hydrodelineation may be carried out and in most cases the lens can be aspirated with minimal phacoemulsification. Care should be taken to avoid undue stress on the zonules and there should be a high index of suspicion for zonular weakness, anterior and posterior capsular tears, and vitreous prolapse.

Conjunctival flap surgery

Amit Patel, Carlo Enrico Traverso and Massimo Busin

Conjunctival flap surgery has been used for many years to manage various corneal and ocular surface diseases. Over time, development of newer drugs, lubricants, bandage soft contact lenses, and collagen shields has diminished the indications and need for conjunctival flaps. However, despite this and the advent of amniotic membrane transplantation, there is still a group of patients for whom conjunctival flap surgery is a viable and effective solution.

Of the numerous techniques to cover the cornea with conjunctiva, the total conjunctival flap popularized by Gundersen4 and the partial conjunctival flap are the most effective. The aim of conjunctival flap surgery in ocular surface disease and ulceration (both infectious and non-infectious) is to prevent stromal melting and possible perforation, thus stabilizing the eye and eventually allowing later surgery aimed at rehabilitating vision. However, for conditions that do not allow later corneal surgery (i.e. extreme dry eyes, high grade stem cell deficiency, etc.) a conjunctival flap may be compatible with vision up to 20/400 (see Fig. 21.4C).

Indications

Conjunctival flaps may be utilized in a variety of corneal diseases that are not responsive to medical management, induced ptosis, or tarsorrhaphy. Chronic ocular surface disease and non-healing corneal epithelial defects are excellent candidates for flap surgery5. It has also been used to stabilize the eye in chronic and non-response viral, bacterial, and fungal corneal infections68. In the presence of a descemetocele or perforation, a corneal patch must be carried out prior to considering a conjunctival flap.

Along with providing corneal support and fibrovascular tissue to fill epithelial defects, the associated blood supply aids to bring immunoglobulins, anticollagenases, and systemic antibiotics to the lesion9. This advantage is not afforded when applying non-living tissue such as amniotic membrane. Other indications include neurotrophic ulcers, marginal ulcers, exposure keratopathy, and bullous keratopathy with low visual potential.

Surgical technique

Total conjunctival flap

Peribulbar or retrobulbar anesthesia may be administered and an eyelid speculum creating good exposure of the conjunctiva is inserted. The corneal epithelium is removed with a sharp rounded blade or alcohol. Any necrotic stroma tissue is also removed carefully. The debridement is best performed at the beginning of surgery so as not to neglect to perform it after the flap is created. In addition, any bleeding at the limbus will have had time to undergo hemostasis while the flap is being fashioned.

A 6.0 silk or polyglactin 910 traction suture may be placed through the cornea near the limbus to allow downward rotation of the globe during flap dissection. The superior conjunctiva is dissected from the underlying Tenon’s tissue by injecting 1–2 ml of local anesthesia (e.g. 1–2% lidocaine) or balanced salt solution with a 27 gauge needle. Epinephrine in a dilution of 1 : 100 000 may be added to achieve temporary vasoconstriction. The injection site should be situated away from the conjunctiva intended for flap use so as to prevent creating a ‘buttonhole’. A small horizontal incision is made with Wescott scissors at the fornix through conjunctiva, but not into Tenon’s fascia. Then the blunt and sharp dissection is performed with Wescott scissors and non-toothed forceps, separating conjunctiva from Tenon’s, ideally in the plane created by the local anesthesia. Dissecting the conjunctiva with the scissors placed underneath (Fig. 21.3A and B), as opposed to under direct visualization, ensures that the correct plane is maintained and minimizes the risk of buttonhole formation. The dissection is carried out in a meticulous fashion to the limbus and care is taken to avoid buttonholes, although this may be difficult in eyes that have had chronic inflammation, scarring, surgery, or trauma.

Once most of the conjunctiva is dissected down to the limbus, the horizontal incision can be extended several millimeters toward the nasal and temporal canthi (Fig. 21.3B). The nasal and temporal portions of the flap then need to be undermined. Once the entire flap has been created, the conjunctival dissection is continued forward until it comes free at the limbus. A 360° conjunctival peritomy is then performed. A small amount of undermining of the inferior limbal conjunctiva often makes the peritomy and subsequent suturing of the conjunctival edge easier. The limbus is then debrided of any remaining epithelium.

The ocular surface is irrigated and the flap carefully slid over the cornea. It is first sutured inferiorly to episclera and the inferior conjunctiva using interrupted 8-0 absorbable sutures (e.g. Vicryl). Once the flap is secured inferiorly, the superior edge is secured to the Tenon’s and episclera without excessive tension. Care is taken to avoid imbedding a fold of conjunctiva. The crescentic area of bare episclera which remains in the area from where the flap was obtained, usually epithelializes within days. An inferior conjunctival flap may be considered to spare the upper quadrants when filtration surgery is likely to be needed in the future.

Buttonholes of the flap are the most common intraoperative complication and can lead to flap retraction. These should be closed with interrupted or purse string sutures and, if located in an area of flap that covers the cornea, the sutures should be anchored to the underlying cornea. Fig. 21.4 illustrates the pre- and postoperative appearance of a total conjunctival flap. Failure to separate Tenon’s fascia from the overlying conjunctiva leads to fibrovascular proliferation and poor transparency (Fig. 21.5).

Partial conjunctival flaps

Localized limbal and paralimbal lesions in an otherwise healthy cornea may occasionally be treated with a partial conjunctival flap. The corneal epithelial debridement is carried out in the area expected to be covered by the conjunctival flap and the conjunctiva is ballooned with local anesthesia as described above. The width of the conjunctival flap should be approximately 1.5 times the width of the lesion to be covered in order to allow for proper suture placement and account for late flap retraction. In order to secure the conjunctival edge onto the cornea and prevent dehiscence and retraction, it is important to create a ledge of cornea into which to suture the conjunctiva. A groove is made into healthy cornea at the edge of the intended extension of the flap with a diamond or metal blade and a small triangular strip of cornea is removed to create a ledge (Fig 21.6).

The partial flaps may be fashioned in various ways. A simple advancement flap is created much in the same manner as a total flap; however, the amount of conjunctival dissection is smaller and the edge of the flap is sutured on to the cornea with 10-0 nylon sutures. An advancement flap is prone to retraction with time and a relaxing incision through the conjunctiva and Tenon’s tissue, away from the limbus, may reduce the likelihood and allow the bulbar conjunctiva distal to the incision to retract. A pedicle (Fig. 21.7) or bridge flap (Fig. 21.8) may be considered as alternatives. A bridge flap may be created with a narrow band of conjunctiva that runs across the corneal lesion allowing a greater view of the anterior chamber. Edges of the flap overlying the cornea are sutured with 10-0 nylon and those overlying episclera with 8-0 polyglactin 910 (e.g. Vicryl). Non-absorbable suture knots must be buried.

Pterygium surgery

Amit Patel, Carlo Enrico Traverso and Massimo Busin

A pterygium (from the Greek pterygion meaning ‘wing’) is a degenerative wing-like fleshy mass of bulbar conjunctival and subconjunctival tissue that arises at the limbus and encroaches onto the corneal surface (Fig. 21.9). It consists of an elevated leading edge (head) and a broad triangular fibrovascular mass (body). Although it most commonly originates from the nasal limbus, temporal or simultaneous nasal and temporal pterygia may occasionally exist. Histopathologically, it is characterized by fibrovascular proliferation and ‘elastotic degeneration’, i.e. positive to elastic tissue stain, but is not sensitive to elastase. In addition, there is alteration of the basal corneal epithelial layer, destruction of Bowman’s layer, and scarring of the superficial corneal stroma.

Although the precise pathogenesis of pterygia formation remains speculative, it is largely thought to be related to ultraviolet light exposure10,11. This is supported by its formation in the interpalpebral fissure as well as the higher prevalence among people living closer to the equator and in those with outdoor occupations. Ocular surface irritation from dust, sand, etc. has also been implied as a causative factor.

Surgical technique

The goals of pterygium surgery are to remove the lesion, restore the conjunctival anatomy, leave the cornea as smooth and clear as possible, and prevent recurrences. Historically there have been, and there continue to be, numerous techniques to manage pterygia. Techniques described include avulsion or excision of pterygia leaving either ‘bare sclera’, closure with conjunctiva (direct, sliding and auto-grafts) or amniotic membrane and use of peripheral lamellar corneal grafts. Various adjuncts (e.g. mitomycin C) have also been used in combination with the different techniques. The lack of consensus on the preferred surgical approach is due to recognition that no single surgical method has proven to be superior. The following will describe one widely used technique of pterygium excision and conjunctival transplant.

Primary pterygium

Peribulbar anesthesia is most commonly used; however, the procedure may also be performed under topical and/or subconjunctival anesthesia. An eyelid speculum providing good exposure is placed and a limbal traction suture (6.0 silk or polyglactin 910 on a spatulated needle) may be placed at the 12 or 6 o’clock position, or both, to allow more extensive globe rotation and aid rectus muscle identification.

The outline of the pterygium is marked with a gentian violet marker, and anesthetic or balanced salt solution is injected subconjunctivally to balloon the pterygium (Fig. 21.10A). This allows easier dissection and protects the underlying rectus muscle from accidental damage.

The head of the pterygium is lifted with fine toothed forceps and gentle dissection using a rounded sharp blade (e.g. Beaver No. 57) or Tooke’s knife is employed to roll the tissue towards the limbus (Fig. 21.10B). A superficial keratotomy may be made to outline the leading edge prior to the dissection and a superficial plane of dissection is maintained up to the limbus. Attempts must be made to maintain a level and smooth plane of dissection. On reaching the limbus, the bulbar portion (body) of the pterygium is then excised carefully down to the sclera using Wescott scissors. Particular attention should be paid in dissecting and removing all the underlying Tenon’s tissue. To minimize the risk of recurrence, this dissection should lead to complete removal of all the hypertrophic fibrotic tissue underlying the pterygium and must be carried out up to the recti perimysium, into which it usually blends. The gentian violet marks allow visualization of the margins following the subconjunctival injection and avoid inadvertent excision of the plica semilunaris and caruncle. Wet field cautery may be applied sparingly to achieve hemostasis. Remnant tissue at the limbus and sclera is scraped using a rounded blade or large diamond burr.

The rolled edges of the remaining conjunctiva are unraveled with forceps, and the conjunctival defect is then measured with calipers. The globe is rotated upward with the limbal traction suture and the inferior bulbar conjunctiva away from the pterygium excision is exposed. In general, it is advisable to spare the superior conjunctiva, in case filtration surgery is needed later in life. A limbal edge is preferred and a gentian violet marker is used to mark the outline of the remaining three sides of conjunctival graft to be created (Fig. 21.10C). The conjunctiva is dissected from the underlying Tenon’s tissue by injecting 1–2 ml of local anesthesia (e.g. 1%–2% lidocaine) with a 27-gauge needle. The injection site should be situated away from the conjunctival graft intended for use so as to prevent creating a buttonhole. A small incision is made just peripheral to the superior corner of the marked area. Blunt and sharp dissection is performed with Wescott scissors and non-toothed forceps to ensure that the conjunctiva is separated from Tenon’s, ideally in the plane created by the local anesthesia. The dissection is carried out in a meticulous fashion to the limbus and care is taken to avoid buttonholes. Once the conjunctiva is dissected free from the underlying Tenon’s, the edges of the graft are cut slightly larger than the outline marks. This allows for the natural tissue shrinkage and also incorporates the gentian violet marks, which are useful in aiding graft orientation.

Once the graft is totally free, the area to be grafted is re-examined to make sure it is clear of significant clot or active bleeding. The ocular surface is moistened with balanced salt solution and fine non-toothed forceps are used to slide the graft onto the bare area ensuring that the epithelial side remains up and the limbal areas correspond. The risk of tissue rolling, incorrect orientation and excessive manipulation is minimized by sliding the graft and thus lifting it off the eye should be avoided.

Once the edges of the graft are approximated to the edges of the bulbar conjunctiva, absorbable sutures (e.g. polyglactin) are used to secure the graft. The first sutures are positioned through the two limbal corners of the graft, into sclera, and then into conjunctiva to place the limbal edge of the graft on gentle stretch. If the limbal edge is on good stretch, no additional sutures are required. The next two sutures secure the posterior corners of the graft to the bulbar conjunctiva. Additional sutures are placed to close the wound edges and horizontal mattress sutures may be used to anchor the edges to the underlying sclera (Fig. 21.10D). It is important to suture the graft to conjunctival edges, and not just Tenon’s, as these two tissues may appear similar. A wet swab may be used to distinguish between the two, as Tenon’s tends to stick to the swab whereas conjunctival tissue does not. The conjunctival defect in the area from which the graft is harvested may be sutured, but is usually allowed to re-epithelialize spontaneously. Suture knots are not generally buried and any buttonholes are sutured and anchored to the underlying sclera.

Recurrent pterygium

Recurrent pterygia pose an increasing challenge to the surgeon as they usually exhibit more conjunctival inflammation and aggressive fibrovascular growth compared with primary pterygia. The normal anatomy is disrupted from previous surgery and the resultant fibrovascular scarring. Furthermore, there may be associated corneal scarring and/or thinning, limited ocular motility, and limbal stem cell deficiency.

The additional scarring results in increased intraoperative bleeding and risk of damage to the underlying rectus muscle which may be adherent to the recurrent pterygium. Thus caution should be taken to lift the pterygium prior to dividing any tissue. It is imperative to identify and hook the rectus muscle whilst excising the recurrent tissue. Vasoconstrictors may be used to reduce intraoperative bleeding and cautery must be applied judiciously in order to avoid muscle and scleral damage.

If a conjunctival graft was performed during the previous operation, the same quadrant of bulbar conjunctiva may be difficult to dissect and fashion into another graft. In such cases, and especially when there is limbal stem cell deficiency, a graft may be taken from the fellow (uninvolved) eye. This possibility needs to be discussed with the patient prior to surgery. Amniotic membrane may be used as an alternative in such cases or in patients with glaucoma in whom it is important to preserve the superior conjunctiva. Alternatively, the area of bare sclera corresponding to the excision may be allowed to re-epithelialize spontaneously.

Residual corneal opacities may be treated with photo therapeutic keratectomy (PTK). Lamellar keratoplasty may be required in the presence of significant corneal scarring or thinning to achieve visual rehabilitation and reduce recurrence12.

Postoperative care

Postoperative care includes topical antibiotics and corticosteroids. Initially, ointments are preferred over drops 4–6 times a day as they tend to be more comfortable. A therapeutic bandage contact lens may also be applied. Once both corneal and conjunctival re-epithelialization is completed, the medication can be changed to corticosteroid drops, which are tapered slowly over several weeks. Non-absorbable sutures, if used, should be removed between 3 and 6 weeks postoperatively.

During the first two postoperative weeks there is often significant edema of the conjunctival graft. Continued frequent use of topical corticosteroids leads to resolution of the edema, which does not affect graft survival as long as the sutures holding the conjunctival transplant do not loosen prematurely. Significant graft swelling can cause dellen formation, which needs to be treated with aggressive lubrication.

Conjunctival or corneal infections may develop after surgery and should be treated with aggressive topical therapy as appropriate following swabs for microbiology cultures.

Large buttonholes, poor wound apposition, and cheesewiring of sutures due to excessive tension on the graft increase the chances of early graft healing problems. Graft dehiscence may also occur due to infection or loose sutures and may require re-suturing or replacement.

Complications which are generally not debilitating or sight threatening include astigmatism, graft retraction, inclusion cysts, suture granulomas, and hematomas.

The most common complication of pterygium surgery is recurrence. Adjunctive therapies may be applied at the time of recurrent pterygium excision. Although beta radiation, thiotepa, daunorubicin, etc. have been used previously, mitomycin-C application remains popular due to evidence of reducing recurrence. However, the lack of consensus on the precise dose and duration of application, together with the potential adverse effects including scleral perforation, limit its use and call for precautions.

Other significant complications include corneal irregularity and scarring, excision-induced limbal stem cell deficiency, restriction of ocular motility, rectus muscle disinsertion, and infection.

Excimer laser phototherapeutic keratectomy

Angelo Macrì and Carlo Enrico Traverso

Excimer laser phototherapeutic keratectomy (PTK) has been performed to treat anterior corneal pathology for the last 20 years. FDA approved PTK in 199513. Since then indications and techniques have continuously evolved.

Stromal lesions

Dystrophies of Bowman’s layer, such as Reis–Bucklers dystrophy, and stromal dystrophies, such as granular or lattice dystrophy, are the main indications.

Best results are obtained when the opacities are in the anterior 20% of the cornea. It is a general opinion that PTK may be tried in all patients with dense superficial opacities before undergoing a more invasive procedure, such as lamellar or penetrating keratoplasty13,19.

Corneal haze after excimer laser corneal surgery

The most important predictive factor in haze formation has been reported to be the depth of ablation that is linked to the attempted dioptric correction. This could be related to surface irregularities that impede normal corneal repair when higher corrections are performed. In theory PTK could be very useful in preventing haze by obtaining a smoother surface after PRK.

PTK can be also used to treat late haze and subepithelial scarring after PRK (Fig. 21.11). In both cases MMC is utilized because predominant effect of MMC in blocking haze formation was at the level of profound inhibition of the replication of keratocytes and myofibroblast progenitor cells in the corneal stroma that occur following the normal keratocyte apoptosis response to epithelial removal during surface ablation.

Although its utility and efficacy for haze prophylaxis are well documented, the long-term safety profile of MMC use in refractive surgery is not known and it is still used in an off-label fashion.

Technique

The technique varies according to size, shape, density, and numbers of the cornea lesions (Figs 21.12 and 21.13).

Thus it can be used for:

Elevated lesions are generally debulked with a blade before PTK.

The epithelium is generally mechanically removed if loose and irregular, while it is left in place before PTK if it is smooth, because may act as an effective masking agent.

Modulating agents such as artificial tears, also called masking fluid, can be very useful in achieving a uniform corneal surface. For this purpose, variable mixtures of hyaluronic acid solutions were proposed.

The treatment is stopped several times to check, also at the slit lamp, the progress of photoablation.

PTK can be also performed topographically guided or ‘customized’13,21.

Intraoperative mitomycin C (MMC) can be used after PTK to try to decrease postoperative haze and recurrence.

Commonly MMC is used at 0.02% (0.2 mg/ml) concentration, on a 6–8 mm circular sponge for 60 seconds; it is then irrigated with 30 ml of saline13,20,22. Other regimens are also suggested.

Summary

PTK is a very versatile technique that is quite effective at treating a wide variety of anterior corneal lesions (Figs 21.14 and 21.15) with a low risk rate if performed properly. In particular elevated lesions and opacities in the top 10–20% of the corneal stroma generally do very well. If unsuccessful, an anterior lamellar graft can almost always be performed and thus PTK may be tried before proceeding to a corneal transplant, considering its excellent risk/benefit ratio13.

Corneal transplantation

Massimo Busin, Amit Patel, Davide Venzano and Carlo Enrico Traverso

Historical perspective

There is considerable debate regarding who first came forth with the concept of replacing diseased or scarred corneas with living tissue. Guillaume Pellier de Quengsy first suggested replacing the diseased cornea with a thin glass disc (similar to a keratoprosthesis) in 1789, and Erasmus Darwin, grandfather of the famed Charles Darwin, first suggested replacing a scarred cornea with a small piece of living donor corneal tissue. Franz Reisinger published the results of his experiments on corneal transplantation in rabbits and chickens in Germany in 18242325. S.L. Bigger successfully replaced the scarred cornea of his pet gazelle with a healthy donor cornea from another gazelle in 183724. Richard Kissam, a New York ophthalmologist and general practitioner, was the first to operate on a human using a pig donor cornea; however, the graft became opaque shortly thereafter24. The advent of ether and chloroform inhalation anesthesia, topical cocaine anesthesia, local infiltrative anesthesia, and antiseptic surgery during this early period revolutionized corneal transplantation, as it also did for many other types of surgery.

These important companion discoveries were undoubtedly instrumental in accelerating the progress of corneal transplantation. Considerable amounts of experimental work using living corneal grafts ensued. Von Hippel was the first to improve vision with LK, consisting of a full-thickness rabbit donor cornea placed into a human recipient lamellar bed24. He was also the first to use a circular trephine. In 1906 successful total penetrating corneal graft in a human was reported by Zirm in a laborer with bilateral lye burns to the cornea26. Ironically, alkali burns like this are now known to have one of the worst transplantation prognoses. Anton Elschnig of Prague, with his extensive experimental and clinical work in the 1920s through the 1930s, is credited with refining the crude technique into an elegant, reliable procedure. Filatov, Tudor Thomas, Paton, Franceschetti, Paufique, Sourdille, Castroviejo, Arruga, and the Barraquer brothers, all eminent surgeons, based much of their knowledge and methodologies on the foundation laid by Elschnig24. Ramon Castroviejo, a Spanish ophthalmologist practicing in New York City, initiated detailed grafting methodologies, expounding the use of the square graft (Fig. 21.16), and developing and refining keratoplasty instrumentation. A. Edward Maumenee extensively studied the immunology and physiology of corneal graft rejection. Claes H. Dohlman came to the United States from Sweden and established the first cornea fellowship program in 1961, emphasizing the importance of both clinical and research training. With more recent ophthalmological advances consisting of microscopic surgery, inert sutures, antiviral and antibiotic medications, topical and systemic corticosteroids, tissue-preservation/eyebanking strategies, and progress in immunology, the success of corneal transplantation has grown rapidly over the last 30 years. Paralleling these advances, clinical indications for corneal transplantation surgery have also expanded considerably.

The last decade witnessed a strong expansion in the use of lamellar techniques.

The anterior lamellar keratoplasty performed with deep stromal separation, described by Melles (DALK) enables the surgeon to leave the recipient with healthy endothelium, with good visual results27,28.

Endothelial decompensation being the leading indication for PK procedures2934, there has been strong interest in developing a technique able to preserve the healthy recipient stroma.

Since the original description of the posterior lamellar keratoplasty (PLK) described by Tillett and Barraquer in the 1950s and 1960s, in 1999 Melles demonstrated the first sutureless PLK35. Since then, numerous modifications in surgical technique and new instruments have led to increasing popularity of PLK.

Indications

Indications for keratoplasty have varied over the decades3638. Box 21.1 lists the classical indications for PK; today many of these conditions may be effectively treated with LK. The Eye Bank Association of America recorded over 41 000 transplants performed in the United States in 2008, with a simultaneous increase in grafts provided for endothelial keratoplasty38. Whilst keratoconus and aphakic bullous keratopathy were major indications for corneal transplantation three decades ago, pseudophakic bullous keratopathy (PBK) rapidly emerged as a leading indication in the 1980s and 1990s3841. This coincided with the dramatic increase in the number of cataract extractions performed. Optical indications for transplantation include corneal decompensation (e.g. bullous keratopathy and endothelial dystrophies), ectasia (e.g. keratoconus), scarring (e.g. traumatic, post-infectious or iatrogenic), and stromal dystrophies. Tectonic indications (e.g. melting, descemetoceles, perforation) are aimed primarily at preserving globe integrity and may allow optical improvement simultaneously or at a later stage. Therapeutic indications (e.g. medically unresponsive infections) provide the two-fold advantage of excisional biopsy and of elimination of the infected tissue. Causative organisms in these cases are often fungi or acanthamoeba, however, common pathogens causing microbial keratitis may also necessitate therapeutic keratoplasty.

Eye banking/donor selection

The first successful human corneal transplant by Eduard Zirm in 1905 involved the use of fresh corneal tissue from a boy whose eye was enucleated for a penetrating sclera injury. For approximately the following 30 years, all human keratoplasties were performed using fresh corneal tissue from living donors whose eyes had been enucleated due to trauma or disease not involving the anterior segment. In 1937, Filatov from the Ukraine introduced the use of whole globes from cadavers stored at 4°C in a moist chamber. Paton established in the US the first eye bank that involved procurement, processing, and distribution of donor corneas37.

Today, cold storage, organ culture, or cryopreservation may be used to preserve the corneoscleral buttons. Cryopreservation allows the tissue to stay viable at –70°C for more than 1 year; however, this is seldom used as it is expensive and technically complicated. Both the freezing and thawing procedures in this technique demand fastidious timing and special precautions to avoid damage to endothelial cells.

Thus, cold storage and organ culture are the two main methods for preserving the donor tissue today. Cold storage (2–6°C) was introduced in 197442,43, and is commonly used in the USA. The technique is relatively simple and involves refrigeration with minimal tissue handling. No complex equipment is required. At 2–6°C, the metabolic activity of the endothelial cells is minimal and therefore deturgescent agents (e.g. dextran or chondroitin sulfate) are required to keep the cornea in a relatively dehydrated state and thus maintain corneal thickness. The original McCarey-Kaufman (M-K) medium has been modified with addition of antibiotics, energy sources, antioxidants, growth factors, and membrane stabilizing agents to improve cell survival, reduce autolysis, and maintain ultrastructural integrity. Although endothelial cell loss may be attributable to numerous factors independent of storage technique, corneas stored at 2–6°C show intercellular disruption, reduced cell adhesion as well as endothelial cell loss and death44. Modified storage media have increased the storage time for up 2 weeks, one week being most often recommended. Organ culture (31–37°C) was introduced in 197645 and is commonly used in Europe. During the storage phase in culture medium supplemented with fetal or newborn calf serum, antibiotics and antimycotics, the corneas swell considerably and can reach twice the normal thickness. Dehydrating molecules are not added as they are ingested by the corneal cells and lead to toxicity. Thus, a shorter second phase is required to reverse the swelling prior to transplantation. Dextran (4–8%), is added to the same medium to facilitate de-swelling and transportation. This phase in transport medium varies between 1 and 7 days. Overall, organ culture allows for longer periods of storage (up to 4–5 weeks). Advantages over cold storage include ease of scheduling surgery, allowing time for tissue typing/matching, and more rigorous microbiological testing.

Regardless of the storage methods used, donor and tissue evaluation to assess suitability is critical. It includes obtaining a thorough medical and social history of the donor as well as serological testing, slitlamp biomicroscopy, and endothelial cell examination. The tissue is evaluated for epithelial integrity, epithelial and stromal opacities, presence of foreign bodies and infectious infiltrates, evidence of previous anterior segment surgery, degree of stromal clarity and thickness, presence of Descemet’s membrane folds and extent of endothelial guttae, snail tracks, and precipitates. Specular microscopy provides detailed microscopic analysis of individual cell morphology and an estimate of cellular density (Fig. 21.17A), however for a better and wide examination light microscopy is applied (Fig. 21.17B). The cell counts may be obtained by automated image analysis or manual counting methods.

Donor tissue has to be considered as non-sterile and effective decontamination must be in the routine. Antibiotics are less effective in cold storage than organ culture as the contaminating microbes are metabolically less active at low temperatures. For this reason, preoperative warming of the storage media is important to enhance the decontamination effect. Individuation of microbial contamination may also be better with organ culture since contamination will become more readily evident and it may therefore be considered as the storage method of choice in circumstances where corneas are suspected of being at a higher risk of contamination. However, stringent screening protocols by eye banks have minimized the risk of microbial transmission from donor to recipient and the accurate valuation of medical and social history of the donor allowed rare incidences of systemic disease like rabies, hepatitis B, Creutzfeldt–Jakob disease (CJD) and malignancies4448. No case of seroconversion after unplanned transplantation of corneas from human immunodeficiency virus (HIV) positive patients has been reported to date4951.

Irrespective of the storage methods, prospective studies analyzing short and long-term follow-up after PK have not found any difference in endothelial cell density or clinical outcomes5254.

Preoperative evaluation

History

Taking a careful and detailed clinical history is of paramount importance during the preoperative evaluation. Information about the pre-morbid visual acuity may elucidate the chronology of the visual deficit, and may provide information on amblyopia, retinal disease, glaucoma, and optic neuropathy. A history of iritis, glaucoma, trauma, dry eyes, herpetic infection, and previous operations may require alterations of surgical technique and postoperative care.

A history of the patient’s general health and demeanor must be assessed concomitantly, and is helpful in planning the anesthesia. Cardiac, pulmonary, and endocrinological disease may require specific anesthetic precautions. The patient’s systemic medications may influence blood coagulation, wound healing, and tear production. The mental status of the patient must also be assessed, as keratoplasty is relatively contraindicated in patients with severe mental retardation, psychosis, alcohol and drug addiction, as well as those at risk of self-inflicted trauma and poor compliance.

A history of allergies to some medications may preclude the use of certain intraoperative and postoperative medications. The patient’s present and anticipated future activities of daily living (e.g. employment, hobbies, and environment) from a visual and physical standpoint should be assessed. Those who engage in contact sports or work in high risk environments for eye trauma may need to drastically alter their lifestyles if they wish to undertake PK. The individual’s visual needs, as well as visual difficulties, are important factors to consider in the final surgical plan, especially when deciding the type and timing of the surgery.

Examination and investigations

The clinical examination begins with a comprehensive visual assessment consisting of visual acuity measurement and refraction for both distance and near. Additional testing as color vision, B-scan ultrasonography, electrophysiological tests, swinging light test, visual fields, retinal angiography, and ocular coherence tomography (OCT) or ultrasound biomicroscopy may aid in excluding retinal and optic nerve related causes of visual dysfunction. However, in the presence of opaque media, some of these tests may not be performed reliably. If the corneal pathology is primarily refractive in nature (e.g. keratoconus or scar-related corneal astigmatism), additional useful testing includes corneal topography. Anterior segment OCT or Schiempflug may be useful to ascertain depth of stromal scars or deposits prior to decide the type of surgery. In cases of endothelial dysfunction, often bilateral, specular microscopy and pachymetry may be useful in assessing progression and extent of disease for the careful scheduling of the therapy A thorough adnexal examination must be carried out and any eyelid and/or lacrimal problems, such as blepharitis, rosacea, scarring, lagophthalmos, ectropion, entropion, floppy eyelid syndrome, trichiasis, and epiphora need to be appropriately treated prior to corneal surgery. A detailed slit-lamp biomicroscopic examination should search for tear film abnormalities, conjunctival scarring (seen in cicatricial conditions such as Stevens–Johnson syndrome, ocular cicatricial pemphigoid or after chemical, radiation and thermal burns or in severe atopic disease, and in case of previous conjunctival surgery), corneal staining or vascularity, and anterior chamber abnormalities (e.g. synechiae and iritis). The presence of these findings may contribute to a poor prognosis or even contraindicate surgery. Corrective surgery or medical therapy prior to surgery may help to improve the outcome of surgery in such cases. Limbal stem cell transplantation may be considered prior to surgery in those with limbal stem cell deficiency (e.g. congenital aniridia, chemical burns).

The status of the crystalline lens or the IOL should be assessed to ascertain the need for concurrent cataract extraction or IOL repositioning, explantation, or exchange. Preoperative biometry may not be as predictive of the final refractive status when IOL implantation is combined with PK as when it is performed in the absence of corneal disease or surgery. A combination of good clinical judgment, measurements from the other eye, reasonable choice of IOL formulas, and personalization of equations using regression analysis to estimate the surgeon’s refractive tendencies, may enhance the predictability; high refractive errors are still occurring in combined PK/IOL cases55,56.

The decision to render the eye myopic, emmetropic, or hyperopic should be influenced by the patient’s need, and the refractive status of the contralateral eye. In general, a final myopic error will lend itself better to further correction with laser or surgical treatment. The condition of the iris/iridocorneal angle and integrity of the capsular bag may be a determinant of the type of IOL to be implanted. Alternatively, the eye may be left aphakic, with view to secondary IOL implantation at a later stage. This may yield better postoperative refraction and unaided visual acuity but delays visual rehabilitation and risks damage to the graft57,58.

The presence of glaucoma in eyes needing corneal transplantation must have optimal control both prior and following surgery.

Setting realistic expectations for the patients prior to surgery is important. The patient must be counseled before surgery, and informed of the realistic time span for visual rehabilitation. Those undergoing PK may expect one year or longer to achieve maximal potential. Lamellar surgery may provide a faster rehabilitation. In either case, they may require refractive correction in the form of spectacles, contact lenses, or refractive surgery. The risks of rejection and infection together with the need for suture removal/adjustment must be reiterated. Patients who are well informed are generally happier and more likely to comply with the rigorous postoperative management.