Coats of the eye

The conjunctiva is adherent to the sclera at the limbus, so the radial incisions to enter the subconjunctival plane have to be made just behind the limbus. The conjunctiva becomes friable with age and care must be taken to avoid tearing and buttonholing. Nontoothed forceps (such as notched forceps) are used to grasp the conjunctiva.

Tenon’s capsule is a layer of fascia that envelops the globe from the limbus to the optic nerve (Fig. 100.1). It is pierced by the extraocular muscles. A glove-like sleeve of fascia extends anteriorly (to the rectus insertions) and posteriorly (for several mm) along the muscles from the points at which they pierce Tenon’s capsule. Between the rectus muscles anteriorly these sleeves are joined by a layer of fascia: the intermuscular septum. The intermuscular septum and fascial sleeves of the recti are sometimes collectively referred to as the posterior Tenon’s capsule. The result of this complex arrangement is that several layers of tissue have to be incised to get access to the surface of the sclera (or sub-Tenon’s space). The anterior Tenon’s capsule may be dissected away from the sclera along with the conjunctiva (to which it is adherent by small fascial filaments). The intermuscular septum is then divided separately. Care must be taken when stripping fascia off the rectus muscles because ligaments from the recti to the wall of the orbit are functionally important in the actions of the muscle.⁷

Fig. 100.1 Tenon’s capsule. (a) Conjunctiva and (b) anterior Tenon’s have been dissected to reveal the (c) “posterior Tenon’s” glove-like extensions of tenons capsule along the recti and the associated intermuscular septum. Bare sclera (d) lies under this.

The thickness of the sclera varies. It is thickest around the optic nerve (1.2 mm) and thinnest under the recti behind their insertions so attempts to pass scleral sutures under the muscles are particularly hazardous. Where scleral mattress sutures are more typically passed, at the equator, it is approximately 1 mm thick. Passage of sutures is facilitated by the lamellar arrangement of collagen fibers, which allows spatulated (or “side cutting”) needles to follow a plane between lamellae.

Extraocular muscles

The recti are adherent to the sclera at the spiral of Tillaux. The location of this ring corresponds approximately to that of the ora serrata (Fig. 100.2).⁸ Circumferential scleral tires are therefore often placed as anteriorly as the rectus muscle insertions will allow. In this position they support the retina as far anteriorly as the ora serrata (“break ora occlusive buckling”).

Fig. 100.2 The ora serrata and the spiral of Tillaux (rectus insertions). The sclera has been rendered transparent to reveal the relationship between the ora serrata and the muscle insertions. Buckling anteriorly as far as the rectus insertions prevents anterior leakage.

The superior oblique muscle runs laterally from the trochlea to its insertion under the superior rectus. Passage of a superior rectus muscle hook from the temporal side of the muscle reduces the risk of inadvertently “hooking” the superior oblique as well as does keeping the sweep of the hook pre-equatorial. The superior oblique insertion is frequently encountered on the temporal side of the muscle where it can be an obstacle to scleral suturing. Division of a small (<) portion of the insertion to facilitate suturing seems to have little effect on ocular motility. Note that a vortex vein is usually present under the temporal edge of the superior oblique insertion.

The inferior oblique muscle passes under the lateral rectus muscle. The chance of inadvertently hooking it while passing a muscle hook under the lateral rectus is reduced by passing the hook from the superior side.

Choroidal vasculature

The long posterior arteries (as well as their corresponding nerves) run anteriorly from the equator at 3 and 9 o’clock and may be damaged by heavy photocoagulation or subretinal fluid drainage in these meridia (Fig. 100.3, available online).

Fig. 100.3 The choroidal vasculature. Surgical trauma should be minimized to all of these structures. A, anterior ciliary artery; B, long posterior ciliary artery; C, vortex ampulla; D, vortex vein; E, greater arterial circle of the iris.

The anatomy of the vortex veins is somewhat variable but one tends to leave the globe either side of the vertical recti just behind the equator. They may be inadvertently hooked along with a vertical rectus muscle if the muscle hook is passed behind the equator. Injury to the vortex veins may result in interruption to the venous drainage from the choroid and choroidal detachment. When operating near the vertical recti the vortex veins should be identified to prevent injury.

The choriocapillaris itself is very vascular and prone to bleed when penetrated. Because the vortex veins tend to be located near the vertical recti subretinal fluid drainage is carried out closer to the horizontal than to the vertical recti whenever possible.

The anterior ciliary arteries are useful indicators of the meridia of the rectus muscle insertions (Fig. 100.4). As they supply the arterial circles of the iris surgical trauma (including diathermy) should be minimized.

Fig. 100.4 The anterior ciliary arteries. A useful indicator of the location of the rectus positions especially in reoperations. Note that the lateral rectus only has one.

Innervation

Sensory nerves from the globe and bulbar conjunctiva pass through the ciliary ganglion. Local anesthesia in this region, for example, sub-Tenon’s anesthesia, will therefore anesthetize the globe effectively. The innervation of the lids and palpebral conjunctiva is by the lacrimal, frontal and infraorbital nerves, which do not pass through the muscle cone. Blockage of the ciliary ganglion alone does not therefore reliably provide adequate analgesia for buckling surgery.

Finding the retinal break

Missed retinal breaks are an important cause of surgical failure so the preoperative examination should be very thorough.⁹ Even when a break has been found, it is essential to complete examination of the retina, as most retinal detachments have more than one break.¹⁰ Their location is carefully documented on a chart that can be referred to subsequently during surgery (Fig. 100.5). These drawings should show the location of retinal breaks in relation to easily visible retinal landmarks such as small hemorrhages, vascular bifurcations, and areas of pigmentation.

Fig. 100.5 A retinal drawing – note the emphasis on easily visible features that can act as guides to the location of breaks intraoperatively.

This carefully documented preoperative assessment has many advantages. If in doubt, an area of retina can be re-examined alternately with indirect ophthalmoscopy and slit lamp biomicroscopy to establish whether a break is truly present. The drawings made can be referred to if the retinal view becomes obscured during surgery. If the breaks are not easily seen the other retinal features on the drawings provide useful reference points to their location.

In children and uncooperative patients, it may be impossible to establish the position of the retinal breaks preoperatively. One is then forced to rely on the intraoperative examination under anesthesia.

Lincoff’s rules

Lincoff has shown how the location of retinal breaks determines the distribution of subretinal fluid (Fig. 100.6).¹¹ Review of the retinal drawings will therefore determine whether the break location is consistent with the subretinal fluid distribution. When the distribution of fluid does not seem to obey Lincoff’s rules reexamine the retina to ensure that no breaks have been missed.

Fig. 100.6 The location of retinal breaks can be deduced from careful analysis of the topography of the detachment as described by Harvey Lincoff. (A) An inferior detachment slightly higher on the temporal side pointing to a break on that side. (B) A subtotal retinal detachment – the break is usually close to the upper border of the fluid on the side it is highest. (C) The fluid crosses the midline superiorly implying a superior break near 12 o’clock. The fluid has tracked down further nasal implying the break is slightly to the nasal side. (D) The presence of bullae implies a superior break. A shallow sinus of fluid leads to a small superonasal break.

Scheduling surgery

In “macular on” retinal detachment, urgent surgery should generally be scheduled to prevent detachment of the macula. Cases with tractional tears tend to progress very rapidly and should be treated urgently. Asymptomatic retinal detachments and detachments without tractional breaks (e.g., those due to retinal dialyses, atrophic retinal breaks in young myopes and cases with “tide marks”) progress more slowly. Some delay, if it allows optimal conditions for surgery, may then be acceptable.

Reducing eye and head movements seems to reduce the rate at which subretinal fluid accumulates. Bed rest, eye patching and rectus sutures have all been used to reduce the amount of subretinal fluid. This may prevent extension of subretinal fluid to the macula and make it easier to identify retinal breaks. It may also avoid the need for subretinal fluid drainage.¹² Such measures are rarely practical now, as most retinal detachment care takes place in an ambulatory or semi-ambulatory setting.¹³

Anesthesia

General anesthesia provides ideal operating conditions for younger patients, uncooperative patients and for reoperations (when local anesthesia may be less effective).

Peribulbar administration of a 50 : 50 mix of lidocaine and bupivacaine, particularly when used with adjunctive Hyalase, provides excellent anesthesia and akinesia. Its action is not limited to the nerves which travel in the muscle cone or sub-Tenon’s space.

In theory, sub-Tenon’s anesthesia alone should be insufficient (see above). In practice, sub-Tenon’s anesthesia gives anesthesia equivalent to other techniques,¹⁴ presumably due to overspill of anesthetic agents to the peribulbar space. A particular advantage of sub-Tenon’s anesthesia is the ease with which it can be “topped up” intraoperatively.¹⁵ Sub-Tenon’s anesthesia may also be a useful adjunct to general anesthesia¹⁶ both to block the vagus (preventing bradycardia or asystole from rectus muscle traction) and for analgesia in the immediate postoperative period. The presence of buckles and scarring may make this technique more difficult and less effective in reoperations.

Positioning the head for surgery

Surgical access is best when the orbital rim is horizontal. This is achieved by extending the neck slightly and tilting the nose away from the operated eye (Fig. 100.7, available online). Once in the correct position the head may be fixed with a loop of clinical adhesive tape.

Fig. 100.7 Improving surgical access by flattening the orbital rim: (A) extension of the neck; (B) slightly tilting the head.

Preparation and draping

The skin and lashes are cleaned with a disinfecting solution such as povidone iodine. A diluted aqueous iodine solution can be instilled in the conjunctival sac (avoiding the use of undiluted or alcohol-based preparations for this). The skin should be thoroughly dried before application of a sterile self-adhesive drape. Providing these steps are taken it should be possible to tuck the eyelashes under the lid when the lid speculum is introduced and it is therefore unnecessary to trim the lashes preoperatively.

If the palpebral aperture is deemed too narrow a lateral canthotomy may be performed.

Conjunctival peritomy

Neat incisions with later anatomical reposition of the conjunctival edge prevents a number of unpleasant sequelae. Conjunctival misalignment with heaped scars may cause tear film dysfunction. Buttonholing the conjunctiva may lead to Tenon’s prolapse and delay healing. Recession of the peritomy edge leaves bare sclera and makes subsequent reoperation difficult.

A circumferential limbal peritomy with radial relieving incisions is made.¹⁷ The conjunctiva 3–4 mm behind the limbus is grasped with forceps and gently lifted creating a radial pleat of conjunctiva (Fig. 100.8). A blunt-tipped spring scissors is used to make a vertical radial cut. A second cut is often needed to extend the incision through Tenon’s capsule down to the sclera. Great care is taken not to tear the conjunctiva. The spring scissors can easily be used in either hand and the orientation varied as the incision progresses. A gentle spreading action of the scissors under the conjunctiva breaks the weak trabecular adhesions to the episcleral tissue.

Fig. 100.8 Limbal peritomy. (A) The conjunctiva is grasped with a nontoothed forceps and elevated to create a pleat. Radial division of this with spring scissors initiates the peritomy. (B) Spreading action with blunt scissors to break the trabecular adhesions to the sclera. (C) Extension of incision around the limbus. (D) 180° peritomy for segmental buckle.

A slight modification of this technique with the circumferential incision 2 mm behind the limbus leaves a frill that may be useful during closure (Fig. 100.9).

Fig. 100.9 A 180° peritomy with a 2-mm limbal frill of conjunctiva to facilitate closure.

The extent of the peritomy depends on the size of the buckle planned. A 360° peritomy is not required if a local explant is planned. Note that it is not necessary to perform a 360° peritomy purely to sling all four muscles as rectus bridle sutures can be passed transconjunctivally.

Slinging rectus muscles

Between two and four rectus muscles are slung depending on the planned size of the buckle.

A closed pair of blunt scissors is pushed though the intermuscular septum between two recti. The opening created is enlarged by spreading the blades (Fig. 100.10). In this way, the sub-Tenon’s space is opened and bare posterior sclera is exposed.

Fig. 100.10 Opening the intermuscular septum by spreading with blunt scissors. This opens sub-Tenon’s space exposing the posterior sclera.

The muscle is engaged with a sweeping posterior and circumferential movement around the globe employing a specialized muscle hook (Fig. 100.11, available online). Very posterior “sweeps” risk damage to the vortex veins. Once a rectus has been successfully hooked the globe moves with the hook. If the muscle is inadvertently split a second hook can be passed from the opposite side of the muscle. The remaining anterior fibers of the intermuscular septum are now cut off or swept off. This dissection should be limited to the fascia required to visualize the sclera.

Fig. 100.11 Passage of muscle hooks to avoid the obliques – the lateral rectus from above (A) and the superior rectus from the temporal side (B).

A large braided (e.g., 2/0 silk) bridle suture is passed under the muscle. There are various ways of achieving this involving reverse passage of the suture under the muscle (to avoid engaging the tip in the sclera). Alternatively, a modified muscle hook with a threading eyelet at its tip can be used.¹⁸ These bridle sutures can be clipped to the surgical drape to position and stabilize the globe thereafter (e.g., while suturing). When free movement of the globe is desirable (e.g., when searching for breaks) the clips are released.

The sclera is now inspected for dark ectatic areas (Fig. 100.12). Suturing and even cryotherapy or indentation at these sites can be perilous so their early identification is essential.

Fig. 100.12 Scleromalacia. The sclera is examined for any areas of thin sclera at the start of surgery. Surgical manipulation is avoided in these areas because of the risk of scleral perforation.

Reoperations

Special precautions must be taken during revision surgery.

Adhesions are invariably present between the conjunctiva and sclera. A cutting action with the scissors is more effective than a spreading action in breaking these. Care must be taken to avoid delaminating into the sclera or buttonholing conjunctiva.

A fibrous capsule forms around old explants. Incising this capsule exposes the surface of the explant. The plane thereby opened up is useful for slinging rectus muscles. The muscle hooks are placed around the muscles over the explants before these are removed. The rest of the peri-explant capsule is then trimmed flush with the sclera. The sclera is often very thin in the bed of longstanding buckles, especially encircling elements. No attempt is made therefore to dissect capsule off the bed of the buckle. Particular care must be taken when dissecting the capsule from the very thin sclera under the rectus muscles. The scissors are gently lifted away from the globe while closing the blades.

Examination under anesthesia and break localization

A careful indented examination under anesthesia of the whole peripheral retina is now carried out to confirm the location of the retinal breaks. The preoperative drawings provide a useful reference if they are difficult to locate.

The location of each break is marked on the sclera. This essential step is carried out while the cornea is clear and allows planning of the rest of the operation. The sclera is indented under indirect ophthalmoscopic indentation using a fine (but not sharp) tipped instrument such as a Gass scleral indenter.¹⁹ Once the indent is seen to correspond to the position of a retinal break sustained (for several seconds) indentation is applied. The resulting transient scleral thinning produces a focal area of scleral translucency and the underlying choroid shows through. This point is then marked with very gentle diathermy or a surgical marker pen. If a marker pen is used the sclera is dried both before and after the application to prevent the dye spreading. Several marks are made for larger breaks.

Errors in break localization may lead to buckle malposition. Localization errors tend to be radial (i.e., determining how far back a break is) rather than circumferential (determining its clock hour). For example, if a retinal break is highly elevated (as in a bullous detachment) parallax errors may make the break seem more posterior than it truly is (Fig. 100.13).

Fig. 100.13 Break localization error. When breaks are highly elevated, they appear more posterior than they really are due to parallax. A, apparent location; B, actual location.

Parallax errors may be avoided by draining subretinal fluid and then reforming the globe with air (the DACE operation) (Fig. 100.14).^20,21 The view of the retina through the gas bubble can be challenging for those not experienced with this technique.

Fig. 100.14 Bullous retinal detachment: (A) managed with the DACE (drain air cryotherapy explant) procedure. (B) The operation starts with subretinal fluid drainage and air injection. This aids subsequent break localization.

Retinopexy

The indent from the explant closes retinal breaks but retinopexy is required to produce an enduring bond between the retina and the retinal pigment epithelium that will persist even if the indent disappears.²²

Retinopexy was initially achieved using diathermy in association with lamellar scleral dissection and scleral implants.⁴ Cryotherapy has supplanted diathermy because it can be performed without scleral dissection and the treatment can be monitored ophthalmoscopically. More recently photocoagulation has also been used.

Cryotherapy

The technique of cryotherapy is described in detail in Chapter 106, Prevention of retinal detachment. The aim is to produce freezing of healthy retina surrounding all the retinal breaks. The treatment is monitored using the indirect ophthalmoscope. When the indent from the tip of the cryoprobe is seen under a retinal break the cryoprobe is activated. After a few seconds one observes whitening of the retina. Smaller breaks can be treated with a single application. The break is seen as a darker area within the freeze and this is useful in confirming that the whole break has been treated. Larger breaks may need several applications. These are applied by working methodically around the edges of the break to ensure contiguous burns with minimal overlap (Fig. 100.15). Refreezing and freezing of the bare central RPE in large breaks are avoided to reduce the risk of RPE dispersion.²³

Fig. 100.15 Confluent cryotherapy burns with minimal overlap.

One can envisage the immediate tissue reaction as an ice ball expanding outwards progressively in every direction from the tip of the probe for as long as the cryoprobe is active. Some factors (the insulating effect of an intervening rectus muscle, the heat sink effect of the choroidal circulation) impede the development of a visible reaction on the retina. Others (reduced choroidal blood flow in high myopia, the insulating effect of intraocular gas) hasten the development of retinal freezing. The effect of subretinal fluid is particularly important.

In the presence of shallow subretinal fluid, the indentation of the tip of the cryoprobe approximates the pigment epithelium to the retina and both freeze almost simultaneously. If the breaks are more elevated the pigment epithelium cannot be apposed to the retina. Freezing of the pigment epithelium can then be clearly seen to precede freezing of the retina, sometimes by several seconds (Fig. 100.16). In this situation, what is the optimal end point of treatment: freezing of the pigment epithelium or the retina? This is a particularly important question given the concern about potential adverse effects of excessive cryotherapy on other tissues.^24–26 In an experimental model the adhesions produced by freezing of the retinal pigment epithelium alone lacked the microvillous interdigitations normally present between pigment epithelium and retina. The resulting chorioretinal adhesion was weaker than when the freeze was allowed to extend to the retina.²⁷ In practice, the chorioretinal adhesions that develop from freezing of the pigment epithelium alone seem to be sufficient. A further advantage of freezing the retina however, is that the “lighting up” of the retinal breaks is a useful confirmation that all the edges of the break have been treated.

Fig. 100.16 Cryotherapy in the presence of subretinal fluid. Freezing of the retinal pigment epithelium is seen to occur first (A). As the ice ball gets bigger freezing of the retina with lighting up of the breaks (B).

In the presence of bullous subretinal fluid, it may be impossible to approximate the retina to the retinal pigment epithelium. In this situation, subretinal fluid drainage is probably safer than very heavy cryotherapy which may cause severe postoperative vitritis.

The tip of the cryoprobe must be allowed to thaw completely before attempted withdrawal, otherwise choroidal hemorrhage and even scleral avulsion may occur.

Cryotherapy to the disc or macula (Fig. 100.17) occurs when the indentation from the shaft of the probe is mistaken for its tip (“shaft indentation”) (Fig. 100.18). This cognitive problem can be avoided by encouraging trainees to intentionally indent posteriorly (without actually activating the cryoprobe!) (Fig. 100.19). They then become familiar with the distinctive appearance of shaft indentation.

Fig. 100.17 Inadvertent cryotherapy to the posterior pole.

Fig. 100.18 Shaft indentation – the cause of posterior cryotherapy.

Fig. 100.19 The appearance of shaft indentation (right) compared with tip indentation (left).

Beginners find cryotherapy on anterior breaks challenging because the cryoprobe has a tendency to slip over the surface of the eye. This can be overcome with counter-traction from the bridle sutures on the opposite recti (Fig. 100.20). Alternatively, the cryoprobe is intentionally placed anterior to the break and the globe rotated using the tip of the probe. The pressure of the probe is then slightly released while the indent from the probe is viewed using indirect ophthalmoscopy. As the globe returns slowly to the primary position the tip indentation is seen to move. When the indentation of the tip is under the break a very small increase in the pressure applied stabilizes the globe and the cryoprobe is activated.

Fig. 100.20 Additional bridle sutures to stabilize the globe during treatment of large anterior breaks, e.g. a dialysis.

Choice of scleral explant

Knowledge of the location of all the retinal breaks and their elevation allows planning of the rest of the operation including the choice of scleral explant.

The aim of placing an explant is the creation of an indentation in the wall of the eye which provides adequate support to all the elevated retinal breaks. Areas of detachment where there are no breaks do not require support. Breaks in areas of attached retina can be treated with retinopexy alone.

Historically, a number of materials have been used in the manufacture of explants.³³ None of these seem to be as well tolerated as silicone rubber which is biologically inert and can be left in situ indefinitely.^6,34

Two types of cylindrical silicone explant are currently in regular use, solid silicone tires and silicone sponges consisting of air-filled cells (Fig. 100.21). Early silicone sponges had communicating air cells and an increased risk of infection³⁵ but this problem has been much reduced by the use of sponges with closed air cells.

Fig. 100.21 Various types of explant may be used. Solid silicone tires of various sizes and profiles (A–C) are trimmed to the desired size (D–F). Silicone sponges also come in various sizes (G,H) and may have a circular or oval cross-section (I). Watzke sleeves (J) are used with bands (K) and silicone tires to create encirclements (L).

Solid silicone is, for practical purposes, non-compressible. Silicone sponges, because of their cellular composition are easily deformable and compressible. When a sponge is initially sutured the sponge is compressed and the intraocular pressure rises. As the intraocular pressure subsequently falls to physiological levels the sponge expands facilitating closure of elevated retinal breaks. (Details of the mechanism of action of scleral buckles are described in Chapter 99, The effects and action of scleral buckles in the treatment of retinal detachment.)

The height of the indentation produced by an explant is a factor of the bite separation and the diameter of the explant. Silicone tires are generally thinner than sponges and therefore produce lower indents. When used to treat elevated breaks an adjunctive measure such as subretinal fluid drainage or gas injection is more likely to be necessary if a circumferential tire is used.

The profile of the resulting indent also differs. Tires tend to produce broad indentation of uniform, albeit relatively low height. Sponges, particularly those with a circular cross-sectional profile, are much higher centrally. Accurate localization in the transverse meridian is therefore critical when using a sponge with a circular cross-sectional profile.

The design of solid silicone tires reflects their original use as circumferential scleral implants. There is a groove on the upper surface with a rectangular profile to accommodate an overlying band. It was subsequently found that they can be used as explants.³⁶ Some surgeons dispense with the band and use them as purely local explants.

Silicone tires are usually oriented circumferentially. Sponges may be oriented either circumferentially or radially. The geometry of the indent favors radial orientation of sponges when treating retinal tears.² While the choice between tires and sponges is to some extent a matter of surgeon preference their different physical properties favor their use in different situations depending on the number, size and location of retinal breaks. This can be illustrated by some examples:

Fig. 100.22 (A) Elevated tear closed by (B) radial sponge (nondrainage).

Fig. 100.23 (A) Atrophic round holes (varying distances from the ora) closed with (B) a broad tire.

Fig. 100.24 Extensive detachment in a pseudophakic eye with poor peripheral fundal view. The breaks are likely to be quite anterior. (B) An encircling tire has been used to close them.

Fig. 100.25 (A,B) Multiple tears closed with sponges.

Fig. 100.26 (A) Multiple tears closed with (B) a tire and gas bubble.

Fig. 100.27 Fishmouthing. The high indentation causes radial redundancy folds which keep breaks open.

Fig. 100.28 (A) Chronic dialysis closed by (B) an anterior circumferential 3-mm sponge.

Scleral sutures

Once the breaks have been marked, the size and position of the required buckle should be apparent so that partial-thickness scleral mattress sutures can be preplaced. Some surgeons prefer to carry out this step later in the operation following cryotherapy.

The desirable physical properties of scleral sutures are durability, biocompatibility and ease of handling. Monofilament nylon and polyester both possess all these properties. A braided surface modified polyester is slightly easier to handle than a monofilament suture: the friction between throws of the knot makes it easier to tie the knot under tension. Nylon however, has better “memory”, and several throws will keep the tension in the knot without resorting to slip knots or holding the knot between throws.

The suture bites are oriented parallel to the long axis of the explant (i.e., radial suture bites for a radial explant, circumferential bites for a circumferential explant).

The distance between the bites is significantly greater than the width of the explant. This allows the sclera to partially envelop the explant, creating the indent. For example, when suturing a 5-mm sponge, the bites are placed 8 mm apart. Silicone tires generally need a bite separation 2 mm greater than their width. Failure to space the bites sufficiently reduces the height of the indent. Calipers are used to ensure accurate bite separation (Fig. 100.29). The bites pass in opposite directions, so that the mattress suture has a box configuration and the sutures do not cross over on the buckle. Crossing over of the sutures reduces the length of the indent (Fig. 100.30). A box suture may be difficult to achieve with posterior radial bites, as it is easier and safer to pass a bite anteroposteriorly than it is to pass it posteroanteriorly. Use of a double-armed suture allows two anteroposterior passes of the needle. Alternatively, a figure-of-8 suture may be converted to a box suture by dividing the suture between the bites (Fig. 100.31).

Fig. 100.29 Calipers used to ensure the correct suture bite separation – in this case 8 mm for a 5-mm sponge.

Fig. 100.30 A crossed mattress suture (bottom) does not support the ends of the sponge as well as a box suture (top).

Fig. 100.31 Conversion of an (A) crossed mattress suture to (B) a box mattress suture.

Mattress sutures should have a square configuration, with the bites parallel to each other and the long axis of the buckle. Irregular nonparallel sutures cause less-effective indentation (Fig. 100.32).

Fig. 100.32 Irregular untidy sutures give uneven indents.

The sutures need to be placed partial thickness () through the sclera. As the scleral is only 1 mm thick, care needs to be taken to avoid scleral perforation. A spatulated needle rather than a cutting needle is used. The spatulated needle profile has a flat top and bottom and cutting lateral edges (Fig. 100.33). The sclera has a pseudolamellar structure.³⁹ When appropriately used, a spatulated needle tends to glide between the scleral lamellae.

Fig. 100.33 The structure of a spatulated needle. The side cutting tip favors its passage at a constant depth between scleral lamellae. This is a circle needle – a circle may be needed when access is difficult (e.g., posterior scleral sutures).

When suturing (and whenever putting needles in the globe, e.g. during drainage) a forceps held in the nondominant hand is used to grasp a rectus insertion. This positions and fixates the globe for the suture and also allows the intraocular pressure to be adjusted if the eye is very soft. The spatulated needle is mounted of the distance from its tip in a curved (e.g., Barraquer) needle holder.

The tip of the needle is placed on the sclera, so that the tangent of the tip is parallel with the surface of the eye. It is important to ensure the needle does not bank, as this may cause the needle to cut out laterally (Fig. 100.34). When placing posterior sutures, this is easiest to achieve while sitting on the opposite side of the eye from the surgical area (Fig. 100.35). In fact it is a good principle to always operate “over the cornea,” as this gives better access to the recesses of the sub-Tenon’s space.

Fig. 100.34 A spatulated flat should be laid flat on the sclera (A) – if it banks (B), it may cut out.

Fig. 100.35 Operate from the other side (“over the cornea”) for access to the posterior sub-Tenon’s space.

Gentle downward pressure creates a small indent (Fig. 100.36). The needle is now advanced, keeping the tangent of its tip parallel to the surface of the eye. This causes it to advance progressively deeper in to the sclera. Once it has reached the desired depth no more downward pressure is applied. The spatulated design of the needle allows it to glide (or delaminate) between the scleral lamellae at a constant depth.

Fig. 100.36 Safe passage of scleral sutures. The depth of the needle is gauged by its visibility throughout.

The depth of the needle passage is monitored continuously during its passage through the sclera. At a depth of 500 µm, the needle is only just visible. The depth of the needle can be varied during the pass. Downward pressure while advancing the needle will take it deeper into the sclera and slight rotation (or lifting) of the needle can be used to reduce its depth. While care must be taken not to perforate the sclera, the entrance and exit from the sclera should not be too shallow (Fig. 100.37). If the start or end of the bite is very superficial the sutures may partially tear out under tension. Once the bite is deemed of adequate length (usually 4–5 mm) the needle is rotated to bring the tip out of the sclera.

Fig. 100.37 Suture track. If the entry or exit is too shallow, the suture may cut out.

Great care must be taken with the heel of the needle at this stage to prevent it penetrating the sclera. A good rule is to focus one’s attention on the heel rather than the tip once the tip is clear of the sclera.

With experience, it is possible to modify this technique by initially engaging the scleral fibers more vertically with the tip before flattening the tip, indenting and advancing the needle.

The consequences of deep sutures depend on the state of the underlying retina. If the perforation occurs at a site with deep subretinal fluid the retina is generally unaffected and unless there is significant hemorrhage, there are no adverse consequences. If a deep suture is passed in an area of attached retina, a retinotomy may be created which will require retinopexy. In any event, the suture can act as a conduit for microorganisms to enter the eye and should be replaced. Deep sutures anterior to the spiral of Tillaux (as used for circumferential explants) do not injure the retina.

Tying the sutures

The aspiring vitreoretinal surgeon should have a good understanding of basic surgical principles. The properties of surgeons’ knots (Fig. 100.38A) and slip knots (Fig. 100.38B) are particularly important.⁴⁰ Scleral mattress sutures have to be tied under tension to create an indent. There are a number of ways of doing this.

Fig. 100.38 Surgical knots. The ends have been colored differently to highlight the knot architecture. A surgeon’s knot (A) is a square (or reef) knot with an extra forward throw. It is secure and compact but will slacken between the forward and backward throws unless the tension in the forward throws is maintained by grasping them with a second instrument. Alternately, multiple forward throws will maintain their tension. The tension in the knot cannot be easily adjusted unlike a slip knot (B), which can be easily tightened if using a low friction material. Note that the knot is inherently less stable unless extra turns of the suture are then added.

A slip knot (1–1–1) can be tightened on the second throw. In this case, two single throws are made without the special care needed to produce a surgeon’s knot. A slip knot generally occurs by default. One easy way of ensuring this is to do a single “forward throw” first and then a single “reverse” or “backward” throw but to pull the suture ends in the same direction on both throws (i.e., not to alternate the direction of pull as one would with a surgeon’s knot). Knot slippage requires low suture friction and is easier to achieve with synthetic monofilament sutures such as nylon and virtually impossible with Ethibond. Slip knots require extra throws after the tension has been adjusted to prevent later slippage and loosening of the knot.

A “locking” knot, where the two ends of the sutures are pulled firmly to one end between throws, maintains its tension after the first throw (although a double or even treble first throw is required). This can be achieved using any suture material.

A surgeon’s knot (similar to a reef knot but with a 2–1 structure) can be used if the assistant holds the knot with a pair of forceps between the first and second throws to maintain the tension of the first throw. The resulting knot is very compact.

Alternatively, one can rely on the friction and “memory” of a large number of throws to maintain the tension between the second and third throws. The resulting knot is bulkier than a surgeon’s knot.

The use of releasable bow knots allows subsequent retying to adjust the height of the buckle. The bow can finally be converted to a surgeon’s knot by cutting the loop and pulling on the shorter end of the cut suture through the knot.

Prominent suture ends may erode through the conjunctiva and ultimately lead to extrusion of the buckle. Once the knots have been tied securely the sutures should therefore be rotated bimanually to leave the knot lying posteriorly (Fig. 100.39). If nylon is used the ends should be trimmed close to the knot.

Fig. 100.39 Bimanual suture rotation to leave knots lying posteriorly.

Subretinal fluid drainage

Technique of drainage

Timing

Subretinal fluid may be carried out at various stages in the operation. The “DACE” (Drain air cryotherapy explant) sequence was developed for bullous retinal detachments. Subretinal fluid drainage followed by air injection to reform the globe prevents parallax errors during break localization. It has also been argued that cryotherapy may cause vascular congestion of the choriocapillaris and that subretinal fluid drainage should not therefore follow cryotherapy.⁴⁴ In practice, subretinal fluid drainage does not appear any more hazardous when performed after cryotherapy.⁴⁵ It can even be performed at the end of the operation.⁴⁶

Location of drain sites

The long ciliary neurovascular complexes run at 3 and 9 o’clock, and these sites should be avoided, as should the area around the vortex veins. Sites adjacent to (but not under) the horizontal recti are optimal from the perspective of avoiding choroidal vasculature.⁴⁴

Draining anteriorly may carry a lower rate of hemorrhage but drainage may be less complete than if the drainage is carried out more posteriorly. Drainage near the equator is usually a reasonable compromise. One advantage of draining “in the bed of the buckle” is that any retinal incarceration or break will be supported once the buckle is tightened. The planned drain site should be examined by indirect ophthalmoscopy immediately before drainage is carried out to ensure that the subretinal fluid is deep enough. Drainage where the subretinal fluid is very shallow risks not just incomplete drainage but retinal injury.

Drainage techniques

There are a number of different ways of draining subretinal fluid. Each relies on different strategies to avoid complications such as choroidal hemorrhage and retinal incarceration. The techniques can be classified as either two-stage techniques in which a large (cut down) sclerostomy with separate choroidotomy is made or those in which a very small sclerostomy and choroidotomy are made together.

Cut down techniques

A scleral incision 3 mm in length is made in the sclera, repeatedly spreading the edges, then incising the base of the resulting groove (Fig. 100.40, available online). The choroid becomes increasingly visible in the base of the incision. Finally a small knuckle of bare choroid protrudes slightly.

Fig. 100.40 Sclerostomy for a cut-down drain. Note location in the posterior bed of the buckle.

The choroidotomy can be made with a needle. Transillumination may be used to visualize and avoid larger choroidal vessels but there is still a risk of hemorrhage from the choriocapillaris.

Thermal choroidotomy may be used to reduce the risk of bleeding with this technique. A diathermy needle may be used to coagulate the choroidal vessels⁴⁷ and a diathermy needle used to perforate the choroid.⁴⁸ Alternatively, photocoagulation may be used. The tip of is laser endoprobe is positioned very close to the knuckle of choroid (Fig. 100.41). The laser is activated for 1–2 seconds at very high power (600 mW) until subretinal fluid is seen welling forward. The high beam divergence makes unintentional retinotomy unlikely and this technique has been used successfully in the presence of quite shallow subretinal fluid.⁴⁹ Use of an indirect laser for this step avoids the expense of an endolaser probe.⁵⁰

Fig. 100.41 Thermal choroidotomy using a laser endoprobe.

Single-stage techniques

Charles has described a technique using a 25-gauge hypodermic needle attached to an open syringe under ophthalmoscopic visualization (Fig. 100.42). The needle enters the globe anteriorly and is passed under the buckle and obliquely posteriorly in the subretinal space.⁵¹ Retinal incarceration is extremely unlikely and any retinal breaks created will be in the bed of the buckle and therefore supported. An increased risk of intraocular bleeding has been reported however.⁵² This may be averted by increasing the intraocular pressure to close the choroidal vascular bed, for example, by tightening an encircling band prior to drainage.⁴⁶

Fig. 100.42 Hypodermic needle drain. Note the bevel faces away from the retina. Suture needle drain. Note firm pressure on the globe to close the choroidal vasculature.

Suture needle drains use a spatulated needle held in a locking needle holder with 2.5 mm of the tip protruding (limiting the depth of penetration) (Fig. 100.43, available online).⁵³ Very firm pressure on the globe with a forceps at a rectus insertion elevates the intraocular pressure, closing the choriocapillaris before and for 5 minutes after the drain. A single rapid and decisive stab is made into the sclera and the needle immediately withdrawn.

Fig. 100.43 Suture needle drain. Note firm pressure on the globe to close the choroidal vasculature.

It is also possible to penetrate the sclera and choroid together using a specially designed diathermy needle which cauterizes to reduce the risk of hemorrhage.⁵⁴

Comparison of techniques

While performing cut down drainage, intraocular pressure elevation is avoided to prevent retinal incarceration. In needle drainage on the other hand there is no risk of incarceration (because the choroidotomy is so small) and a high intraocular pressure is desirable to reduce the risk of bleeding. When operating on bullous detachments, very rapid release of fluid can make it difficult to maintain a sufficient intraocular pressure and this may account for the increased risk of subretinal hemorrhage with this technique.⁵⁵

After drainage

Whichever drainage technique is used, it is prudent to be prepared for postoperative hypotony. Prolonged hypotony is dangerous during buckling surgery. It may lead to suprachoroidal effusions and hemorrhage,⁵⁶ hyphema, and pupil constriction. The scleral sutures should therefore have been pre-placed ready for tying and a syringe of air or saline with a small-bore needle at hand to reform the globe.

If subretinal fluid does not flow, or stops earlier than anticipated, the drain site is inspected to exclude a retinal incarceration and reassess the depth of subretinal fluid at the drain site. Star-shaped folds radiating from the drain site indicate a retinal incarceration (Fig. 100.44). It is not generally possible to re-posit the incarcerated retina in the eye and dangerous to try. The site of the incarceration is supported by an explant to relieve traction at this site, combined with retinopexy if there is also a retinal break.

Fig. 100.44 Retinal incarceration.

If there is deep subretinal fluid at the drain site gentle massage of the globe or distracting the sclerostomy edges may re-establish flow, otherwise a fresh choroidotomy may be needed.

The major complication of subretinal fluid drainage is choroidal hemorrhage. Subretinal blood tends to gravitate to the most dependent area of subretinal fluid – the macula if this is detached. The rate at which this occurs is probably contingent on the viscosity of the subretinal fluid (and therefore the chronicity of the detachment). It can have serious consequences for visual recovery, so steps should be taken first to limit bleeding and second, to displace the hemorrhage. First the intraocular pressure is elevated, either by tightening sutures or intravitreal injection (cut down drains should be closed with the prepared sutures if this is done). The patient’s head may also be tilted towards the drain site. Subfoveal hemorrhage may be displaced pneumatically⁵⁷ or removed subsequently by vitrectomy.⁵⁸

Air injection

When only small holes are present a soft globe may be reformed with saline but in the presence of large tears the fluid quickly leaves the eye and the eye will re-soften. The surface tension of a gas bubble prevents its passage through breaks. An additional advantage of air and gas injections is their ability to supplement the external buckling effect with internal tamponade of breaks. The major disadvantage of using air or gas is that they may make fundal view difficult particularly if the injection technique is poor. The gas injection technique is described in detail in Chapter 103, Pneumatic retinopexy, but there are some special considerations relating to the use of gases in buckling surgery.

Use of air or gas to reform a collapsed globe entails injecting into a soft eye. A number of modifications to the basic pneumatic retinopexy technique can make this easier. Use of an air pump can be particularly helpful for the less-experienced surgeon (Fig. 100.45). A 23-gauge needle is attached to the air line and the pump pressure set at a physiological level (i.e., 20 mmHg) before being clamped. The needle is introduced into the eye taking the precautions described in Chapter 103, Pneumatic retinopexy. The clamp on the air line is released and air rapidly enters the vitreous cavity until the preset pressure on the pump is reached. The rate of air flow is optimal and the final pressure physiological. This technique is relatively forgiving of errors in placement of the needle (and fish eggs are virtually never encountered).

Fig. 100.45 Air injection with an air pump. Note the single bubble despite suboptimal position.

Macular folds are a rare complication of the combination of subretinal fluid, air injection, and buckling (Fig. 100.46).^59,60 There is some uncertainty about the best way to avoid this devastating complication. Face-down posturing immediately after surgery to displace subretinal fluid away from the macula may be helpful.

Fig. 100.46 Compression fold following drain, air, and explant. This may be avoided by prone posturing.

Pneumatic retinopexy using expansile gas may be used to treat fishmouthing or to facilitate the closure of breaks that are significantly elevated after buckling.

If general anesthesia is used nitrous oxide should be discontinued at least 15 minutes before the injection to prevent unpredictable expansion of the bubble.⁶¹ Avoiding the use of nitrous oxide altogether removes this risk.

Encirclement

Segmental buckles provide local support which often fades. This may lead to reopening of breaks if insufficient retinopexy has been applied.²² Encirclement produces permanent support of the vitreous base retina. Indeed, encirclement has been used without any retinopexy⁶²: as the breaks are permanently supported there is no need to seal them.

The indications and evidence for encirclement are reviewed more extensively in Chapter 105, Optimal procedures for retinal detachment repair. There is little evidence to support the routine use of encirclement in buckling surgery and the procedure appears to have a significantly greater risk of complications than a segmental buckle. In practice, a case-by-case judgment has to be made on whether the benefits (the increased chance of success is probably quite modest) justify the risks.

Encirclement has a particular role in certain situations:

• Early PVR

• Very extensive scleromalacia

• Extensive detachment in which breaks are difficult to detect (for example in some pseudophakic eyes with small anterior breaks and capsular phimosis).

• Multiple breaks in three or more quadrants.

Encirclement is produced with a combination of a local silicone tire (confined to the areas of visible the breaks) with a 2-mm band, which lies in the gutter of the tire and encircles the globe before being attached to itself (Fig. 100.47). The 2-mm band is often too narrow to support breaks and its primary purpose is to maintain the height of the indent from the tire.

Fig. 100.47 The basic elements of an encirclement: a tire, a band, and a silicone sleeve.

The steps are:

1. A 360° peritomy with slinging of all four rectus muscles.

2. Break localization, retinopexy and pre-placement of the mattress sutures of the tire. Generally two sutures are required per quadrant.

3. Threading the tire and band together under the recti and mattress sutures. Ensure that both limbs of all the mattress sutures are above the buckle as it is not uncommon to leave one under the encirclement by mistake. Some thought needs to be given to where the ends of the band will be secured at this stage. It is also important to ensure that the band does not become twisted. An oblique trimming of the ends allows the orientation to be checked after the band has been passed around the globe (as a 180° twist will be immediately apparent).

4. Subretinal fluid drainage is required in the majority of cases. The exact stage at which it is performed is variable but it may be done now to create space for the indent.

5. Tighten the mattress sutures over the tire to create a local indent.

6. Place a small holding stitch over the band in each quadrant where there is no tire to stop it bow stringing forward when tightened. These are placed at the equator (approximately 12 mm behind the limbus).

7. Fasten the ends of the band to each other. A Watzke sleeve is a small silastic tube designed to secure the ends and allow adjustment of the tension in the band. The steps for engaging the ends of the band in the sleeve with a specially designed cross acting (“Watzke”) forceps are illustrated (Fig. 100.48).

8. The ends of the band are pulled to create the encircling indent. A 6-mm shortening will produce approximately a 1-mm indent, irrespective of the size of the globe. The end point of this tightening is best judged ophthalmoscopically; a shallow indent should be just visible. The practice of tightening the band to reform the eye after drainage is dangerous as it may produce a grossly excessive indentation.

9. The optic nerve perfusion should be checked and, if necessary steps taken to normalize it such as paracentesis, subretinal fluid drainage, or adjusting the buckle.

Fig. 100.48 Engaging (A–D) and (E) tightening the band, using a Watzke sleeve and forceps.

Recurrent retinal detachment

Persistent subretinal fluid is often seen in the early postoperative period, particularly if a nondrainage operation has been performed. Resorption of fluid may take much longer (Fig. 100.52), particularly in chronic detachments with subretinal precipitates and demarcation lines.⁷¹ Persistence of subretinal fluid alone is not an indication for revision surgery. Indications for early revision surgery are a visible open retinal break or increasing subretinal fluid.⁷²

Fig. 100.52 Rarely resorption of subretinal fluid (arrow) can take months.

Recurrent detachment is often due to errors in the initial surgery.⁹ Successful revision surgery starts with an analysis of the cause of failure. Is there an open break? Are the indents in the right place? Are they high enough to close the breaks? These questions are answered by carefully observing the distribution of subretinal fluid, the presence of subretinal fluid on indents and visibly open or unsupported breaks.⁹

Fig. 100.53 Failed buckle with subretinal fluid on the buckle inferiorly. (A) The indent is high in places but not over the break at 6 o’clock. Magnified view reveals open break (B, arrow). At reoperation (C) there is very little indentation inferiorly due to poor placement of the mattress sutures.

Fig. 100.54 Failed retinal detachment due to a missed dialysis. Lincoff’s rules indicate an undetected superonasal break.

Fig. 100.55 Recurrent retina detachment following encirclement (A). There is no fluid on the buckle. (B) Magnified view showing a break (arrow) posterior to the encirclement.

Fig. 100.56 The case in Figure 100.55 managed by local augmentation of the buckle using a sponge.

Fig. 100.57 Fishmouthing. Folds on the tire (A) with fishmouthing of the break (arrow) apparent in magnified view (B). This was managed successfully by pneumatic retinopexy (C).

Fig. 100.58 Misplaced sponge. The break is on the edge of the sponge (A), which has to be repositioned to close the break (B). Positioning of the apex of the indent under the tear is critical when using radial sponges.

Proliferative vitreoretinopathy, the most important cause of ultimate failure to reattach the retina, is discussed in Chapter 107, Proliferative vitreoretinopathy.

Glaucoma

Retinal detachment is associated with glaucoma,⁷⁵ so in some cases postoperative glaucoma may have been present preoperatively.

A steroid response is the commonest cause of open angle glaucoma after buckling surgery. Most cases of buckle-related angle closure glaucoma occur without pupil block.⁷⁶ The central anterior chamber is shallow due to forward displacement of the ciliary body (Fig. 100.59). This may be due to the combined effects of interrupted choroidal venous drainage and the mass effect of a large explant. This condition does not respond to iridotomy or miosis (which tends to exacerbate it). Most cases resolve after 1 week with conservative measures including steroids, cycloplegia, and ocular hypotensive agents. In intractable cases, the Watzke sleeve may need to be loosened or the band divided.

Fig. 100.59 Angle closure without pupil block after buckle. The high encirclement (A) causes choroidal venous congestion which displaces the ciliary body, and thus the whole lens–iris diaphragm, forward. (B) A slit-lamp photograph shows central and peripheral anterior chamber shallowing (in pupil block the central anterior chamber is deeper).

Epiretinal membranes

Epiretinal membranes at the macula are the commonest cause of visual loss after successful scleral buckling.^77–79 Their management is discussed in Chapter 116, Macular epiretinal membranes.

Extrusion/infection

These typically present several weeks or months postoperatively as an inflamed eye with purulent discharge. Even if exposure of the buckle is not evident, it is often possible to express some pus through associated conjunctival dehiscence. As infection and extrusion are often associated, it can be difficult to establish which comes first. The risk seems to be heavily influenced by the surgical technique used, radial sponges having a greater risk than circumferential ones.⁶⁵ This fact, together with the delayed presentation, suggests that in most cases microorganisms gain access to the explants though conjunctival dehiscences over protruding segment of buckle or suture rather than being introduced at the time of surgery. This highlights the importance of trimming the ends of sutures and explants and covering them well during closure. Closure of Tenon’s capsule and conjunctiva in separate layers may be the best way of achieving this, especially if the conjunctiva is particularly thin.

Bacteria produce a biofilm coating on explants which makes it impossible to eradicate them medically.⁸⁰ The only definitive treatment is removal of the explant.⁸¹ Provided adequate retinopexy has been performed recurrent retinal detachment is unusual.^82,83 If there is any doubt about this supplementary retinopexy may be carried out around the breaks before removing the buckle.

Removal of extruding radial sponges is generally easy and can often be done on the slit lamp. Encircling elements are technically more challenging and may require general anesthesia. Occasionally exposed encircling elements with minimal symptoms can be managed conservatively, particularly if the patient is in poor general health or the initial surgery was complex or complicated.

Buckle exposure tends to follow a relatively chronic course but occasionally patients develop acute sight-threatening complications such as endophthalmitis or scleritis^84,85 requiring urgent removal of all foreign material (explants and sutures) and local and systemic antibiotics.

Band migration

Encircling bands may intrude or migrate over the surface of the eye, usually anteriorly.

Intrusion is often an incidental finding but may cause vitreous hemorrhage or, less frequently, recurrent detachment many years after buckling surgery. It is usually managed conservatively. Vitreous hemorrhage and retinal detachment may both be managed by vitrectomy without disturbing the band.

Migration anteriorly may affect rectus muscle function and even cause the band to migrate anteriorly and extrude through the limbal conjunctiva.

Diplopia

Diplopia is common after scleral buckling surgery.⁸⁶ It tends to improve with time and intervention is only indicated for persisting diplopia which does not respond to prisms. Removal of the explant alone may cure the problem.⁸⁷ Strabismus surgery can be challenging due to the presence of buckles and adhesions. In patients with very extensive buckles which cannot safely be removed repeated injections of botulinum toxin may be useful.⁸⁸

Metamorphopsia following detachment of the macula may lead to poor sensory fusion with diplopia. It is important to identify these cases as the diplopia does not respond well to surgical intervention.

Anterior segment ischemia

Anterior segment ischemia is now rare, as very high encirclements and rectus disinsertion, both of which compromise the uveal circulation, are rarely used. Patients with sickle cell disease are at particularly high risk⁸⁹ and may benefit from exchange transfusion particularly if an encircling buckle has to be used. Presenting features are corneal edema, pain, anterior chamber flare, and a deep anterior chamber. The intraocular pressure may be high initially but falls as the ciliary body fails. Mild cases may be managed with topical steroids but severe cases carry a poor prognosis and loosening or division of the band should be considered.