Primary Pre-Descemetic DALK in Acute Corneal Hydrops and Non–Big Bubble DALK in Older Patients

Soosan Jacob, MS, FRCS, DNB, MNAMS, and Areeckal Incy Saijimol, BSc

PRIMARY PRE-DESCEMETIC DALK IN ACUTE CORNEAL HYDROPS

Acute corneal hydrops results from a spontaneous tear in the Descemet’s membrane (DM) occurring in patients with advanced keratoconus. Aqueous seepage into the stroma through the tear results in a symptomatic patient with sudden decrease in vision. Conventional treatment for acute hydrops was medical management and, more recently, has consisted of intracameral gas (air, C₃F₈, SF₆, or C₂F₆). Though the acute hydrops generally resolves with these measures, it heals with the formation of a scar. The flattening caused by this scar formation can result in improvement in contact lens tolerance. Scarring may also result in improvement in visual acuity with peripherally located scars, albeit with disadvantages of the need for special and expensive contact lenses, limited hours of contact lens wear, poor vision in non–contact lens hours, poor contact lens fit and consequent complications, such as apical touch, apical scarring, and infectious keratitis. However, because it is often difficult to predict the location where scarring will develop or its extent, conventional treatment carries the risk of a scar developing in the visual axis that can impair vision. Many of these patients, therefore, ultimately require a secondary procedure either in the form of a pre-Descemetic deep anterior lamellar keratoplasty (PD-DALK) for peripheral scarring or a penetrating graft for centrally located scars.1–14 The author (SJ) has described her technique of modified primary PD-DALK in acute corneal hydrops in a series of cases as immediate primary management modality at the time of presentation^15,16 to avoid post-hydrops scarring while providing visual, optical, topographic, structural, and biomechanical improvement while decreasing, and often avoiding, contact lens dependence as well as avoiding scar formation.

Clinical Examination and Investigations

Slit lamp examination of an eye with acute hydrops shows epithelial microcystic edema, stromal edema and swelling, intrastromal cyst/clefts, and conjunctival hyperemia. Careful examination may reveal the margins of the tear in some cases. Vision and intraocular pressure should be checked. Anterior segment optical coherence tomography (ASOCT) may be used to determine the corneal pachymetry, the extent of the tear along both the longest and shortest dimensions and location of the tear, as well as the amount of stroma over the tear. Topography of the involved eye may not be possible, but topography of the other eye may show evidence of keratoconus. In the absence of the ability to see the fundus clearly, an ultrasound evaluation of the posterior segment should be done.

Technique

The important surgical considerations to be understood for attaining a successful outcome are the following:

• The Descemet’s tear is a weak point and should not be stressed mechanically.
  
• Thin layers of pre-Descemetic tissue should be retained over the tear in order to avoid opening the anterior chamber.
  
• In certain eyes with extensive thinning and hydrops, there may be very thin residual stroma over the break. In these cases, pressure from trephination of the cornea should be avoided.

Peribulbar block is used for cooperative patients. Intravenous sedation may be given. The desired diameter of the host bed is estimated by caliper. Depending on the structural integrity of the cornea, a decision is made as to whether a partial-thickness trephination of the cornea is possible. A partial-thickness trephination is performed in cases where the globe offers sufficient counter pressure. In cases with severe thinning and insufficient stroma over the tear, an inked trephine is instead used to mark the corneal surface. A sharp bevel up crescent dissector is then used to deepen this groove. A 26-gauge needle bent with its bevel up (instead of bevel down, as in big bubble DALK) is then mounted on a 1 mL syringe and used to inject air gently at multiple quadrants. The needle is inserted tangentially around the break at multiple spots and air is injected slowly in a graded manner in small aliquots around the tear, as well as other areas of the cornea, avoiding acute build-up of air pressure. The anterior stroma is then debulked with a blunt crescent blade using the emphysematous cornea as a guide to depth of dissection. An air bubble is then injected into the anterior chamber and deeper dissection is performed circumferentially from all sides starting from the periphery and working carefully towards the center using the Melles technique. The central undissected stroma is removed at the end dissecting carefully over the area of break. Minimal stroma is intentionally retained over the tear in order to retain a closed anterior chamber. If at any point the anterior chamber is soft or shallow, air is injected into the anterior chamber through the small paracentesis. Finally, a same-sized graft trephined from a donor corneoscleral rim from which DM has been removed, is sutured onto the host bed. Air is finally injected into the anterior chamber to tamponade the DM tear (Figures 9-1 and 9-2 and Video 9-1).

Discussion

In a case series of 11 patients presenting with acute hydrops, the author has successfully performed PD-DALK using the aforementioned modifications in all cases without any corneal perforations. Though air entered the anterior chamber through the DM tear in many cases, it did not enlarge the tear in any case in our series. All corneas healed without scarring over the area of the Descemetic tear, which is a major advantage (Figures 9-3 and 9-4). This is unlike the healing by scarring that is generally seen after conventional management techniques (Figure 9-5A). It can take up to 2 to 3 months for healing post-hydrops, and it is probable that this prolonged period of persistent edema provokes increased inflammation that results in healing by scarring. A secondary PD-DALK done for healed hydrops also often cannot attain complete scar removal and residual scar is common and can be a disadvantage when in the visual axis (Figure 9-5B). Intracameral gas keeps the torn Descemet’s edges widely separated under an ectatic cornea, whereas a primary DALK brings the torn edges closer with decreased separation. As the edema has a fast resolution following primary PD-DALK, none of the cases in our series showed scarring in the area of Descemet’s tear and the overlying stroma remained clear in all patients. Maintenance of clarity in the absence of endothelial cells in the area of tear is because of the ability of the adjacent endothelial cells to maintain corneal deturgescence. Endothelial cells may also enlarge and slide over to cover the defect, though confocal microscopy would be needed to prove this. This is similar to the stromal clarity that is maintained in the gap between the graft and the area of host Descemetic stripping following a DM-endothelial keratoplasty.

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