Complications After DALK

Claudia Perez-Straziota, MD and Ronald N. Gaster, MD, FACS

Anterior lamellar keratoplasty (ALK) has been proposed as an alternative for patients with corneal disease confined to the anterior aspect of the cornea. It offers the advantage of superior structural integrity compared to penetrating keratoplasty (PK), as well as the absence of endothelial graft rejection, as the host’s endothelium is preserved (Figure 11-1). With the introduction of deep anterior lamellar keratoplasty (DALK) and Anwar’s big bubble technique for stromal removal, ALK has regained popularity in the area of lamellar keratoplasty. Many of the complications after DALK are somewhat similar to PK; however, there are some complications specifically associated with DALK that will be discussed in this chapter. For the sake of simplicity, the complications have been divided into intra- and postoperative; however, many of the complications that have occurred from surgical technique manifest in the early postoperative period. Prompt diagnosis and management of these complications is of utmost importance to maximize the chance of graft survival.

INTRAOPERATIVE COMPLICATIONS

Descemet’s Perforation

Inadvertent perforation of Descemet’s membrane (DM) can occur during stromal dissection, especially in cases of incomplete big bubble formation that requires manual dissection of the stroma¹ (Figures 11-2 and 11-3). DM perforation occurs more frequently in patients with advanced keratoconus who have abnormally thin corneas, and has been reported to occur in 2% to 12% of cases with experienced surgeons.1–5 Fortunately, the postoperative prognosis when these perforations are successfully managed does not deviate from the expected prognosis in uncomplicated cases,^6–8 because most of the time the DALK procedure can proceed as planned. Hence the rate of intraoperative conversion to PK after small DM perforations has decreased significantly to 2% with the development of new surgical techniques for stromal removal.⁴

Depth-adjustable trephines will decrease the risk of perforation during trephination, when the peripheral corneal thickness can be measured prior to surgery (Figure 11-4). A conservative trephine cut to the level of the anterior two-thirds of the cornea is advised to avoid incurring the risk of DM perforation during trephination. Additionally, maintaining a somewhat shallow anterior chamber will not only minimize the risk of perforation but also minimize the size of the perforation should it occur, therefore making it more manageable and increasing the chances of being able to continue with DALK as planned. Perforations can also occur during suture placement; complete Descemet’s dissection beyond the area to be grafted provides a peripheral stromal rim that has been dissected off DM and can be used as a holding point for the forceps, providing direct visualization of the stromal thickness to be sutured on the host’s side (Figure 11-5).

If a tear in DM is suspected, pressure in the anterior chamber should be lowered to the minimum in order to prevent further extension of the tear. Additionally, once a DM tear has been identified, the approach to dissection of the remaining stroma should be modified accordingly. In perforations less than 2-mm diameter and located peripherally, the extension of Descemet’s dissection can be reduced to the central 5- to 6-mm diameter, as this would still be sufficient for a good visual outcome. However, for larger tears that involve more than 2 or 3 clock hours, conversion to PK is advised in most cases.

Proceeding with DALK when there is a defect in DM should be considered in cases where DALK is going to provide a specific benefit compared to PK, such as highly vascularized corneas, patients with history of infectious keratitis or severe atopia, or patients with severe ocular surface disease. Management options for small tears or perforations include intracameral air injection for tamponade, direct suture of DM to donor stroma when the tear occurs during initial trephination, and in some reports, fibrin glue has been suggested as an alternative for peripheral perforations9 (Figure 11-6). The most widely use technique, however, is intracameral air tamponade, which will provide support to DM against the donor stroma while endothelial cell migration occurs to heal the tear. This is also proven by the Jacob technique of performing a PD-DALK as a primary procedure for acute hydrops^10,11 (Figure 11-7).

Intra-Descemet’s Membrane Air Bubble

DM is ultrastructurally conformed by 2 distinct layers: the anterior, banded zone, which averages 3 μm and varies very little throughout life, and the posterior, non-banded zone, which measures 3 μm for the first 20 years of life and increases thickness thereafter up to 10 to 20 μm at the age of 80. Histological studies of DM have demonstrated that these zones can be easily separated when tangential forces are applied to the anterior stroma.12,13 In histopathologic specimens evaluated after DALK, Hirano et al¹⁴ observed the attachment of a thin band of DM to the anterior stroma in several cases, proving that the dissection that can appear as to be separating DM from the posterior stroma may actually have occurred through DM separating the 2 distinct bands.

First described by Anwar¹⁵ and Touboul,¹⁶ an intra-Descemet’s air bubble can occur when air dissects through DM, separating the anterior and posterior bands. Despite its rare occurrence, cases in which corneal scarring or deep stromal corneal dystrophies, such as corneal macular dystrophy, have increased thickness of the posterior non-banded layer¹⁷ are at increased risk of intra-Descemet’s air bubbles.

In comparison with the big bubble, intra-Descemet’s air bubbles easily slide under the tip of a fine cannula and are smaller and well-circumscribed. Paracentral bubbles and peripheral bubbles should be displaced as peripherally as possible and very carefully perforated with attention to leave the underlying layer of DM intact. Central bubbles should first be attempted to be displaced peripherally, otherwise the big bubble must be ruptured along with the intra-Descemet’s bubble, also with extreme caution not to perforate the underlying DM. Viscoelastic should be injected into the created space prior to dissection of the remaining stroma in order to protect DM.17

Rarely, a PD-DALK may be done over an unrecognized Type 1 big bubble (Figure 11-8), which may then be noticed only in the postoperative period. This generally requires only observation as the big bubble spontaneously gets reabsorbed.

A Type 2 big bubble, if formed, is important to recognize, as these are flimsier and more liable to rupture (Figure 11-9).

Role of Intraoperative Optical Coherence Tomography

Intraoperative microscope-integrated optical coherence tomography can be of use in determining the extent of air penetration into the corneal stroma, depth of trephination,¹⁸ assessment and management of Descemet’s detachments,¹⁹ and assessment of iris apposition onto the host’s cornea or misdirection of air into the posterior chamber.^20–22 Nevertheless, randomized control studies and standardization of intraoperative protocols are necessary in order to incorporate this technology into the routine surgical procedure.

Folds in DM can be seen in early postoperative examinations (Figure 11-10). They occur more frequently in patients with advanced keratoconus,⁴ likely from donor-host size mismatch. When located in the visual axis, Descemet’s folds can induce glare symptoms or affect visual acuity, likely through inducing higher order aberrations. In contrast, when located peripherally, these folds are usually not visually significant.

Descemet’s baring only in the central 5 mm has been proposed as a strategy when performing DALK in patients with advanced keratoconus,²³ in order to leave a peripheral stromal rim that will provide better support to the graft and decrease the chance of postoperative Descemet’s folds.

Early postoperative epithelial defects are very common after keratoplasties in general. In reported studies, 93% of DALK procedures have an epithelial defect on postoperative day 1 that generally heal completely within 3 days. However, persistent epithelial defects, defined as a non-healing epithelial defects, lasting more than 7 days, can occur in 2% to 9% after DALK.24,25 The presence of early epithelial defects is correlated with longer donor preservation-to-surgery times, epithelial sloughing during donor preparation, and quality of the graft in regards to specular microscopy, presence and extent of corneal folds and stromal cloudiness.²⁴

Successful management of persistent epithelial defects is important, as they can predispose to the development of microbial keratitis. The placement of a therapeutic soft contact lens with appropriate antimicrobial prophylaxis, amniotic membrane, serum tears, or eventual tarsorrhaphy in recalcitrant cases are all suggested strategies for management. Maintaining topical antibiotic therapy during epithelial healing is of utmost importance to prevent microbial superinfection.

Descemet’s Detachment: The Double Anterior Chamber or Pseudo Anterior Chamber

Descemet’s detachments, which are usually caused by Descemet’s perforations during surgery,²⁶ occur more frequently when manual stromal dissection becomes necessary due to an incomplete big bubble formation.¹ The double anterior chamber can be easily recognized during early postoperative examinations, delineated by the donor’s stroma anteriorly and the host’s DM posteriorly. In cases where corneal transparency is compromised and the view to the anterior chamber is poor, visualization of a DM detachment can be challenging. The use of anterior segment optical coherence tomography (ASOCT) can aid visualization of these detachments as well as quantification of their extent (Figure 11-11).

Even though the majority of double anterior chambers are noted in the immediate or early postoperative period, there have also been reported cases of spontaneous Descemet’s detachments up to 4 weeks after DALK in patients with advanced keratoconus²⁶ who had an uneventful early postoperative course. Therefore, careful examination of the anterior chamber should be consistent throughout postoperative visits. A double anterior chamber can also occur due to retained viscoelastic in the donor-host interface, and this can be differentiated from cases due to inadvertent Descemet’s rupture by observing the mobility of DM, which is reduced in cases of retained viscoelastic, as well as the degree of corneal edema, which is less in cases of retained viscoelastic.

Although spontaneous resolution of the double anterior chamber has been reported,^3,27–30 these occur mostly in cases where the Descemet’s detachment is due to retained viscoelastic. Early intervention with high-frequency topical steroids in small detachments, or insertion of air into the anterior chamber in larger or complete detachments, provides faster visual rehabilitation and decreases the risk of fibrosis, which could make management more difficult. In cases where there is no response to early intervention, retained stroma or viscoelastic in the donor-host interface should be suspected, and the interface should be irrigated intraoperatively to remove the retained material.31 In recalcitrant cases of double anterior chamber where a Descemet’s tear had been documented intraoperatively, proceeding to PK as a reintervention is recommended.

Toxic Anterior Segment Syndrome

Despite being mainly an extraocular procedure, toxic anterior segment syndrome has been reported in a case of DALK,³² most likely due to intraocular penetration with the cannula through the side incision during the instillation of air and/or balanced salt solution into the anterior chamber (Figure 11-12).

Even though endophthalmitis usually presents after the first 24 to 48 hours, and inflammatory findings at this early postoperative period usually point to toxic anterior segment syndrome, there have been reported cases of early onset endophthalmitis, especially from Staphylococcus epidermidis and Bacillus cereus. Therefore, endophthalmitis should be ruled out prior to initiating treatment with high-dose topical steroids by obtaining aqueous samples for microbiology analysis.

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