Intraoperative and Postoperative Complications of Anterior Lamellar Keratoplasty

Key Concepts

Descemet membrane perforation is the most common intraoperative complication in deep anterior lamellar keratoplasty (DALK).
Management of anterior chamber pressure can help avoid irreversible damage to the Descemet membrane.
Double anterior chamber is a common postoperative complication in DALK.
Air tamponade is effective in treating double anterior chambers, but care is needed to avoid pupillary block.

Anterior lamellar keratoplasty can be divided into two distinct methods to replace the corneal stroma. Deep anterior lamellar keratoplasty (DALK) refers to the technique that replaces most of the host stroma down to the Descemet membrane (DM). With the introduction of techniques such as the big bubble or the viscodissection technique, more surgeons now perform DALK as first choice of surgery for stromal disease. The term “anterior lamellar keratoplasty (ALK)” technically includes the DALK technique but is now often used to refer to the classical lamellar technique that preserves deeper layers of the host stroma. However, drawing a line between ALK and DALK can be difficult. Strands of stromal fibers, or a thin layer of pre-Descemetic stromal tissue, may remain following some of the techniques reported in the literature. The significance of completely exposing DM during DALK in terms of optical clarity and visual function remains to be determined. For the sake of simplicity, the term DALK in this chapter will include both complete DALK and pre-Descemetic DALK. Similarly, ALK will refer to techniques that intentionally preserve posterior layers of host stroma.

Indications for Anterior Lamellar Keratoplasty

Indications for anterior lamellar surgery are discussed in detail in Chapter 118 . However, avoiding possible complications encountered during ALK and DALK begins by choosing the right patient for surgery. ALK is a much safer surgery compared to DALK, since the risk of compromising DM is less. On the other hand, DALK recreates the normal physiologic anatomy of the cornea by avoiding intralamellar incisional planes in the stroma. This difference may be irrelevant in disease involving the anterior stroma such as Avellino dystrophy or scars. However, in vascularized corneas following infections or ocular surface disease, the weak adhesion between donor and host stroma allows for the invasion of vessels and subsequent deposition of lipids that will eventually hinder vision. DALK also provides for visual quality comparable to penetrating keratoplasty, while vision following ALK may be compromised by interface haze.

The decision to perform DALK must be made by weighing the risk/benefit ratio for the patient as well as the experience level of the surgeon. Patients at low risk for DALK include those that might do well with PK such as elderly dystrophy patients and keratoconus patients. Several options described later in this chapter are available when DM is ruptured during DALK, the easiest being conversion to PK. While patients will benefit from the reduced risk of immunologic rejection with DALK, converting to PK is an acceptable risk in patients with diseases that have fared well with PK in the past. On the other hand, patients with vascularized corneas have a high-risk of immunologic rejection of the endothelium following PK and performing DALK successfully is imperative. This subset of patients includes those with herpetic keratitis, infectious keratitis, severe atopic keratitis, and ocular surface disease with simultaneous limbal transplantation. Since these patients will benefit most from DALK, attempting DALK is certainly worth the effort.

Surgical Instruments to Prevent Intraoperative Complications

Most facilities equipped with instruments for PK should be able to offer DALK to their patients. In addition to the standard instrumentation, the following devices can be considered to reduce surgical complications.

Pachymeter: pachymetry is used during surgery to measure corneal thickness in patients with irregular corneas. It can be particularly useful in keratoconus patients prior to trephination of the cornea.
Slit lamp attachment to surgical microscope: This device is used to determine the thickness of the residual stroma and to confirm attachment of DM at the end of surgery. If there is a double anterior chamber (DM detachment) at the end of surgery, the slit beam can be used to confirm the effects of an air bubble injected into the anterior chamber. Residual viscomaterial between the host and graft can also be detected and avoided by slit lamp examination.
Blunt-tipped scissors and spatula are used to excise stromal tissue above DM. Scissors with sharp tips may inadvertently perforate DM during manipulation. Blunt-tipped, broad spatulas are handy when dissociating stromal fibers above the DM.
Intraoperative OCT is a powerful tool to observe the three-dimensional structure of the cornea during surgery. It can also be used to detect a DM detachment at the end of surgery.

Intraoperative Complications

Perforations and Ruptures of Descemet Membrane

The most common complication encountered during DALK is perforation of DM during surgery, which occurs in approximately 10% –30% of attempted cases. Patients with a high-risk of DM perforation include young keratoconus, while the risk is less in elderly patients who tend to have a thicker DM due to the increase in secondary DM fibers. DM perforation can occur in different surgical steps, and concentration during these crucial moments can greatly reduce the risk of rupturing the DM. DALK procedures using air (“big bubble”) or visco-bubbles can cleave the DM in two different planes. A pre-Descemet layer can remain on the DM (Type 1 bubble), or the bubble may form between the pre-Descemet layer and the DM (type 2 bubble). Rupture of the DM is more common in type 2 bubbles.

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