October 2009

 

CATARACT/ IOL

 

Perspective in Lens & IOL Surgery

Endothelial dystrophy & cataracts


by Richard S. Hoffman, M.D.

 

It is a great honor and privilege to inherit the editorial responsibilities for the “Perspectives in Lens and IOL Surgery” column from I. Howard Fine, M.D. Howard has done a spectacular job of bringing us cutting edge articles on the latest and greatest technologies and techniques in modern lens surgery, incorporating both a practical and international perspective. Although no one can truly fill his shoes, I can only hope to continue his Fine work.

In this issue, we will discuss how recent improvements in posterior lamellar keratoplasty have changed our approach for treating patients with concomitant cataract and endothelial dystrophy. I believe you will find this article both informative and controversial.

Richard S. Hoffman, M.D. Column Editor

 

Advances in posterior lamellar keratoplasty changing our approach to cataract extraction in corneal endothelial dystrophy

DSAEK OCT

Guttata Source: Richard S. Hoffman, M.D.

Until recently, the treatment of patients with coexisting corneal endothelial dystrophy and cataract was somewhat straightforward. If corneal edema was not present and the cataract was visually significant, cataract surgery was undertaken with the utmost of care in order to prevent corneal decompensation and ultimately improve visual acuity by means of cataract extraction.

However, in patients with moderate endothelial dystrophy and borderline cataracts, the fear of inducing iatrogenic bullous keratopathy many times resulted in the postponement of cataract surgery in order for the cataract to become more advanced and more visually significant. This fear ultimately leads to a clinical situation where a cycle of postponement and continued endothelial cell loss through attrition makes corneal decompensation even more likely once cataract surgery can not be deferred any longer. This “damned-if-you-do” or “damned-if-you-don’t” scenario stems from the perception that causing corneal decompensation following phacoemulsification condemns a patient to all of the detrimental side effects of penetrating keratoplasty (PKP) including pain, induced myopia, significant astigmatism, prolonged visual recovery, and graft rejection. It is probably true that because of these disadvantages, PKP should be avoided at all costs if possible. The recent revolutionary advances in posterior lamellar keratoplasty have now completely changed the paradigm for approaching patients with coexisting cataract and endothelial dystrophy. Although earlier posterior lamellar procedures involved intricate dissections of the patient’s posterior cornea and complex hand dissections of the donor tissue, the technique has quickly evolved to the current simplified version of only stripping away the pathologic Descemet’s membrane and guttata and creating the lamellar donor tissue by means of automated microkeratome dissection. This DSAEK procedure (Descemet’s Stripping Automated Endothelial Keratoplasty) allows surgeons the capability of removing visually significant corneal guttata and replacing attenuated corneal endothelium with new higher cell counts and avoiding many of the downsides of penetrating keratoplasty. The procedure can be performed quickly through a 5 mm limbal incision with impressive 2 to 4 week visual recovery, no pain, little if any induced astigmatism, and none of the suture-related and full-thickness wound complications that could develop with full-thickness keratoplasty. DSAEK is to full-thickness keratoplasty as phacoemulsification was to intracapsular cataract surgery.

This revolution in keratoplasty has created many benefits and quandaries. Now when presented with a patient with coexisting endothelial dystrophy and cataract, the anterior segment surgeon can proceed with cataract surgery sooner, knowing that if corneal decompensation develops, the bullous keratopathy can be easily and quickly treated with DSAEK. In fact, the deleterious visual effect of moderate to severe corneal guttata many times makes iatrogenic corneal decompensation a blessing in disguise since the removal of these guttatae can be more visually significant than the removal of a moderate nuclear sclerotic cataract. On many occasions, I have performed a DSAEK procedure in one eye of a bilateral pseudophakic patient with bilateral moderate to severe corneal guttata and unilateral mild corneal edema. Following surgery in the 20/50 eye with mild corneal edema, patients have adamantly demanded DSAEK in their second 20/25 eye that had no edema and only guttata. Many of these second eyes didn’t even meet the current visual standards for undergoing cataract surgery but the presence of guttata was so visually deleterious in their second eye and the quality of vision so good in their first DSAEK eye that patients insisted on DSAEK to treat only their guttata. In patients with very mild corneal guttata, cataract surgery alone is indicated. However, when moderate to severe guttata (3–4+) is present, the approach to these patients is less clear. With more experience with the DSAEK procedure, I am finding myself more inclined to treat patients with visually significant guttata and cataract with a combined DSAEK/phaco/IOL procedure. When patients are referred from other anterior segment surgeons, I will have them perform the cataract extraction first and then assess patients’ satisfaction with the quality of vision and offer a DSAEK procedure if they require better acuity than what was provided by the cataract extraction alone. If corneal thickening was present pre-op or cell counts were borderline for corneal survival, then I will assume that DSAEK will need to be performed following the cataract extraction or I will perform a combined procedure from the start. One of the pleasantries of performing cataract extraction in a patient who you know will also be undergoing DSAEK is the ability to perform the phacoemulsification within the anterior chamber without consideration of preserving the central endothelium. Remember, it is going to be replaced anyway.

Currently, DSAEK will induce 1.0 to 1.5 D of hyperopia due to the negative meniscus shape of the lamellar lenticule that is implanted. Thus when planning combined DSAEK/phaco/IOL or staged phaco/IOL followed by DSAEK (at any time in the future), it is advisable to calculate the implanted IOL power to yield 1.0 to 1.5 D of myopia assuming an ultimate desire for emmetropia. Current work by Gerrit Melles, M.D., on a refinement of his DSEK procedure wherein the donor tissue contains only Descemet’s membrane and endothelium (DMEK – Descemet’s Membrane Endothelial Keratoplasty) rather than 100 microns of posterior corneal stroma, Descemet’s membrane, and endothelium (DSAEK) will ultimately result in even faster visual recovery and no hyperopic shift since the negative meniscus donor shape will be eliminated. This new procedure is still undergoing refinement and has not yet been widely employed.

The DSAEK procedure currently utilizes a 5 mm wound in order to minimize endothelial cell loss in the donor graft. There are several companies working on devices and injector systems that will hopefully implant these grafts atraumatically through 3 mm incisions. This will allow for the combined DSAEK/ phaco/IOL procedure to be performed through a 3 mm temporal clear corneal incision without the need to widen the incision to 5 mm for graft implantation.

The rapid advances in posterior lamellar keratoplasty have allowed us to approach our patients with concomitant cataract and endothelial dystrophy in a new light, but have also added new controversy to the treatment of these patients. Should we be treating moderate to severe corneal endothelial dystrophy without corneal edema with DSAEK? Do we have enough corneal tissue to treat all of these patients? How long will these grafts last? Are Snellen acuity and glare testing alone an acceptable means of measuring the visually debilitative effect of guttata? What level of detriment is considered acceptable for proceeding with DSAEK combined with cataract extraction? I believe just as our indications for proceeding with cataract surgery have relaxed due to better results from improvements in phacoemulsification technology and technique, so too will our indications for treating corneal endothelial dystrophy in the presence of cataract. Time will tell.

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