All about corneas
Keeping an eye out for corneal disease

Keep your eye
out for these
corneal problems:

1) Anterior basement membrane dystrophy; Pterygium Neurotrophic keratopathy (i.e., from previous herpetic keratitis); Ocular surface disease (i.e., dry eyes, ocular cicatricial pemphigoid, Stevens-Johnson syndrome)

2) Stromal Peripheral corneal thinning or ulcerative disorders from Terrien’s marginal degeneration and collagen vascular disease (i.e., rheu-matoid arthritis, systemic lupus erythematosis, Wegener’s granulomatosis, etc.); Ectatic disorders (i.e., keratoconus, pellucid marginal degeneration); Corneal scars Corneal dystrophies

3) Posterior Fuchs’ endothelial dystrophy, other various dystrophies (i.e., posterior polymorphous dystrophy or PPMD)

Source: Terry Kim, M.D.

Addressing severe corneal disease before cataract surgery crucial to optimum outcomes, say physicians

This patient has ABMD changes
in the epithelium, actually
lifting the epithelium up,
causing “negative staining”
on the blue, flourescein photo.
The slit photo shows that
the irregularities are in
the epithelium and not under
the LASIK flap that is not
epithelial ingrowth.
Source: Christopher
Rapuano, M.D.

While phacoemulsification is one of the most routine surgeries for ophthalmologists, severe corneal disease presents unique challenges that often must be dealt with first (or during combined surgery) to achieve superior outcomes.
That’s not to say patients who have anterior basement membrane dystrophy, irregular astigmatism, or a variety of other corneal problems can’t achieve good outcomes. But ophthalmologists must be informed of the latest conventional wisdom and use the right tools to detect these problems and address them as well as the cataract.
As a subject of substantial importance, assessing corneal disease before cataract surgery recently was presented by David B. Glasser, M.D., assistant professor of ophthalmology, Wilmer Eye Institute, Johns Hopkins, Baltimore, at Cornea Day 2006 in San Francisco.
“Even if this only occurs in 1% to 2% of patients, addressing it will help avoid post-op surprises,” Dr. Glasser said.
His colleagues couldn’t have agreed more.

What to look for

Before treating the cataract it is important to look for various signs of severe corneal problems, Dr. Glasser said. These include lid and ocular surface disease, epithelial disease, stromal opacity/thinning, endothelial disorders, and topographic abnormalities, Dr. Glasser said.
Terry Kim, M.D., associate professor of ophthalmology, Duke University Eye Center, Durham, N.C., divides the analysis of corneal disease into three groups to simplify things: looking for anterior, stromal, and posterior problems.
As far as the anterior portion of the cornea, it’s important to look for signs of severe anterior basement membrane dystrophy, pterygia that could cause corneal distortions, neurotrophic keratopathy (i.e., from previous herpetic keratitis) and ocular surface disease such as dry eyes, ocular cicatricial pemphigoid, or Stevens-Johnson syndrome. These conditions can affect pre-op keratometry measurements as well as vision and healing after cataract surgery.
Jonathan B. Rubenstein, M.D., professor, department of ophthalmology, Rush University Medical Center, Chicago, added that it is important to look for peripheral corneal thinning, which may be associated with rheumatoid-type diseases and can lead to surprises in terms of the structure and strength of peripheral corneal incisions, especially in cases of LRIs.
Pterygia should be considered on a case-by-case basis, depending on how extensive they are, Dr. Rubenstein said.
“Some are just cosmetic problems,” he said. “However, if they are visually significant, they should be excised before cataract surgery.”
In terms of stromal conditions that should be considered before cataract surgery, include aforementioned peripheral corneal thinning or ulcerative disorders due to Terrien’s marginal degeneration and collagen vascular disease (i.e., rheumatoid arthritis, systemic lupus erythematosis, Wegener’s granulomatosis, etc.), ectatic disorders (i.e., keratoconus, pellucid marginal degeneration), corneal scars, and corneal dystrophies, Dr. Kim said.
“Depending on the severity and location, a corneal scar could affect keratometry measurements as well as decisions regarding incision type and location” he said.
The posterior portion of the cornea also has the potential for many issues, primarily with Fuchs’ endothelial dystrophy.
“You need to know about Fuchs’ dystrophy before cataract surgery because the surgery can cause further injury to the remaining endothelial cells and lead to corneal edema,” Dr. Rubenstein said.
Physicians have to make a judgment call regarding whether or not to perform cataract surgery in a Fuchs’ dystrophy patient with early corneal edema.
The Ocular Hypertension Treatment Study (OHTS) has shown that people have a large range of corneal thicknesses and that even with 600-micron corneas patients can have normal endothelial function, Dr. Glasser said. Then again, when patients get into that range of thickness, it could be a result of a corneal problem such as Fuchs’ dystrophy, he said.
“Because a risk of corneal decompensation after cataract surgery increases with increased pre-op corneal thickness in patients with disease, in the past we recommended combined surgery with corneal transplantation in patients with a corneal thickness over 600 microns,” Dr. Glasser said.
As surgical techniques and instrumentation have improved, and with the introduction of ophthalmic viscosurgical devices, that threshold has increased to 640 microns.
“We now tend to do cataract surgery with lens implantation alone in patients with corneal thickness up to 640 microns,” Dr. Glasser said. “Again, there is some judgment involved because the risk is going to be higher in a patient in his 80s with dense nuclear sclerosis than in a patient in his 50s with a soft nucleus and posterior subcapsular cataract.”
During the 2005 ASCRS•ASOA Symposium & Congress in Washington, D.C., Gerami D. Seitzman, M.D., department of ophthalmology, Krieger Eye Institute, Sinai Hospital of Baltimore, and assistant professor of ophthalmology, Wilmer Eye Institute, Johns Hopkins, presented a study that found that in 12 Fuchs’ dystrophy eyes with a pre-op corneal thickness of > 640 microns the vast majority (10 eyes, 83%) did not require a corneal transplant within the first year after cataract surgery and had an average post-op BCVA of 20/50.
“Our data support the safety of careful cataract surgery in Fuchs’ dystrophy patients with pre-operative pachymetries greater than 600 microns,” Dr. Seitzman said. “To avoid cost and delay in visual rehabilitation we suggest that current recommendations to consider an initial triple procedure at pre-operative pachymetries greater than 600 microns be expanded. Pre-operative pachymetry greater than 640 microns may be a better guideline.”

A better analysis

While slitlamp and keratometry are indispensable tools to diagnose corneal problems, other tools often come into play as well, Dr. Glasser said. Pachymetry and topography may be used in selected cases.
“Using pachymetry to measure central corneal thickness allows a surgeon to estimate the risk of corneal decompensation after surgery,” Dr. Glasser said.
Meanwhile, the advantage of topography is, particularly in patients with asymmetric astigmatism, the ability to plan secondary interventions such as LRIs or the use of an excimer laser, Dr. Glasser said.
In fact, irregular astigmatism is best detected by corneal topography, Dr. Rubenstein said. Topography also is very helpful in detecting keratoconus, Dr. Rubenstein said, and Dr. Glasser said it’s a benefit in evaluating patients with stromal scars because there is a significant astigmatic component to those patients as well.
Specular microscopy may be used more infrequently, Dr. Glasser said. This diagnostic capability, which measures endothelial cell density, is useful but not as helpful as pachymetry in determining endothelial reserve, he said.
“But in advanced cases of cell loss this can be quite useful in demonstrating those changes, although most cases can be managed without the need to do this,” Dr. Glasser said.

Treatment options

While treatment options for severe corneal problems are vast, one key issue to consider is combined surgery.
For instance, if one does decide for a particular patient that the risk of corneal decompensation is high, then one has to decide whether or not to do transplantation followed by cataract surgery at later date or a combined procedure, Dr. Glasser said.
On one hand, combined surgery leads to more rapid visual recovery and can be accomplished with a single surgical procedure, but the surgeon cannot tell what the post-op keratometry will be, which presents a problem in determining lens power selection, he said.
On the other hand, corneal transplantation first can lead to much more accurate lens power calculation, but the course of visual rehabilitation is much longer, which is not something that all patients are prepared to accept, he said.
As far as anterior basement membrane dystrophy is concerned, Dr. Kim said epithelial debridement may be a treatment option as well as anterior stromal puncture if the disease is focal and not in the visual axis. If the disease is diffuse, PTK or epithelial debridement is a better option, he said.
Corneal scarring may be able to be resolved with PTK, but if not, corneal transplantation would be an option, Dr. Rubenstein said. Corneal dystrophies also may be addressed via PTK or corneal transplantation, Dr. Kim said.

Editors’ note: None of the physicians cited has any financial interests related to his comments.

Contact Information
Glasser: 443-283-8800, dbg@comcast.net
Kim: 919-681-3568, terry.kim@duke.edu
Rubenstein: 312-563-2305, Jonathan_Rubenstein@rush.edu
Seitzman: 410-601-5991, gseitzma@lifebridgehealth.org