Treat Corneal Irregularities Before Cataract Surgery
It is often said that what is diagnosed before surgery is the patient's problem and what is diagnosed after surgery is the surgeon's problem.
This is especially true when it comes to visually significant corneal surface irregularities. Patients with these irregularities who are referred to us after cataract surgery often complain of continued vision problems. This usually improves after treatment, but patients may not be very happy with their surgeon because of the additional office visits, unexpected treatments, and delay in obtaining good postoperative vision. Some may even feel the cataract surgery (or surgeon) actually caused the corneal surface irregularities.
Getting ahead of the problem is the ideal solution, as shown in a recent study of the common corneal surface irregularities epithelial basement membrane dystrophy (EBMD) and Salzmann nodular degeneration (SND). The authors clearly demonstrate that appropriate management of cataractous eyes, particularly patients with EBMD and SND, results in clinically significant changes in spherical and toric intraocular lens (IOL) power.
Why, Whom, and How to Treat
Better comfort, better high-contrast sensitivity (eg, Snellen chart) and quality of vision (less shadow vision, glare, or halos), and less fluctuation of vision are among the reasons to treat corneal surface irregularities in all patients, even in those not contemplating cataract surgery. However, treating these irregularities prior to cataract surgery is key in order to obtain more accurate measurements of the corneal curvature. Otherwise, it can lead to errors in IOL power selection and orientation of toric IOLs.
The questions of exactly which patients to treat and how to treat them were not addressed in this study. Yet when patients with EBMD and SND are referred to me, as they often are, I take several factors into consideration—all of which may cause continued visual complaints after otherwise successful cataract surgery.
First is the slit-lamp examination: Are there changes related to EBMD or SND within the central 6-7 mm of the cornea? If so, are they visually significant?
This leads to the second consideration: negative staining. After placing fluorescein into the eye, are there elevations of the corneal surface centrally? If so, these correlate with the symptom of blurred vision.
The third consideration is corneal topography. Is there irregular astigmatism? I look at not only the color-coded map but also the Placido ring image. The Placido ring image may be quite distorted, but the color maps may smooth out the irregularities, making the corneal surface appear more regular than it really is.
The authors of this study used superficial keratectomy (SK) and excimer laser phototherapeutic keratectomy (PTK) to treat the corneal irregularities of their patients; however, they did not discuss the specific SK procedure or which eyes received SK versus PTK. I generally perform an SK procedure using a diamond burr polishing technique for patients with EBMD and a PTK for patients with SND. I also typically use adjunctive mitomycin C (0.02% for 60 sec on an 8-mm diameter corneal sponge) in my patients with SND because I believe it decreases the risk of corneal scarring and recurrence of the SND.
The authors also waited a minimum of 30 days before obtaining repeat biometry. I believe it is reasonable to obtain two post-SK/PTK corneal curvature readings to make sure the ocular surface is stable prior to proceeding with cataract surgery.
By addressing these corneal surface irregularities with patients before surgery, we can better manage their postoperative expectations. Otherwise, as surgeons, we run the risk of these problems being ours.
Christopher J. Rapuano, MD, is a nationally and internationally recognized expert in corneal diseases, Chief of the Wills Eye Hospital Cornea Service, and Professor of Ophthalmology at Sidney Kimmel Medical College at Thomas Jefferson University.