"EDTA chelation can be done in the office or concurrently with other ocular surgery if needed, and compared with use of phototherapeutic keratectomy (PTK), EDTA chelation is much less expensive and avoids changes in corneal thickness that can lead to refractive error," said Dr. Dunn, associate professor of ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore.
Band keratopathy can occur as a complication of a number of disorders. Its development in eyes with chronic uveitis is often seen in pediatric patients. In addition, it occurs in eyes with hypotony, phthisis bulbi, dry eye, or post-silicone oil injection. Band keratopathy can also develop in association with various hereditary and metabolic disorders affecting calcium or phosphate homeostasis or as a complication of certain topical drugs containing phosphates or preservatives that bind calcium.
"Addressing contributing causes when possible is an essential component of managing band keratopathy. EDTA chelation has a role for removing calcium deposits that are interfering with visual function or causing ocular irritation," Dr. Dunn said.
Although there are reports of EDTA chelation being performed at the slit lamp, because of the pain involved, Dr. Dunn prefers to use retrobulbar anesthesia.
When the deposits are only being removed centrally to improve vision, the visual axis is first marked with a trephine, usually at about 6 mm, and then the corneal epithelium is removed with scraping to allow penetration of the EDTA to the subepithelial layer where the calcium lies. However, Dr. Dunn cautioned not to scrape Bowman's layer because that maneuver can cause irregularity and worsen the postoperative results.
For the chelation, Dr. Dunn uses a solution of disodium EDTA 26.2 mg/ml applied into the trephine well.
"We think it is important to maintain well-demarcated epithelial borders because that technique seems to hasten re-epithelialization and also to use an adequate concentration of EDTA. In addition, be sure not to use calcium EDTA because it will only exchange calcium for calcium and not be effective," Dr. Dunn said.
He noted the EDTA concentration he uses is somewhat higher than is reported by other cornea specialists. Dr. Dunn credited Ivan Schwab, MD, at University of California Davis, for suggesting the 26.2 mg/ ml solution.
"Dr. Schwab says in his experience using this concentration, he has never had to scrape calcium off the eye," he said.
The EDTA solution is applied over the eye in a vial with attention to minimizing exposure of unaffected tissue.
"We prefer not to use an approach that saturates the entire eye because it irritates the peripheral cornea and conjunctiva and leads to delayed healing. In most of our patients, visual loss, not discomfort, is the indication for removing the calcium, and so peripheral band keratopathy does not need to be treated," he explained.
If, however, patients are experiencing irritation of the conjunctiva from elevated calcium deposits in the periphery, those need to be excised and the EDTA solution should be applied more peripherally.
The EDTA solution is held in place for a few minutes. Then the eye is irrigated, and the application repeated as needed. An EDTA-saturated Weck-cel sponge can also be rubbed over areas of highly adherent calcium. Postoperative care includes patching for 24 to 48 hours.
With maintenance of well-demarcated epithelial borders, the majority of patients achieve full re-epithelialization within 2 to 3 days. Aggressive postoperative lubrication is also used to promote healing.
Dr. Dunn said that cornea specialists from Wills Eye Hospital recently reported their experience using 37.5 mg/ml EDTA at the slit lamp to treat band keratopathy [Najjar DM, et al. Am J Ophthalmol 2004; 137:1056-1064]. In their series, the mean and median times to re-epithelialization were 8 days and 4 days, respectively.