Mega Lenses After Glaucoma Filtration Surgery

BY ROBERT CAMPBELL, M.D. & PATRICK CAROLINE, C.O.T., F.A.A.O.
APR. 1997

The major goal of all glaucoma filtering procedures is to surgically connect the anterior chamber of the eye with the subconjunctival space. Surgery results in the formation of a filtering bleb, which is a subconjunctival accumulation of aqueous. Intraocular pressure is maintained by the controlled diffusion of aqueous through the conjunctival tissue (Fig. 1).

FIG. 1: BLEB FOLLOWING GLAUCOMA FILTERING PROCEDURE.

Today, glaucoma filtering procedures include trabeculectomy, sclerostomy, laser sclerostomy and seton implants. One of the major complications of all filtering procedures is uncontrolled or excessive filtration. This can result in hypotony and a shallow anterior chamber in up to 13 percent of cases, or a flat anterior chamber in three percent to four percent of cases. Historically, excessive filtration has been controlled by a variety of procedures: viscoelastic injection, resuturing, pressure patching, cyanoacrylate glue, conjunctival resection and PMMA scleral shells.

A NEW OPTION TO CONTROL FILTRATION

In 1994, James McAllister, M.D., of Windsor, U.K., and Flexlens of Englewood, Colo., codeveloped a new, large-diameter, soft contact lens to control excessive filtration. The McAllister lens is designed with sufficient peripheral rigidity (thickness) to control excessive filtration or leakage by applying pressure over the bleb (Fig. 2), thereby reducing the risk of flat or shallow anterior chambers. The lens is available in three designs and two water contents, 45 percent and 55 percent (Table 1).

FIG. 2: THE MCALLISTER GLAUCOMA FILTRATION CONTROL LENS.

EXCESSIVE FILTRATION POST TRABECULECTOMY

This month's case history involves a 64-year-old man with bilateral open-angle glaucoma. He had been treated with maximum topical and systemic medications as well as argon laser trabeculoplasty, but the intraocular pressure of the left eye had remained uncontrolled. Eventually, the patient underwent a trabeculectomy.

At the one-day postop visit, the surgeon noted a flat chamber due to excessive filtration. A McAllister lens was immediately applied, base curve 9.50mm, plano power, 19.5mm diameter, and the eye was patched overnight (Fig. 3). Upon 24-hour evaluation, the anterior chamber was well-formed and the intraocular pressure was 4mmHg. The patient wore the lens without a patch for an additional 24 hours, at which time the pressure increased to 8mmHg. The lens was removed and the pressure stabilized without recurrence of excessive filtration.

FIG. 3: THE MCALLISTER LENS ON THE EYE.

This case history illustrates the effective use of large diameter bandage lenses following filtration surgery. These larger 'mega' lenses have also been used as bandage lenses in cases involving conjunctival trauma, scleral patch grafts, superior limbic keratoconjunctivitis and Mooren's ulcer. CLS

Dr. Campbell is medical director of the Park Nicollet Contact Lens Clinic & Research Center, Minnetonka, Minn. Patrick Caroline is an assistant professor of optometry at Pacific University, Forest Grove, Ore., and director of contact lens research at Oregon Health Sciences University in Portland.