Hypotony maculopathy reversible if repaired early enough

Miami-Hypotony maculopathy is a fixable problem if it is repaired within 6 months, according to Paul F. Palmberg, MD, PhD.

Reduced vision with hypotony can be divided into two forms: variable refraction from low pressure or hypotony maculopathy with chorioretinal folds, said Dr. Palmberg, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine. As first pointed out by J. Donald M. Gass, MD (who named the condition), hypotony maculopathy is caused by the contraction of elastic sclera in a hypotonous eye after filtering surgery, or surgical or traumatic cyclodialysis.

The risk factors are young age, associated with a more elastic sclera; myopia, in which the sclera is thinner; and a particularly low IOP.

"I prefer to fix it promptly, within a week or two if it is not improving, because you want to restore the vision, allay anxiety, and avoid the formation of retinal fibrosis," Dr. Palmberg continued.

He added that treatments such as cataract surgery or intrableb blood injection rarely are effective in reversing hypotony maculopathy.

Repair surgery goals

The two goals of repair surgery for hypotony maculopathy are to raise the IOP temporarily enough to flatten the folds in the retina and then to save the bleb with a good target pressure.

"I only know one way to do that, which is to reoperate and use two sets of stitches in the scleral flap," Dr. Palmberg said.

One set of sutures adjusts the IOP at equilibrium flow to a target pressure of 8 to 10 mm Hg, and the second set adjusts the IOP to about 20 to 25 mm Hg to stretch the sclera temporarily and flatten the chorioretinal folds.

The flattening takes 1 to 4 weeks, after which the second set of sutures is cut by laser suture lysis to reduce the IOP to the target pressure set by the first set of stitches. The first set should be preserved if possible to avoid recurrence of hypotony, he explained.

Scleral compression stitches or patch grafts may be needed in some cases. Horizontal 10-0 nylon mattress stitches may be placed over the scleral flap or tunnel to increase resistance in those cases in which the alternative of using increasingly tighter stitches in the scleral flap would risk making claw holes (that create leaks) or risk creating significant astigmatism.

Dr. Palmberg has repaired several referred cases in which a large, thin scleral flap had been used, and the flap had melted after several years.

"If you use short, stubby scleral flaps or tunnels, such scleral melting is very rare," he said.

When melts are encountered at re-operation, Dr. Palmberg has used half-thickness scleral or corneal patch grafts held in place by bungee-cord-like 10-0 nylon compression stitches, anchored to each side of the defect.

The visual results of the two sets of stitches that he devised to flatten chorioretinal folds have been very good, Dr. Palmberg said. A formal analysis of the first 26 cases found that vision had improved in all patients. Mean vision improved from 20/100 to 20/25, average IOP increased from 2 mm Hg to 14 mm Hg, no blebs were lost (although one was lost in a subsequent patient), and 25 of 26 cases had resolution of metamorphopsia.

No patient was found to have suffered visual field progression during the few weeks of moderately elevated IOP required to flatten the macular folds. Two patients in the initial cohort had a late recurrence, as did two later patients, requiring further surgery.

Hypotony maculopathy is seen with 5-FU filtering surgery and more commonly with MMC use, with an incidence of 3% to 14% in primary filtering surgery and 1% to 5% in complex filtering surgery. It may also occur with hypotony caused by a cyclodialysis cleft.

"It should be understood that MMC and 5-FU never cause hypotony. However, they will certainly preserve any hypotony you create, very effectively and for a long time," he said.