Sub-pigment epithelial membranes after photocoagulation for diabetic macular edema
B. K. Rutledge, I. H. Wallow and G. L. Poulsen
Department of Ophthalmology, University of Wisconsin, Madison 53792.
OBJECTIVE--The chronic histopathologic effects of focal and grid argon
laser photocoagulation were examined in eyes obtained at autopsy that had
previously been treated for diabetic macular edema. The focus was on
further characterizing fibrous sub-pigment epithelial membranes that
previously had been shown to extend beyond burn edges. DESIGN--A total of
131 argon laser burns were evaluated in five eyes. Tissue was embedded in
paraffin or glycol methacrylate, serially sectioned, and examined by light
microscopy. MAIN OUTCOME MEASURE--Outer and inner nuclear layer defects
were measured, and the frequency and extent of sub-pigment epithelial
membranes was estimated. The presence of Muller cell processes among
membranes was evaluated by immunostaining for glial fibrillary acidic
protein and enzyme histochemical staining for carbonic anhydrase.
RESULTS--Burns consistently produced defects in the outer nuclear layer
that were larger than the spot size of the laser beam. Inner nuclear layer
defects were present in only seven of 131 burns. Glycol
methacrylate--embedded tissue sections from 73 burns showed sub-pigment
epithelial membranes in all five eyes. In one eye, membranes were confluent
between burns. In the remaining four eyes, 37 individual membranes were
found among 53 burns, and 47% of membranes contained Muller cell processes.
The membranes in paraffin-embedded tissue could not be adequately
evaluated. CONCLUSIONS--After focal laser treatment for diabetic macular
edema, the inner retina was usually spared. Fibrous sub-pigment epithelial
membranes were frequent among burns in all five eyes, and they showed a
conspicuous contribution by Muller cell processes. We speculate that by
impairing the overlying pigment epithelium, these membranes may contribute
to a progressive enlargement of laser scars.
