Subfoveal neovascular membranes in senile macular degeneration: Relationship between membrane size and visual prognosis

Neovascular membranes that lie under the geometric center of the foveal avascular zone are larger than neovascular membranes completely outside the foveal avascular zone. Thirty-eight (66%) of 58 subfoveal membranes were greater than 1500 microns in diameter while only seven (12%) of 58 extrafoveal membranes were greater than 1500 microns (P<.000001). Of all eyes with subfoveal membranes and an initial visual acuity of 20/100 or better, acuity remained the same or improved in 5 (38%) of 13 eyes with small membranes and in none (0%) of 13 eyes with large membranes (P < 0.02) after an average follow-up of 22 months. Furthermore, nine (70%) of the 13 eyes with large membranes and an initial visual acuity of 20/100 or better were 20/200 or worse at follow-up. For eyes whose initial visual acuity was 20/126 or worse, a statistically significant difference could not be demonstrated in the visual prognosis between eyes with small vs large membranes. Nevertheless, all but one of these eyes remained 20/126 or worse at follow-up, including 80% that were 20/200 or worse at follow-up regardless of membrane size. Because of the uniformly poor visual prognosis for eyes with large subfoveal membranes, a randomized trial of krypton red photocoagulation seems justifiable if careful low-vision assessments are done before and after the trial.