Purpose: To investigate progressive vision loss in patients with macular telangiectasia (MacTel) type 2 and to compare the ability to detect functional decline between microperimetry and visual acuity testing.
Methods: Change of cumulative defect size (number of test points with absolute scotoma) on microperimetry testing and change in distance best-corrected visual acuity (BCVA) were evaluated in a prospective longitudinal observational study.
Results: The mean review period was 55.3 months (SD 17.3 months). In 58% of 71 eyes (40 patients) included for analysis, microperimetry revealed spread (n = 31) or new development (n = 10) of an absolute scotoma. At the same time, BCVA decreased more than two lines in only 17% (n = 12). Twenty-five (35%) eyes showed no change in visual function. Presence of an absolute scotoma at baseline, but not baseline BCVA, was predictive for functional decline on longitudinal microperimetry testing. Eyes with an absolute scotoma at baseline (n = 33) showed further growth of the scotoma in 94% (n = 31). In contrast, only 26% (n = 10) of eyes without an absolute scotoma at baseline (n = 38) developed an absolute scotoma de novo. Scotoma growth rate (new test points with an absolute scotoma per year) was 0.62 ± 0.10 for all eyes and 1.30 ± 0.12 for the subgroup of eyes with scotoma at baseline. Scotomata always first occurred in the quadrant temporal to the foveal center.
Conclusions: A characteristic feature in patients with MacTel type 2 is progressive focal loss of macular sensitivity, preceding loss of visual acuity. Microperimetry is sensitive to detect such functional decline and thus may provide considerable power when being used as a functional outcome measure in future clinical trials.