Clinical research performed by the Department of Ophthalmology, University of Bonn, Germany, has shown that microperimetry assessment in patients suffering macular telangiectasia type 2 (MacTel2) may be significantly more sensitive in detecting functional decline than the standard optotype BCVA tools. In addition, the research suggested that microperimetry may provide a more accurate readout in assessing functional outcome measures in future clinical trials. While the prevalence of MacTel type 2 may be as high as 0.1% in the >40 year old population, the actual true prevalence may be significantly higher if measured by the more sensitive microperimetry approach.
Macular telangiectasia type 2 is well characterized as a bilateral macular disease with vascular changes and outer retinal atrophy causing functional visional loss. Patients generally report initial symptoms in their 50s and 60s manifesting as impaired visual function, diminished reading ability, metamorphopsia, and worsening visual acuity. The first clinical study (a Phase 1 safety trial) evaluating an experimental treatment for MacTel 2 has recently being reported in the American Journal of Ophthalmology (2015;159:659–666). However, few natural history studies allow conclusions on meaningful functional outcome measures. According to the authors of the microperimetry assessment, “[T]he most commonly used endpoint of therapeutic studies for retinal disease has been single optotype BCVA, a parameter that largely depends on central foveal function. In MacTel type 2, however, functional decline typically initially spares the foveal center. Thus, other clinical parameters may be needed to monitor paracentral loss of function so as to evaluate disease progression and/or therapeutic effects.”
In assessing the value of microperimetry, the German research group conducted a prospective longitudinal observational study measuring the change of cumulative defect size (number of test points with absolute scotoma) and the change in distance BCVA. Results of the study showed that patients with MacTel type 2 undergo a progressive focal loss of macular sensitivity, preceded by a loss of visual acuity. As such, according to the authors, microperimetry “may provide considerable power when being used as a functional outcome measure”. In their study, microperimetry revealed a spread (n = 31) or new development (n = 10) of an absolute scotoma in 58% of 71 eyes (40 patients). Simultaneously, BCVA decreased more than two lines in only 17% (n = 12) of the patients. 35% of the eyes showed no change in visual function. Eyes with an absolute scotoma at baseline (n = 33) showed further growth of the scotoma in 94% of cases (n = 31) while, only 26% (n = 10) of eyes without an absolute scotoma at baseline (n = 38) developed a new absolute scotoma. According to the researchers, presence of an absolute scotoma at baseline, but not baseline BCVA, was predictive for functional decline on longitudinal microperimetry testing. Finally, the research group recorded that scotomata always first occurred in the quadrant temporal to the foveal center.