Feasibility of microperimetry testing at multiple sites in type 2 idiopathic macular telangiectasia

Abstract

Purpose: Macular telangiectasia type 2 (MacTel) causes significant functional visual loss which can be mapped by microperimetry (MP1). Five out of the 27 centers of the worldwide MacTel Natural History Observation Study systematically performed MP1 examinations at baseline and during the follow-up. Here we report the MP1 baseline characteristics of this MacTel sub-population.

Methods: A total of 544 eyes of 272 participants had the MP1 exam at baseline. All MP1 exams were performed under mesopic conditions using predetermined testing grids. All printouts were sent to the Moorfields Reading Centre for data entry and analysis. Retinal thresholds and fixation characteristics were analyzed. Best corrected visual acuity (BCVA) was determined and correlated to MP1 data.

Results: 169(62%) of the participants were females and the average age of all patients was 61.1±9.1 years. Of the 544 potential eyes 527 were completed and therefore could be analyzed. Most patients (74%) took less than 15 minutes per eye to complete the test. On average, reliability was 82%. Of those with available data, 59% of eyes had stable, 30% relatively unstable and 11% unstable fixation (n=291 eyes). Fixation was central in 78% of eyes, relatively eccentric in 15% and eccentric in 7%. BCVA was best in the stable group, and the worst in the unstable fixation group (74.3 letters, Snellen equivalent of 20/30) vs 61.2 letters (Snellen ~20/60), p<0.001). Analysis for the presence or absence of scotomas could be completed in 96.5% of cases. Scotomas were present in 49%, of those 71% were absolute and in the temporal area. Relative scotomas were present in 53% and these were also predominantly located temporal of the fovea.5% of absolute and 3% of relative scotomas involved the fovea. Functional impairment starts at the same temporal region as for other components of the disease.

Conclusions: Microperimetry provided valid and comparable data on visual function in patients with MacTel, strengthening our knowledge of functional impairment both in early and late stages of the disease. Further investigation is required as to which grid pattern is the best and how impairment progresses during the course of the disease.

Keywords: 550 imaging/image analysis: clinical • 585 macula/fovea • 465 clinical (human) or epidemiologic studies: systems/equipment/techniques