Exploring fundus-controlled mesopic and scotopic perimetry in inherited retinal disease

Microperimetry is increasingly used as an outcome measure in clinical trials for retinal disease. This study compares mesopic and scotopic microperimetry in a heterogeneous cohort of patients with inherited retinal disease to assess their suitability as clinical trial outcome measures and to determine the most appropriate testing modality.

Participants completed mesopic and scotopic microperimetry (S-MAIA) after 20 min of dark adaptation, as part of the Visual Function in Retinal Degeneration study (ISRCTN24016133). Testing was performed on both eyes (right first) without formal pupil dilation. Reliability and sensitivity performance were explored. A subset of participants (n = 23 patients and n = 16 controls) underwent repeat scotopic testing for repeatability analyses.

Twenty-nine participants with inherited retinal disease and 40 healthy control participants completed microperimetry testing. Mesopic microperimetry in patients and in healthy controls showed good reliability and sensitivity performance. Scotopic microperimetry in patient participants was limited by poor test reliability, reflected by a high number of test exclusions from reliability screening, and significant floor effects in measured sensitivity. In addition, scotopic microperimetry showed no greater improvement in sensitivity or specificity than mesopic microperimetry. Repeatability analyses were limited by the small sample size following elimination of unreliable tests.

Mesopic microperimetry is recommended as a stable and reliable outcome measure. Scotopic microperimetry appears to be limited by poor reliability and floor effects in patients with inherited retinal disease. The utility of scotopic microperimetry in patients with very early disease presentation, who present with highly preserved central vision (i.e. highly preserved mesopic microperimetry), remains unexplored.