Dark-Adapted Two-Color Fundus-Controlled Perimetry in Macular Telangiectasia Type 2

Macular telangiectasia type 2 (MacTel) is a bilateral neurodegenerative disorder of the central macula. Previous findings indicated more functional impairment in low light conditions. We sought to further characterize retinal dysfunction using dark-adapted two-color fundus-controlled perimetry ("scotopic microperimetry").

Participants of the MacTel Natural History Observation Registry study and age-matched healthy controls underwent retinal imaging including dual wavelength autofluorescence macular pigment optical density (MPOD) measurement. Retinal sensitivity was assessed with scotopic microperimetry using cyan (505 nm) and red (627 nm). Disease was graded into classes of MPOD loss (0 to 3). For perimetry analysis, the differences of the mean sensitivities (MacTel minus controls) were compared at each test location and the results were aggregated to global indices.

Thirty-four eyes (19 patients, mean age 62.2 years) were compared with 25 eyes (25 controls, mean age 61.5 years). Both cyan and red sensitivity were lower in MacTel. This was more pronounced at one- and three-degree eccentricity. Eyes with MPOD class 0 did not exhibit a functional deficit. Class 1 had impaired cyan, but normal red sensitivity. Class 2 and 3 behaved similarly and had impaired cyan and red sensitivity with a relatively higher cyan impairment.

Rods might be compromised to a greater extent than cones. Linking to previous studies, our results might also hint toward (postreceptoral) dysfunction of the cone system in very early disease stages. Macular pigment loss and global perimetry indices seemed to reflect functional impairment and might be useful as adjunct measures for disease progression.