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

Abstract

PURPOSE. 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 twocolor fundus-controlled perimetry (''scotopic microperimetry''). METHODS.Participants of the MacTel Natural History Observation Registry study and agematched 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.RESULTS. 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.CONCLUSIONS. 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.

Impairments of L-Cone/M-Cone and S-Cone–mediated Color Discrimination in Macular Telangiectasia Type Ii

“…However, these alterations are comparatively subtle compared with the profound alterations in paracentral cone–mediated and rod-mediated threshold sensitivity. 20 , 21 In contrast to other conditions affecting the paracentral retina, 18 , 19 loss of S-cone–mediated discrimination does not appear to be a prominent feature of MacTel. However, as noted above, losses in S-cone–mediated sensitivity may be offset by decreases in macular pigment optical density, which are a characteristic of this condition.…”

Clinical Perspectives and Trends: Microperimetry as a Trial Endpoint in Retinal Disease

“…The concept of using 2 wavelengths of stimuli was first established in modified perimeters to isolate photoreceptor function by exploiting the difference in spectral sensitivity of rods and cones [53, 54]. Generally, under fully dark-adapted conditions in healthy retina outside the rod-free zone, rods are more sensitive than cones at both wavelengths and, secondly, the sensitivity to cyan is much higher (around 2 log units) than for red stimuli [53].…”

“…Generally, under fully dark-adapted conditions in healthy retina outside the rod-free zone, rods are more sensitive than cones at both wavelengths and, secondly, the sensitivity to cyan is much higher (around 2 log units) than for red stimuli [53]. The scotopic setting of the S-MAIA has been calibrated according to the CIE 1951 scotopic luminosity function or V’(λ) such that the radiance of a sensitivity value for scotopic cyan stimuli is in effect 20 dB lower than that for red [54]. Therefore, a cyan-red difference of around 0 dB (in areas outside the rod-free zone and in the presence of normal sensitivity values for cyan and red), indicates normal rod function in the S-MAIA [52].…”

Impairments in Cone Pigment Regeneration and Absolute Threshold in Macular Telangiectasia Type 2

“… 9 However, it should also be noted that newer paradigms, such as scotopic microperimetry, may address the issue of rod isolation. 10 …”

“…9 However, it should also be noted that newer paradigms, such as scotopic microperimetry, may address the issue of rod isolation. 10 We aimed to explore the hypothesis that there is a dysfunction of light adaption in the cone photoreceptors in MacTel. Evidence accrued over the last decadeand-a-half suggests that although the canonical visual cycle of chromophore regeneration is retinal pigment epithelium dependent, this process is slow and possibly more critical for the rods than the cones.…”