Session Title: Free Paper Session 12: Imaging I
Session Date/Time: Friday 08/09/2017 | 14:30-16:00
Paper Time: 15:12
Venue: Room 111
First Author: : T.Heeren INDIA
Co Author(s): : S. Mueller R. Bonelli M. Okada M. Pfau C. Egan F. Holz
Macular telangiectasia type 2 (MacTel) is a disease of allegedly neurodegenerative origin. Recent research suggests involvement of Müller cells and early deterioration of rod integrity. We sought to identify early functional changes that might lead to earlier identification of affected patients and help to understand the disease pathomechanism. Further, identification of other functional tests than best corrected visual acuity (BCVA) might aid to define outcome measures in investigational trials.
Two centre study (Moorfields Eye Hospital, London, UK, and University Eye Hospital, Bonn, Germany) as part of the MacTel natural history and observation study (NHOS) group. Participants from the NHOS were selected randomly and invited to take part in this substudy.
The disease was classified into early disease on one hand, and advanced disease on the other hand, based on the presence of absolute scotomata in mesopic microperimetry and/or loss of BCVA to 20/50 or more. After signing informed consent for the substudy, a first group underwent extensive testing in photopic, mesopic and scotopic conditions in one centre: BCVA was tested following the European Treatment of Diabetic Retinopathy Study (ETDRS) protocol. Low luminance visual acuity (LLVA) was tested using the same protocol with an additional 2.0 log unit neutral density filter placed in front of each eye. The difference between BCVA and LLVA was defined as low luminance deficit (LLD). Contrast sensitivity was tested with Pelli Robson charts in photopic and mesopic conditions (mean room illumination of 110 lux and 1 lux, respectively). Finally, microperimetry (sMAIA, centrevue, Padova, Italy) was performed under both mesopic and scotopic conditions (<0.1 lux) using a radial testing pattern with test points at one, three, five and seven degrees eccentricity from the foveal centre. A second patient group with early disease was tested in both centres with a testing grid of higher spatial resolution.
The first group with extensive testing (n=21 patients) was compared to an age and gender matched control group (n=17). The second group with refined microperimetry testing pattern (n=20 patients) was compared to normal values computed from a normative database using spatial interpolation. LLVA, but not BCVA, was significantly lowered in both early and advanced disease. Contrast sensitivity was reduced in advanced stages under both photopic and mesopic conditions. In early stages, contrast sensitivity was reduced only in mesopic conditions. In microperimetry, scotopic function was more impaired than mesopic function, but was confined to the 'MacTel area'. This effect was seen in both early and advanced disease stages. Moreover, scotopic functional impairment was found in areas without evident mesopic functional loss. In the second group tested with higher spatial resolution, scotopic sensitivity reduction was predominantly found in the temporal parafovea.
Retinal function in MacTel seems to be dependent on ambient light conditions. Our results show that contrast sensitivity and BCVA are more compromised under mesopic than photopic conditions. Under scotopic conditions, retinal function seems to deteriorate further. This finding suggests more compromised rod than cone function in keeping with previous functional and histological studies. Further, the reduction of retinal sensitivity in scotopic but not mesopic conditions in early stages indicates impaired rod function as possibly earliest functional sign in MacTel. Easily performed tests such as low luminance visual acuity, or contrast sensitivity under mesopic illumination might reveal functional deficits earlier than standard tests, and therefore offer viable tests for routine clinics. Scotopic microperimetry as more advanced psychophysical method seems promising for quantification of the extent of functional loss and might offer a functional outcome measure for future investigational trials especially in early disease stages.