Comparison of Photopic and Scotopic Central Retinal Function in Patients With Type 2 Macular Telangiectasia

Abstract

Purpose:: To investigate photopic and scotopic central retinal function in patients with type 2 macular telangiectasia (MacTel) and to compare findings with fundus autofluorescence (FAF) imaging.

Methods:: As part of the MacTel-Study Project, 6 right eyes of 6 patients (median age 69.5 years, range 64-74) with MacTel and visual acuity of 20/40 were included. Using a modified Humphrey field analyser, scotopic and photopic fine matrix mapping (FMM) were performed. Each test consisted of 100 locations on a 9° by 9° matrix of 1° spacing centered at the fixation. Retinal sensitivity was compared with age-matched control values. Furthermore, 10-2 photopic microperimetry (Nidek MP-1) and imaging studies including fundus photography, fluorescein angiography, optical coherence tomography and FAF imaging with scanning laser ophthalmoscopy (exc. = 488 nm, em.>500 nm and exc. = 790 nm, em.>810 nm) were done.

Results:: All patients showed alterations in macular pigment distribution. FMM revealed overall generalized decrease in retinal sensitivity of photopic and scotopic function compared to controls with a median reduction of cone sensitivity of 6.0 dB (Inter Quartile range (IQR) 3.4 -8.0) and a median reduction of rod sensitivity of 7.5 dB (IQR 3.0 - 12.0). Parafoveal pigmented lesions on funduscopy were found to have decreased autofluorescence indicating RPE dysfunction. This correlated with absolute or relatively severe scotoma in microperimetry and FMM. Additional areas of decreased retinal sensitivity shown with both FMM and microperimetry had localized loss of up to 30 dB and were not totally confined to visible angiographic alterations, but showed levels of increased FAF. Scotopic FMM showed larger scotomas and greater loss of sensitivity over these areas compared with photopic FMM.

Conclusions:: Functional testing shows localized retinal dysfunction which extends beyond the region of visible angiographic alterations. The findings suggest that rod function is more severely affected than cone function over areas with reduced retinal sensitivity. Visual acuity testing alone in patients with MacTel may not reflect the actual visual function of the patient and his abilities to cope with daily visual tasks.

Keywords: clinical (human) or epidemiologic studies: natural history • macula/fovea • imaging/image analysis: clinical