Abstract

SA.08.02

Fixation stability in type 2 idiopathic macular telangiectasia and its relation to foveal sensitivity, visual acuity and reading speed

Finger R. P., Charbel Issa P., Helb H. M., Holz F. G., Scholl H. P. N.
Department of Ophthalmology, Bonn University, Bonn

Objective: To assess fixation stability and its relation to foveal sensitivity, distance visual acuity, reading acuity and speed in type 2 idiopathic macular telangiectasia (type2-IMT). We have previously shown that patients with type2-IMT may exhibit parafoveal scotomas (ARVO 2006 #5210). We hypothesized that reading acuity and speed may therefore be impaired despite stable central fixation.
Methods: 54 eyes of 27 patients (median age: 63 years; range 49 - 79 years) exhibiting type2-IMT were included. Patients were examined by means of ophthalmoscopy, optical coherence tomography imaging (OCT3) and best-corrected visual acuity (distance with ETDRS charts and reading acuity and speed with Radner charts). Fundus controlled static threshold perimetry was performed with the Nidek MP1. Fixation stability was assessed over a period of 30s and calculated as a Bivariate Contour Ellipse Area (BCEA), within which the centre of the target was imaged 68% of the time. A subgroup of eyes (n=4) were excluded as BCEA could not be calculated due to several preferred retinal loci or a distribution of fixation points other than normal. The BCEAs were analysed using t-tests and correlation analysis.
Results: BCEA in most eyes was within the normal range (mean 665.17 minArc², range 161.53 - 2726.62; reported normal mean for similar fixation target <1286.9 minArc²). Distance VA was reduced in most eyes (mean 20/40; range: 20/200-20/20), as was mean reading acuity (mean 20/50; range: 10/125-20/20) and maximum reading speed (mean 153 words/min). Reading acuity and speed correlated well with distance VA (p=0.01). Foveal sensitivity (mean 14.25 dB; range: 0 - 20) was higher in patients with better fixation stability.
Conclusions: These findings indicate that type2-IMT is associated with functional impairment of reading in late stage disease despite stable central fixation, suggesting that parafoveal scotomas affect this visual function. Reading acuity and speed are good predictors of vision related quality of life, which appears to be threatened in type2-IMT.

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