Abstract
Abstract: :
Purpose: To determine fixation stability for central and pericentral fixation targets in patients with age–related macular degeneration (AMD). Methods: Six different fixation targets were presented on a high–resolution monitor to 12 patients having late stage AMD involving the fovea (age–range 57 – 87 years) and to 10 age–matched controls having no other eye diseases and visual acuity better than 20/25. The targets were a 1° cross, 1° filled circle, 1° letter ‘x’, small 4 point diamond, large 4 point diamond using dimensions as in the Humphrey Field Analyzer, and a large cross over whole image diagonal with open 1° centre. Prior to examination subjects were given verbal instructions to move their eye in order to see best the centre of the target. Fixation stability was measured for the dominant eye, with the fellow eye occluded, using the SMI gazetracker (SensoMotoric, Germany; Eyelink Software 2.04). Fixation stability was quantified by calculating the bivariate contour ellipse area (BCEA) over 30 sec for each target. In the statistical analysis BCEA values (min of arc2) were converted into their logarithms to better approximate a normal distribution. Absolute retinal scotomata for the study eye were determined using the scanning laser ophthalmoscope (Rodenstock, Germany). Results: Visual acuity in patients ranged from 20/32 – 20/640 (ETDRS chart). Lowest BCEA values were found for the 1° letter ‘x’ in patients (mean 12052.2 ± 254.0%) and for the 1° cross in normal subjects (mean 1286.9 ± 47.8%); highest BCEA values were found for the small diamond in patients (mean 23109.5 ± 298.3%) and for the big diamond in normals (mean 3229.2 ± 105.4%). The difference between the targets was significant for normal subjects (ANOVA p<0.05). In normals, BCEA values were significantly lower for central fixation targets than for pericentral fixation targets (matched–pair t–test). Conclusions: Fixation stability was worse for pericentral fixation than for central fixation targets although the difference was only significant in normal subjects. Our results are important not only for rehabilitation strategies in AMD but also for any other testing method (i.e. psychophysics, multifocal ERG) that requires the patient to maintain stable fixation.
Keywords: eye movements • low vision • aging: visual performance