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Fixation stability using central and pericentral fixation targets in patients with age-related macular degeneration
Caren Bellmann1, Mary Feely, Michael D Crossland
1Institute of Ophthalmology, London, United Kingdom.
Purpose:
To determine fixation stability for central and pericentral fixation targets in patients with age-related macular degeneration (AMD).
Design:
Comparative study.
Participants:
Twelve patients having late-stage AMD involving the fovea and 10 age-matched controls having no other eye diseases and visual acuity better than 20/25.
Methods:
Six different fixation targets (1 degrees cross; 1 degrees filled circle; 1 degrees letter x; small 4-point diamond; large 4-point diamond using dimensions as in a field analyzer; large-crossover whole-image diagonal with open 1 degrees center) were presented on a high-resolution monitor. Before examination, subjects were given verbal instructions to move their eye to see the center of the target best. Fixation stability was measured for the preferred eye, with the fellow eye occluded, using a gaze tracker. Fixation stability was quantified by calculating the bivariate contour ellipse area (BCEA) over 30 seconds for each target. For statistical analysis, BCEA values (minutes of arc2) were converted into their logarithms. The absolute retinal scotoma for the study eye was determined using a scanning laser ophthalmoscope.
Main Outcome Measure:
Bivariate contour ellipse area.
Results:
Visual acuity in patients (age range, 57-87 years) ranged from 20/32 to 20/600. The lowest BCEA values were found for the 1 degrees letter x in patients (mean, 12052.2%+/-254.0%) and for the 1 degrees cross in normal subjects (mean, 1286.9%+/-47.8%); the highest BCEA values were found for the small 4-point diamond in patients (mean, 23109.5%+/-298.3%) and for the large 4-point diamond in normals (age range, 62-79 years) (mean, 3229.2%+/-105.4%). The difference between the targets was significant for normal subjects (analysis of variance [ANOVA], P<0.01) but not for patients (ANOVA, P>0.05). In normals, BCEA values were significantly lower for central fixation targets than for pericentral fixation targets (P<0.01).
Conclusion:
Fixation is significantly less stable for pericentral fixation targets in normal subjects, indicating an advantage for central fixation targets. These results are particularly significant for any clinical and experimental testing method that requires the patient to maintain stable fixation.
