A total of 53 adult subjects participated in the study; 13 subjects with either dry or wet AMD, 20 young control subjects with normal vision, and 20 older control subjects with normal vision. The normally-sighted subjects were recruited from the local community or through a relationship with another subject. The AMD subjects were recruited from the Indiana University School of Optometry's Primary Care and Vision Rehabilitation Service clinics. Significant differences in age existed between the normally-sighted and AMD subject groups (1-way ANOVA, F(2,52) = 681.20, P < 0.001). As expected, the young normally-sighted subjects were significantly younger than the older normally-sighted (independent t-test, t(1,38) = 29.36 P < 0.001) and AMD (independent t-test, t(1,31) = 24.98, P < 0.001) subjects. The older normally-sighted subjects did not differ in age from the AMD subjects (independent t-test, t(1,31) = −0.15, P = 0.89).
Three visual functions were assessed in each subject: VA, CS, and VF. The average results of these assessments for all three subject groups are presented in
Table 1.
Each subject's binocular VA was assessed using an Early Treatment Diabetic Retinopathy Study (ETDRS) acuity chart,
19 which was transilluminated to approximately 100 candela/m
2 (cd/m
−2). Each subject's threshold binocular VA was reported as the logarithm of the minimum angle of resolution (log MAR) using the scoring of Bailey et al.
20 As expected, significant differences in binocular VA were found across the groups (1-way ANOVA,
F(2,52) = 36.40,
P < 0.001). Specifically, the young normally-sighted subjects had significantly better binocular VA than either the older normally-sighted (independent
t-test,
t(1,38) = 6.03,
P < 0.001) and AMD (independent
t-test,
t(1,31) = 5.18,
P = 0.0002) subjects, and the AMD subjects had significantly worse binocular VA than the older normally-sighted subjects (independent
t-test,
t(1,31) = 3.69,
P = 0.003).
A Pelli-Robson letter contrast sensitivity chart
21 positioned at 1 m with overhead illumination of 85 cd/m
−2 was used to measure the binocular CS in each subject. The binocular threshold log CS was determined using the scoring of Elliott et al.
22,23 Significant differences in the binocular CS were found across groups (Kruskal-Wallis 1-way ANOVA, χ
= 34.96,
P < 0.001). The binocular CS of the young normally-sighted subjects was significantly better than the older normally-sighted (Wilcoxon rank sums test,
z = −4.51,
P < 0.0001) and AMD (Wilcoxon rank sums test,
z = −4.95,
P < 0.0001) subjects. The binocular CS of the AMD subjects was significantly worse than the older normally-sighted subjects (Wilcoxon rank sums test,
z = −3.12,
P < 0.0001).
Kinetic perimetry was performed on each subject using a Goldmann bowl perimeter (III4e target on a background luminance of 10 cd/m−2) to assess monocular VFs along 24 meridians from radii of 700 vertically and 900 horizontally. Located inside the bowl of the Goldmann perimeter was a central target on which subjects were instructed to fixate. The AMD subjects were instructed to use eccentric fixation, presumably with their preferred retinal locus (PRL), during the VF assessment. VF extent and the position of any central scotomas were recorded for all subjects. The average VF extent (radius) in each eye was computed for each subject by averaging the VF extent along each meridian. The eye that had the greatest average VF extent (radius) was reported as the average VF extent (radius) in the better eye. Significant differences in the average VF extent (radius) in the better eye were found across the groups (1-way ANOVA, F(2,51) = 17.16, P < 0.001). Specifically, the young normally-sighted subjects had a significantly larger average VF extent in the better eye than either the older normally-sighted (independent t-test, t(1,38) = −6.15, P < 0.001) and AMD (independent t-test, t(1,31) = −3.90, P = 0.002) subjects. The average VF extent in the better eye of the AMD subjects did not differ from the older normally-sighted subjects (independent t-test, t(1,30) = 0.11, P = 0.92).
The extent, position, and size of any central scotomas within the central 300 radius VF along 12 meridians was also assessed in all subjects' right and left eyes using a Bjerrum (tangent) screen with a 5/1000 W Traquair target. The Bjerrum (tangent) screen had a screen illuminance of 112 lux. Subjects wore their own distance prescription and were instructed to fixate on a large, centrally located letter “E” target. The AMD subjects were instructed to use eccentric fixation, presumably with their PRL, during the VF assessment. The average radius of the scotoma in each eye, in degrees, across the eight principal meridians of the scotoma were computed. The eye that had the smallest average scotoma (radius) was reported as the average scotoma size (radius) in the better eye. As expected, the age-matched younger and older normally-sighted subjects had no central scotomas, while five of the 13 AMD subjects had a scotoma in the better eye that was on average (SD) 1.440 (2.210) in radius.
For this study, subjects were required to self-report being independent travelers who regularly crossed streets unaided and who self-reported having no history of a physical disorder that affected their walking abilities. Subjects also were required to have good cognitive function as determined by obtaining a score of 24 or greater on the Mini-Mental State Exam (MMSE).
24 All subjects were unfamiliar with the intersection used in the study.
Informed consent was obtained from each subject after the nature and possible consequences of the study were described. The study followed the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of Indiana University.