Abstract
Purpose :
The aim of this study was to determine the accuracy of the visual field of view claims by low vision telescope manufacturers for commonly prescribed telescopes in a setting that can be easily duplicated in a clinical Low Vision practice.
Methods :
The useful visual fields of 20 telescopes were determined based on measurements in one observer which had an intact visual field. The visual fields were measured by the investigator as dynamic visual fields using a tangent screen set up at 2, 4, and 6 meters and a standardized Goldmann target size of 2mm. To avoid experimental bias, the manufacturer-stated fields of view were not known by the investigators prior to concluding all measurements. Statistical analysis was conducted using repeated-measures ANOVA with Dunnett’s multiple comparisons test and a P value of < .05 was considered statistically significant. A difference of more than 1 degree was considered clinically meaningful.
Results :
Statistically significant differences were found between the manufacturer-stated visual field angles and the measured field angles for measuring distances of 2 m (P = .0.0004) and 4 m (P = 0.0.0183), but not for 6 m (P = 0.1431).
At 2 m, the measured visual field angles (mean 13.12 degrees, SD 3.802) were substantially larger than the manufacturer-stated visual field angles (mean 11.08 degrees, SD 3.163). This difference was clinically meaningful.
At 4 m, the measured visual field angles (mean 12.41 degrees, SD 3.766) were substantially larger than the manufacturer-stated visual field angles (mean 11.08 degrees, SD 3.163). This difference was clinically meaningful.
At 6 m, the measured visual field angles (mean 11.88 degrees, SD 3.449) were slightly larger than the average of the manufacturer-stated visual field angles (11.08 degrees, SD 3.163). This difference was considered clinically not relevant.
Conclusions :
For the 20 measured telescopes, the manufacturer-stated field angles are appropriate for a distance of 6 m. At shorter distances of 2 m and 4 m, the manufacturer-stated visual field angles underestimate the measured visual field angles. Since telescopes are inherently designed for seeing distant objects, the manufacturer-stated visual field angles are reliable.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.