Abstract
Purpose: :
To develop and evaluate two caps to control the luminance and diameter of the output of a standard laser pointer (stimulus) used in a manual central visual field test when administered to subjects with wet age-related macular degeneration (AMD).
Methods: :
The Fletcher Central Visual Field (FCVF) test was administered on one eye of 8 subjects using a laser pointer with two different caps which altered the luminance of the stimulus. The first administration utilized a cap with a 1mm opening (cap1) and the second administration utilized the same cap combined with a 0.3 log neutral density filter (cap 2). The resulting scotomas were plotted on an 8.5"X11" recording sheet held at 57cm according to test instructions. Each set of scotomas (isopters) was quantified in area (mm2) using Scion tracing software and then compared for statistical significance. Inclusion criteria included >20/60 visual acuity, wet AMD and a history of a central scotoma based on chart review.
Results: :
A Wilcoxon signed rank test was performed to determine if scotoma areas were different using the two caps. The scotomas plotted using the filtered stimulus (cap #2) were larger by 32115 mm2 on average (increase of 7X) (P=0.011). Upon further analysis, 4 of the 8 subjects had an initial scotoma that increased in area by16,787 mm2 (increase of 1.8X) (p=0.05) and the second scotoma was still contained within the recording sheet. The other four varied in results: three were without initial scotoma (cap 1) but then had either a very large scotoma with two of the borders extending to the edge of the recording sheet or the stimulus (cap 2) could not be seen at all. One had a small scotoma and then could not see the second stimulus (cap 2).
Conclusions: :
Several levels of luminance and size of the laser emission can allow for more sensitivity in plotting relative scotomas that are not dense but are still clinically significant. Within a small sample, the customized stimulus caps were effective in identifying two isopters when using the modified tangent screen (Fletcher Central Visual Field Test). With the test performed at 57 cm, each cm corresponds to 1 degree and therefore the recording sheet can enable manual perimetry over approximately 28 degrees horizontally and 21.5 degrees vertically. With four of the subjects having variable results with cap 2, it seems that further testing and development of the caps (modifying the neutral density filter or the size of the opening) may improve upon this convenient clinical test.
Keywords: low vision • age-related macular degeneration • visual fields