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Elli J. Kollbaum, Christopher A. Clark, Matthew S. Muller, Benno L. Petrig, Bryan P. Haggerty, Ann E. Elsner; Scotoma Mapping with the Laser Scanning Digital Camera Stimulator. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4366.
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To improve the mapping of scotomata by mapping the location of the visual stimuli on a high quality and real-time image of the retina. To use the mapping of the blind spot to optimize parameters for scotoma mapping, from the wide range of parameters available on a new device, the Laser Scanning Digital Camera Stimulator (LSDC-S). To test whether decremental targets reduce false positives and increase the size of the blind spot map, compared with incremental targets, in which scattered light from the target may be detected at high stimulus contrasts.
6 subjects, 1 female and 5 males ages 33 - 61 yr were selected to provide a wide range of refractive error and age. The LSDC-S is a slit scanning imager that provides a high contrast, continuous 36 deg retinal image 850 nm, at 2 mW at the cornea. The visual stimuli were projected by a digital light projector in Maxwellian view, with stimulus focus linked to retinal image focus, thereby minimizing artifacts from both the subject’s pupil size and spherical error. We compared the map of the blind spot, as well as false positives, across target size, incremental vs. decremental targets, direction of motion, and target speed. Kinetic perimetry was tested at standard speeds, 2.5 - 5 deg/sec and lower to reduce response time artifact. The target sizes were in 3 steps, roughly Goldmann II to III. We tested a variety of incremental targets on dim backgrounds and decremental targets on brighter backgrounds (black on white). Presenting the contrast used in Goldmann perimetry, 1.5 log unit, did not require the full dynamic range of the available stimuli.
The LSDC-S, which presents stimuli and images through a small pupil size, provided retinal images even with bright backgrounds. False positives due to incorrect retinal position were determined from the retinal images, while correct detection on tilted optic nerve heads was not mistaken as a false positive. As expected, the size of the blind spot depended upon target size and speed, with reduced speeds improving the accuracy of mapping the blind spot. The blind spot was measured as larger with black target on white background than with a white target on black background (p = 0.045.)
The LSDC-S provides a full range of stimuli that reduce the potential for ceiling or floors effects, and improve accuracy by reducing the variability among subjects due to pupil size or target focus, and reducing false positives due to eye motion or speed.
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