Fixation stability and scotoma mapping for patients with low vision.

PURPOSE: To develop a simplified device that performs fundus perimetry techniques such as fixation mapping and kinetic perimetry.
METHODS: We added visual stimulation to a near-infrared retinal imager, the laser scanning digital camera (LSDC). This device uses slit scanning illumination combined with a two-dimensional CMOS (complementary metal oxide semiconductor) detector, with continuous viewing of the retina. The CMOS readout was synchronized with the slit scanning, thereby serving as a confocal aperture to reduce stray light in retinal images. A series of retinal images of 36 degrees was automatically aligned to provide data for fixation maps and quantification of fixation stability. The LSDC and alignment techniques also provided fundus viewing with retinal location correction for scotoma mapping.
RESULTS: First, fixation mapping was readily performed in patients with central scotoma or amblyopia. The automatic alignment algorithm allowed quantification of fixation stability in patients with macular pathologies that did not cause scotoma. Second, fixation stability was rapidly and quantitatively assessed by the automatic registration of the series of retina images. There was no significant difference in the fixation stability with automatic versus manual alignment. Kinetic perimetry demonstrated that fundus imaging helped reduce the variability of perimetric data by identifying and preventing false-positives caused by eye motion. We found that the size of the blind spot was significantly larger for dark targets on brighter backgrounds than when the contrast was reversed (p < 0.045). This is consistent with incremental targets being detected partially or wholly because of scattered light falling on more sensitive retinal locations.
CONCLUSIONS: Fundus perimetry with the LSDC allows for a wide range of fixation and perimetry tasks.