We present a new method for identifying the absolute location (i.e., relative to the optic disc) of the preferred retinal location (PRL) simultaneously for the two eyes of patients with central vision loss. For this, we used a binocular eye-tracking system that determines the pupillary axes of both eyes without a user calibration routine.
During monocular viewing, we measured the pupillary axis and the angle between it and the visual axis (angle Kappa) for 10 eyes with normal vision. We also determined their fovea location relative to the middle of the optic disc with the MP-1 microperimeter. Then, we created a transformation between the eye-tracking and microperimeter measurements. We used this transformation to predict the absolute location of the monocular and binocular PRLs of nine patients with central vision loss. The accuracy of the monocular prediction was evaluated with the microperimeter. The binocular PRLs were checked for retinal correspondence and functionality by placing them on fundus photographs.
The transformation yielded an average error for the monocular measures of 0.2 (95% confidence interval, 1.0 to −0.6 degrees) horizontally and 0.5 (95% confidence interval, 1.1 to −0.1 degrees) vertically. The predicted binocular measures showed that the PRLs were generally in corresponding locations in the two eyes. One patient whose PRLs were not in corresponding positions complained about diplopia. For all patients, at least one PRL fell onto functional retina during binocular viewing.
This study shows that measurements of the location of the binocular PRLs relative to the pupillary axes can be transformed into absolute locations.
Vision Science Research Program, Toronto Western Hospital, Toronto, Ontario, Canada (LT-N, ME, MJS, EGG); and Department of Biomedical Engineering (ME), Department of Ophthalmology and Vision Sciences (ME, SNM, MJS, EGG), and Division of Engineering Science (NL-B), University of Toronto, Toronto, Ontario, Canada.
Esther G. González Vision Science Research Program, Toronto Western Research Institute, 399 Bathurst Street, FP 6-212, Toronto, Ontario M5T 2S8 Canadae-mail: firstname.lastname@example.org