Binocular versus monocular viewing in age-related macular degeneration
Purpose: This thesis compares monocular versus binocular viewing in AMD patients during fixation and reading, the potential of binocular function and the impact of symmetry of central scotomas on these results. Methods: Thirty patients with bilateral AMD were recruited. Standard clinical tests (distance and near acuity, contrast sensitivity, stereoacuity) were performed monocularly and binocularly. Fusion at the fixation locus was tested with a computer-driven display using shutter glasses. A scanning laser ophthalmoscope was used to map the preferred retinal locus (PRL) and the retinal scotomas under monocular viewing conditions during a fixation task. An infra-red eyetracker was used to investigate gaze position changes (and indirectly retinal locus changes) during monocular versus binocular fixation of the same target. Data from both devices were combined to predict PRL position under binocular viewing. Reading speed and eye movements during reading were measured monocularly and binocularly using the eyetracker. Results: Only 17.3% of AMD patients used the same PRL to fixate in both eyes under monocular versus binocular conditions, of whom 44.5% had symmetrical scotomas and 22.3% had asymmetrical scotomas. Retinal correspondence of the PRLs was retained in 85.2% of patients. Fusion at the PRL was demonstrated for most patients with symmetrical scotomas but for the minority of patients with asymmetrical scotomas (71.4% versus 33.3%). Reading speed binocularly could be accurately predicted by the reading speed of the better eye. There was no difference in eye movements during reading between the two viewing conditions. Conclusions: Overall, there was little advantage in binocular versus monocular viewing. Patients demonstrated different PRL characteristics under these conditions and the symmetry of the retinal scotomas was the main factor to account for these differences. These results provide an insight into how people with bilateral scotomas operate in the real world. This information is essential for developing effective vision rehabilitation.