Abstract
Purpose: :
Anatomic torsion and sensory adaptation is common in early onset vertical strabismus. Anomalous Retinal Correspondence (ARC) in patients with congenital homonymous hemianopia is reported in 6 cases in the literature. These patients exhibit exotropia on the side of the blind field that serves to expand their visual field (panoramic vision). Using dichoptic field mapping and Nidek MP-1 fundus photo we report the first case of torsional ARC in a 44 year-old male with congenital right homonymous hemianopia as well as right exotropia (RXT) and hypertropia (RHT).
Methods: :
A custom developed computerized Dichoptic Visual Field (DVF) system that uses DLP projector and Ferro-electric LC shutter goggles was used. Retinal correspondence was mapped for the central 25º radius visual field. The DVF system can present fixation target (FT), peripheral targets (T) and a background image (BG) monocularly, binocularly, or in any desired combination. This permits mapping correspondence under different conditions. We mapped correspondence in 5 conditions (primary deviation: OS fixates, secondary deviation: OD fixates, and 3 Binocular conditions: FT to OU with peripheral targets shown either to OD, OS or OU). A 1.2º cross centered in a 3º square was used as a FT. A gray background with a 3º peripheral stationary open square (SS) was used as a BG. The same eye(s) always viewed FT and BG. The patient was instructed to look at the center cross all the time. A filled square (1.2º) was moved slowly until it was reported by the patient to be centered within the SS. 11 positions of SS was tested. MP-1 fundus photo was analyzed for angle of torsion.
Results: :
Cover test showed RXT of 6 Δ for far and 12 Δ at near along with 10 Δ RHT for both far and near. Prism neutralization of lateral tropia resulted in uncrossed diplopia suggesting ARC. Patient also showed anatomic intorsion (OD: 18º and OS: 13º) measured from fundus photos and monocular visual fields and did not report any diplopia. Binocular visual field showed expansion consistent with the torsion, larger in the inferior field, in addition to 10º lateral expansion centrally from RXT. Harmonious ARC was found with the Bagolini striated glasses and in all the tested locations of the 5 test conditions.
Conclusions: :
Panoramic vision provided by exotropia on the side of the blind field is beneficial for obstacle detection. An associated Harmonious ARC eliminates diplopia and also provides veridical perceived visual direction in the expanded field. Our patient additionally had torsional strabismus (OD) that provided greater field expansion inferiorly, that is more useful for mobility.
Keywords: strabismus • visual fields • binocular vision/stereopsis