Torsional anomalous retinal correspondence effectively expands the visual field in hemianopia

Abstract

Purpose: Exotropia in congenital homonymous hemianopia has been reported to provide field expansion that is more useful when accompanied with harmonious anomalous retinal correspondence (HARC). Torsional strabismus with HARC provides a similar functional advantage. In a subject with hemianopia demonstrating a field expansion consistent with torsion, we documented torsional strabismus and torsional HARC.

Methods: Monocular visual fields under binocular fixation conditions were plotted using a custom dichoptic visual field perimeter. The dichoptic visual field was also modified to measure perceived visual directions under dissociated and associated conditions across the central 50° diameter field. The field expansion and retinal correspondence of a subject with torsional strabismus (along with exotropia and right hypertropia) with congenital homonymous hemianopia was compared with that of another exotropic subject with acquired homonymous hemianopia without torsion and to a control subject with minimal phoria. Torsional rotations of the eyes were calculated from fundus photographs and perimetry.

Results: Torsional anomalous retinal correspondence documented in the subject with congenital homonymous hemianopia provided a functional binocular field expansion up to 18°. Normal retinal correspondence was mapped for the full 50° visual field in the control subject and for the seeing field of the acquired homonymous hemianopia subject, limiting the functional field expansion benefit.

Conclusions: Torsional strabismus with anomalous retinal correspondence, when occurring with homonymous hemianopia provides useful field expansion in the lower and upper fields. Dichoptic perimetry permits documentation of ocular alignment (lateral, vertical, and torsional) and perceived visual direction under binocular and monocular viewing conditions. Evaluating patients with congenital or early strabismus for HARC is useful when considering surgical correction, particularly in the presence of congenital homonymous hemianopia.

Figure A1

Monocular Goldmann visual fields were measured on two separate days show excellent repeatability (as in Fig. 5, left eye field is plotted on the right). Superior position of the left eye physiological blind spot in the left eye field indicates intorsion (target V4e for (a) and III4e for (b)). The expected rotation of the vertical meridian based on retinal photo torsion is marked by the tilted dashed lines. Additional residual visual fields in left (inferiorly) and right eye (superiorly) are highlighted in green (b). These could be due to spared/misdirected nerve fibers from the blinded hemi retina that ended in the spared hemisphere. Such crossing over is not rare but is rarely possible to notice except in cases of hemianopia.

Figure 1

Schematic binocular (dichoptic) visual field diagrams in right homonymous hemianopia illustrating the (a) Binocular field in orthotropia (both eyes fixating). (b) Binocular field in right exotropia (left eye fixating). (c) Binocular field in left esotropia (right eye fixating). Field expansion is evident to the right of the vertical midline in the cases of lateral strabismus (b & c). However, with strabismus, the areas seen by both eyes (white) are diplopic, unless harmonious anomalous retinal correspondence (HARC) is developed.

Figure 2

Schematic binocular visual field diagrams illustrating the visual field expansion in right homonymous hemianopia with torsional strabismus. Field expansion is evident to the right of the vertical midline. Areas seen by both eyes (white) are diplopic unless HARC is developed. (a) Intorsion, the superior field expansion is from left eye and the inferior field expansion is from the right eye (b) Right exotropia with intorsion (left eye fixating) (c) Left esotropia with intorsion (right eye fixating). The field expansion is illustrated by the areas seen by either eye to the right of the vertical midline.

Figure 3

(a) Left eye fundus with optic disc margin and blood vessels traced. Foveal and optic disc centers are marked and used in calculations. (b) Estimated normal position of the optic disc (dashed ellipse) center relative to the fovea is calculated from the known anatomical relationship. Angle of intorsion (12.7°) is measured between from observed (solid ellipse) and estimated positions of the optic disc.

Figure 4

Subject maintained fixation on the projected central fixation cross inside a frame. Under subject’s instruction the filled square target was moved to align it to the center of the open frame under dichoptic viewing conditions. Retinal correspondence was thus measured using alignment of non-fusible peripheral targets.

Figure 5

Fundus photos for each eye and the corresponding monocular Goldmann visual fields are shown. Retinal areas corresponding to the hemianopic field are shown in lower contrast. Superior position of the left eye’s physiological blind spot in the left eye field indicates intorsion. The dashed lines in corresponding retina and field diagrams are rotated by the amount measured from the retinal images.

Figure 6

Binocular Goldmann visual field plots (left) and Dichoptic Visual Field (DVF) plots (right) are shown for Subject 1. DVF fields are restricted by the goggles to only 60°. DVF plots were mapped under binocular viewing condition (central binocular fixation) while presenting monocular targets. Monocular targets detected by the right eye are shown as filled red triangles pointing to right and those detected by the left eye are shown as open blue triangles pointing to left. Rotation of the vertical meridian due to measured intorsion (from Nidek images) are marked by the dashed lines (red and blue) for right and left eye, respectively. The apparent restricted nasal fields are artifacts due to the mismatch between the subjects’ and the goggles’ pupillary distances.

Figure 7

Binocular Goldmann visual field plots (left) and Dichoptic Visual Field (DVF) plots (right) are shown for Subject 2. Figure follows the same conventions as Figure 6.

Figure 8

Binocular Goldmann visual field plots (left) and Dichoptic Visual Field (DVF) plots (right) are shown for Subject 3. Figure follows the same conventions as Figure 6.

Figure 9

Measurement of retinal correspondence with the DVF for each subject (Subject 1-top row, Subject 2-middle row and Subject 3-bottom row). Primary deviation (left panel): sighting dominant eye fixates (left eye for Subject 1 and right eye for Subjects 2 and 3) and the non-dominant eye sees filled square targets to be aligned with the center of the open frame seen by the fixating eye. Secondary deviation (middle panel): non-dominant eye now fixates (right eye for Subject 1 and left eye for Subjects 2 and 3) and the dominant eye sees the square targets to be aligned with the center of the open frame now seen by the non-dominant eye. Binocular fixation (right panel): fixation target, square target and the open frame (marked in the figure) were seen binocularly.3-sided frames are used in the figure to aid in eye identification.