Relationship between Ocular Deviation and Visual Function in Retinitis Pigmentosa

Abstract

In retinitis pigmentosa (RP), peripheral visual-field loss starts in early stages, whereas central vision loss occurs in advanced stages. Sensory strabismus gradually occurs in RP. We investigated the relationship between ocular deviation and visual function and explored for sensory strabismus risk factors in 119 consecutive patients with RP at various stages. We assessed ocular deviation at far and near distances, that is the central visual field, using the mean deviation (MD) value and visual acuity (VA), and the residual binocular field area, using Goldmann perimetry (GP), in 33 patients. The horizontal ocular deviation at near distance was >10° in 30% patients and correlated with residual visual function. Although there was no effective cut-off value for central visual function, a cut-off residual GP area of 40 cm² distinguished patients with a larger from those with a smaller horizontal ocular deviation at far distance (P = 0.04). Our findings suggest that visual function is negatively associated with ocular deviation in patients with RP and that the sensory strabismus risk is relatively high for patients with a binocular visual field <40 cm². Thus, screening for ocular alignment may be necessary for patients with RP-associated severe vision loss as part of their comprehensive care.

Figure 1

Relationship between ocular deviation at far distance and the visual field in patients with retinitis pigmentosa. (a) The horizontal deviation at far distance (HDF) negatively correlated with the mean deviation (MD) value (P = 0.04; r = −0.20). (b) The vertical deviation at far distance (VDF) also negatively correlated with the MD value (P = 0.004, r = −0.28). There were no effective cut-off MD values for distinguishing patients with a larger ocular deviation from those with a smaller ocular deviation. (c,d) Both HDF and VDF tend to exhibit a correlation with the residual Goldmann perimetry (GP) area (P = 0.08 and 0.13, respectively). A cut-off residual GP area of 40 cm² can be set to distinguish patients with a larger deviation from those with a smaller deviation.

Figure 2

Representative colour and autofluorescence fundus photographs and optical coherence tomography (OCT) and Goldmann perimetry (GP) images for patients with retinitis pigmentosa (RP) and orthophoria or large-angle strabismus. (a–d) Representative right-eye images from a 40-year-old man with RP who exhibited a mean deviation (MD) value of −33.4 dB, residual GP area of 128.2 cm², and no horizontal or vertical deviation at far distance. (a,b) Colour and autofluorescence fundus photographs. (c) Spectral-domain OCT image. (d) GP image. (e,f) Representative right-eye images from a 52-year-old man with severe RP who exhibited an MD value of −3.4 dB, residual GP area of 28.1 cm², horizontal exodeviation of 15.4°, and vertical deviation of 1.7° at far distance. (e,f) Clour and autofluorescence fundus photography. (g) OCT image. (h) GP image. Ocular alignment is stable despite the relatively low MD value and high residual GP area. The bold lines on GP images (d,h) represent V/4e isopters.

Figure 3

Method for measuring the binocular visual field on merged Goldmann perimetry (GP) images for patients with retinitis pigmentosa. GP findings for both eyes were scanned and merged. The binocular visual field was measured and summated (right eye, red line; left eye, green line). The radius of the central 90° line (between the two arrow heads) was first set at 10.8 cm and measured on a standard recording paper. On this complex image, the residual GP area is 49.38 cm² (blue, purple, and brown areas: 3.62, 8.71, and 37.05 cm², respectively).