Unilateral situs inversus of optic disc associated with reduced binocularity and stereoacuity resembling monofixation syndrome

Abstract

Situs inversus of the optic disc is a rare, usually bilateral, congenital embryological abnormality associated with high myopia, optic disc coloboma or tilted optic disc. It is characterized by emergence of the retinal vessels in an anomalous direction with dysversion of the optic disc. In this report we present a 13-year-old boy diagnosed with isolated, unilateral situs inversus of the optic disc associated with reduced binocularity and stereoacuity resembling a monofixation syndrome. The clinicians should be aware of this association and assess the binocularity in patients with unilateral optic disc or macular anomalies. Conversely, patients with reduced binocularity and stereoacuity should be carefully evaluated for macular or optic nerve anomalies, if not associated with strabismus, anisometropia and eccentric fixation. Typical fundus picture, optical coherence tomography and multifocal electro retinogram of the patient would be instructive to a clinician.

Figure 1

A: 30 degree fundus photograph showing the retinal vessels emerging in nasal direction in the right eye and normal (temporal) direction in the left eye. B: OCT report of the peripapillary Fast RNFL thickness scan (3.4) showing (i) RNFL thickness in clock hour sectors, (ii) fundus image with scan circle, (iii) RNFL thickness of the quadrants and (iv) false color cross-sectional image of the retina. Note the difference in the RNFL thickness between the temporal sector and the nasal sector in the right eye (86 microns) and in the left eye (14 microns)

Figure 2

Multifocal electroretinogram (mfERG) output of the right eye showing generalized reduction in the amplitudes of the 1st order kernels. Patient's mfERG responses are on the left side and the reference values are on the right side. A) Color coded 3 dimensional topography map, B) trace arrays and C) averaged responses from the ring 1 (at fovea) to ring 6 (at peripheral macula)