Ocular Changes Due to Spinocerebellar Ataxia

By Gregory Kosmorsky, DO, and Sruthi Arepalli, MD

Spinocerebellar ataxias (SCAs) are a group of disorders characterized by an autosomal dominant inheritance pattern, ocular motility deficits and variable neurological degenerations caused by variable unstable trinucleotide repeats. SCAs are classified by genotype with a mutation causing unstable CAG repeats in the SCA7 gene found on the short arm of chromosome 3, which codes for ataxin-7, a protein found in various cellular locations, including the retina. This leads to a pigmentary retinal degeneration caused by functional decline at both the photoreceptor and postreceptor level with equal involvement of rods and cones. Loss of retinal thickness occurs in both the foveal and parafoveal regions, with more degeneration noted centrally. Furthermore, optic nerve atrophy has been noted in individuals with the disease.

A diagnostic dilemma

These patients can pose a diagnostic dilemma for practitioners, as their ocular presentation can mimic other retinal pigmentary diseases and their optic nerve changes can mimic glaucoma. Here we present the case of a 56-year-old man with a diagnosis of SCA7 who presented for evaluation for decreased vision and who was diagnosed with pigmentary macular atrophy and glaucoma.

On initial examination, best-corrected visual acuity was 20/80 OU and intraocular pressure (IOP) was 13 mm Hg OD and 17 mm Hg OS. Extraocular movements were full, and pupils were equal and reactive to light with no afferent pupillary defect.

Anterior segment examination was significant for 1+ nuclear sclerotic cataract OU. Dilated fundus examination revealed enlarged cups OU (0.75 OD and 0.85 OS), with inferior temporal thinning OD and inferior thinning OS, confirmed on optic nerve optical coherence tomography (OCT). Macular OCT showed inner and outer segment loss and atrophy OU. Fundus autofluorescence showed posterior pole hyperfluorescence with significant atrophy in the fovea. Humphrey visual fields showed decreased foveal sensitivity OU, with the left eye greater than the right. We observed scattered and central defects in the right eye and a shallow superior arcuate angle in the left. Since the patient had a family history of spinocerebellar ataxia-7, the pigmentary retinopathy was attributed to this diagnosis.

However, given the potentially glaucomatous changes in his optic nerves, the patient was started on latanoprost, then eventually switched to brimonidine, then timolol-dorzolamide, given limited IOP response to these medications and progressive thinning seen on optic nerve OCT.

Two years after presentation, the patient developed optic nerve pallor OU, prompting an evaluation with neuro-ophthalmology to assess whether these changes were related to his systemic neurological condition rather than glaucoma.

Given his history of SCA7, we felt that these ocular changes were in fact due to the SCA7 disease. The patient was kept on his glaucoma medications to minimize any possible damage from glaucoma, although we suspected the majority of his pathology was from SCA7. At his last outpatient follow-up, his vision was stable at 20/80 OU.

A team approach

Working together, our Cole Eye Institute team of neuro-ophthalmology, glaucoma and pediatric glaucoma subspecialists was able to diagnose this patient’s disease. Initially, it was thought that his optic nerve changes were due to glaucoma. However, with further inquisition, it became apparent that these changes were from SCA7.

Working closely with Cleveland Clinic’s Genomic Medicine Institute, Cole Eye Institute has the ability to diagnose and treat rare genetic disorders.

Disc photograph of the right eye of a patient who presented with abnormal disc thinning.

Disc photograph of the right eye three years after presentation with abnormal thinning and pallor, inconsistent with glaucoma, which prompted evaluation for neuro-ophthalmological causes of the disc changes.

Dr. Kosmorsky is a neuro-ophthalmology specialist. Dr. Arepalli is an ophthalmology resident.