Multimodal Ophthalmic Imaging Reveals Ocular Manifestations in Spinocerebellar Ataxia Type 7

The findings from a recent case series of 3 patients with spinocerebellar ataxia type 7 (SCA7), suggests that there is limited awareness of the various ophthalmic features of the disease, but that the various ocular manifestations can be detected via multimodal imaging techniques such as spectral domain optical coherence tomography (SDOCT), which investigators noted can done rapidly and noninvasively to measure visual acuity. This in addition to a corresponding literature review of these manifestations collectively highlight the importance of multimodal imaging in the ophthalmological examination of patients with SCA7 to help with aiding in diagnosis and guiding future genetic therapies.¹

The investigators suggest that SDOCT should be routinely performed to evaluate ophthalmic disease progression over time, with other exams such as near-infrared reflectance (NIR) imaging—for photoreceptor loss and retinal pigment epithelium (RPE) disruption—and electrophysiological tests—which give essential information on cone and rod dystrophy—showing similar effectiveness for gathering a full picture of SCA7.

“SCA7 is the only spinocerebellar ataxia that seems to be associated with a decrease in visual acuity owing to retinal degeneration. In patients with SCA7, the retina develops in health before showing a progressive reduction of electroretinographic activity, retinal thinning, and silencing of genes specific to photoreceptors,” senior author Solmaz Abdolrahimzadeh, MD, PhD, associate professor of neurosciences at the University of Rome Sapienza and consultant ophthalmologist at the Azienda Ospedaliera Universitaria Sant’Andrea Rome, Italy, and colleagues wrote.¹ “SCA7, from an ophthalmological point of view, can be assessed through numerous multimodal imaging techniques to evaluate and manage the follow-up of patients.”

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In one case, a 64-year-old Congolese woman with SCA7 had a scale for assessing and rating cerebellar ataxia (SARA) score of 14, and visual assessments showed mild visual loss with pale optic discs, attenuated retinal arteries, and macular pigment mottling. SDOCT revealed central retinal thinning, outer retinal layer abnormalities, ellipsoid zone loss, and disrupted foveal photoreceptors, particularly in the right eye. Retinal nerve fiber layer and macular ganglion cell complex thinning occurred bilaterally. Despite steady central retinal thicknesses at follow-up, other structural abnormalities persisted. Visual evoked potentials were within normal limits, while electroretinography indicated reduced cone response with a slight decrease in rod response.

In the second case, a 30-year-old Israeli woman with SCA7 presented severe mobility impairment and profound visual loss. The patient showed a compromised gait, with a SARA score of 23, and extremely low visual acuity in both eyes. In ocular examinations, investigators observed limited eye motility, intense photophobia, and optic nerve pallor with peripapillary atrophy, vascular attenuation, and retinal atrophy. Using the SDOCT imaging, researchers observed a diffuse increased backscattering and significant central retinal thinning.

In the third case, a 32-year-old Italian woman with SCA7 showed red-green color blindness, retinal thinning in SDOCT, and central scotoma in visual field examinations. In the fundoscopic examination and photography, investigators observed a healthy optic nerve and slight foveal hypopigmentation. Despite this, SDOCT revealed a focal loss of the ellipsoid zone in the right eye. In addition, NIR imaging showed alterations in the RPE. Although some external layers showed a generalized granular appearance, researchers observed the retinal nerve fiber layer, optic nerve head analysis, and macular ganglion cell complex thickness remained preserved.

The literature review included 21 English studies that reported and described ophthalmologic procedures for diagnosing and following 151 patients with a known genetic mutation causing SCA7 in the MEDLINE database through August 2023. “Numerous studies present shared characteristics of best corrected visual acuity, color fundus photography (CFP), and SDOCT as the most commonly used techniques, together with some form of color vision testing and visual field examination,” Abdolrahimzadeh et al noted.¹ “Various authors reported the electrophysiological exams of patients. Less diffuse imaging techniques in the study of SCA7 are fundus autofluorescence, fluorescein angiography, and NIR. Some studies focused on specular microscopy to analyze the morphology and cell density of the corneal endothelium.”

All told, a limitation of this analysis is the few numbers of cases reported in the literature, and most articles mainly centered on neurological aspects of the disease. Therefore, the authors recommended future research on SCA7 and its ocular manifestations to confirm the proposed classifications and potential provide clinical guidelines for the approach to multimodal imaging in this disease pathology.

REFERENCES
1. Ciancimino C, Di Pippo M, Manco GA, et al. Multimodal Ophthalmic Imaging in Spinocerebellar Ataxia Type 7. Life (Basel). 2023;13(11):2169. doi:10.3390/life13112169