A recent study published in Annals of Clinical and Translational Neurology suggested that hypoplasia and subsequent retinal nerve fiber layer degeneration may contribute to optic nerve dysfunction in Friedreich ataxia (FA).
The researchers investigated the changes in the retinal nerve fiber layer (RNFL) in a diverse cohort of participants with FA and characterized features of vision loss to see if such changes contribute to vision loss. The team measured peripapillary RNFL thickness in 198 people with FA and 77 controls using optical coherence tomography.
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To determine the visual acuity, multiple Sloan letter charts were employed. Additionally, visual acuity and RNFL thickness data were compared to the disease severity measures, including GAA triplet repeat (GAA-TR) length, age of onset, age at data collection, modified Friedreich Ataxia Rating Scale scores, and FA Functional Disease Stage scores obtained from the Friedreich Ataxia Clinical Outcomes Measures Study.
Study results suggested that RNFLs were significantly thinner in people with FA compared to controls in all four quadrants of the retina, including temporal, inferior, superior, and nasal, in both the right eye and the left eye. Moreover, RNFL thickness variability in FRDA was best predicted by disease burden determined as the product of disease duration and GAA1. Furthermore, significant deficits in high-contrast visual acuity were observed in patients having RNFL thickness below 68 µm.
In addition, analysis of RNFL thickness based on sex showed that males had modestly but significantly thinner RNFLs than women, indicating that sex may also contribute to variability in RNFL thickness. Besides, RNFL thickness significantly predicted visual acuity in high-contrast and low-contrast visual acuity testing, indicating a strong correlation between them.
Finally, the cross-sectional analysis showed that RNFL thickness decreased with the increased disease burden, suggesting RNFL thickness decreases over time in FRDA. “More longitudinal data are needed to determine which patients will experience larger decreases in RNFL thickness over time,” the author added.
FRDA is a genetic disease with an autosomal-recessive inheritance pattern. The disease is most commonly caused by a GAA-TR expansion in intron 1 of the FXN gene. The clinical features of the disease include ataxia, cardiomyopathy, scoliosis, and diabetes which worsens over time.
Rodden LN, McIntyre K, Keita M, et al. Retinal hypoplasia and degeneration result in vision loss in Friedreich ataxia. Annals of Clinical and Translational Neurology. Published online June 19, 2023. doi:10.1002/acn3.51830