Optical Gap Biomarker in Cone-Dominant Retinal Dystrophy.

PURPOSE: To characterize the progression of optical gaps and expand the known etiologies of this phenotype.

DESIGN: Retrospective cohort study.

METHODS: Thirty-six patients were selected based on the identification of an optical gap on spectral-domain optical coherence tomography (SD-OCT) from a large cohort of patients (n=746) with confirmed diagnoses of inherited retinal dystrophy. The width and height of the gaps in 70 eyes of 36 patients were measured using the caliper tool on Heidelberg Explorer by two independent graders. Measurements of outer and central retinal thickness were also evaluated and correlated with gap dimensions.

RESULTS: Longitudinal analysis confirmed the progressive nature of optical gaps in patients with Stargardt disease, achromatopsia, occult macular dystrophy, and cone dystrophies (p<0.003). Larger changes in gap width were noted in patients with Stargardt disease (78.1μm/year) and cone dystrophies (31.9μm/year) as compared to patients with achromatopsia (16.2μm/year) and occult macular dystrophy (15.4μm/year). Gap height decreased in patients with Stargardt disease (6.5μm/year) (p=0.02), but increased in patients with achromatopsia (3.3μm/year) and occult macular dystrophy (1.2μm/year). Gap height correlated with measurements of central retinal thickness at the fovea (r=0.782, p=0.00012). Interocular discordance of the gap was observed in 7 patients. Finally, a review of all currently described etiologies of optical gap was summarized.

CONCLUSION: The optical gap is a progressive phenotype seen in an increasing number of etiologies. This progressive nature suggests a use as a biomarker in the understanding of disease progression. Interocular discordance of the phenotype may be a feature of Stargardt disease and cone dystrophies.