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Ditta Zobor, Franco Stanzial, Ulrich Kellner, Günther Rudolph, Bernd Wissinger, Susanne Kohl, Eberhart Zrenner; Retinal structure and function in Achromatopsia: the CNGA3 phenotype. Invest. Ophthalmol. Vis. Sci. 2014;55(13):346.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate retinal function, and to characterize the retinal changes in patients with achromatopsia (ACHM) due to mutations in the CNGA3 gene by using spectral-domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF)
ACHM patients with known mutations in the CNGA3 gene were examined. A complete ophthalmological examination was performed by the same investigator in every patient including psychophysical tests (ETDRS visual acuity, color vision tests, visual field, microperimetry and dark adaptation thresholds) and extended electrophysiology (Ganzfeld and multifocal ERG). The appearance and thickness of all retinal layers were evaluated by SD-OCT and FAF.
Thirty patients (mean age 33.7 years, range: 7 to 56 years) were included. Mean BCVA was 20/140 in the complete forms (cACHM, 28 cases) and 20/60 in the incomplete cases (iACHM, 2 cases). The Rayleigh anomaloscope matches were consistent with a rod-dominated function in every cACHM patient. Microperimetry indicated an overall lower retinal sensitivity within 20° of visual field. In the electrophysiological examinations, photopic responses were non-detectable in cACHM patients, but residual cone responses could be observed in the iACHM patients. ISCEV rod threshold amplitudes and implicit times were within normal limits, while Vmax was significantly below normal values (p<0.05). In contrast, slope (n) and semisaturation intensity (k) were found to be within normal limits. On the morphological level, SD-OCT examination showed no specific changes in 22.2%, IS disruption at the fovea in 36.2%, absent IS in 22.2%, an “intraretinal bubble“ in 13.8% and outer retinal atrophy including RPE loss was seen in 5.6% of all cases. Foveal hypoplasia was found in 21 patients (70%), but surprisingly, no correlation with BCVA could be observed. The severity of morphological and functional changes lacked a robust association with age. A specific correlation to the genotype could not be observed.
Thirty CNGA3-related ACHM patients were examined with identical functional and morphological methods. In preparation to a therapeutic gene therapy trial, high-resolution techniques were used to assess photoreceptor structure and function in patients with ACHM. These findings will be useful for the identification of patients concerning future therapeutic trials. The data imply that the therapeutic window seems to be wider than previously indicated.
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