Structural and Functional Retinal Changes in Achromatopsia

Achromatopsia is a rare, hereditary retinal disease that reduces the quality of life by causing low vision and photophobia and has no definitive treatment yet. This study aimed to detect the structural and functional changes seen in the retinas of cases diagnosed clinically with achromatopsia (ACHM) who applied to a tertiary care center, which is the only low vision center in our country. In this prospective, cross-sectional clinical study, 62 eyes of 31 cases with achromatopsia who applied to Ankara University Faculty of Medicine, Department of Ophthalmology, Vision Research, and Low Vision Rehabilitation Unit between July 2022 and August 2023 were examined. In statistical analysis, the data of the better seeing eye were compared. Eye examination and color vision examination, macular pigment optical density (MPOD) measurements, and microperimetry tests were performed on the cases. Retinal changes were divided into 5 stages according to the ellipsoid zone by optical coherence tomography (OCT). They were combined into two groups as follows: those with an ellipsoid zone (stages 1 and 2) and those without an ellipsoid zone (stage 3, stage 4, and stage 5) for the statistical analysis. All cases had photophobia, 22 (71%) had nystagmus, and 5 (16%) had strabismus. The average number of defined color plates was found to be 1.97±1.92 plates. Considering well-seeing eyes, the mean best-corrected visual acuity (BCVA) was 0.85±0.18 logMAR. The fundus was normal in 42% of the eyes, retinal pigment epithelium (RPE) irregularity was present in 48%, and RPE atrophy was present in 10%. The mean MPOD was 1.32±2.27 dB, and retinal sensitivity was 20.85±4.61 dB. It was observed that the fixation was unstable in 83% of the cases, and central fixation was only present in only 8% (46%was placed on the nasal side of the fovea). The mean central macular thickness (CMT) was 124.88±59.15 microns. The stages of the changes in the macula were as follows: 28% of the eyes were stage 1, 13% were stage 2, 14% were stage 3, 19% were stage 4, and 26% were stage 5. It was observed that 41% of the eyes had an ellipsoid zone, and 59% did not. Foveal hypoplasia was present in 52% of the eyes, 25% was grade 1, 14% was grade 3, 18% was grade 4, and hypoplasia was atypical in 43%. It was observed that 56.5% of the macula had hypoautofluorescence, 22% was normal, 13% had hyperautofluorescence, and 8.5% had no autofluorescence. There was no correlation between mean retinal sensitivity values and OCT findings with BCVA. However, a significant relationship was detected between the presence of the ellipsoid zone and age, CCT, and FAF pattern. As age increased, the number of cases without an ellipsoid zone increased (p=0.044). While the ellipsoid zone was observed in 62% of the cases aged 15 and under, it decreased to 21% in cases aged 15 and over. CCT was thicker in cases with an ellipsoid zone (p=0.005). A relationship was found between cases without an ellipsoid zone and hypo-autofluorescence (p<0.001). It was observed that the MPOD measurement results of the cases were lower than normal data, and there was no significant relationship between MPOD and age, gender, nystagmus, iris color, smoking, nutritional status, BCVA, number of defined color plates, BCEA 63%, average retinal sensitivity, contrast sensitivity, fundus findings, OCT findings, and FAF pattern. It has been suggested that the structure and function of photoreceptors in the macula are more important than age in determining the appropriate candidate to benefit from gene therapies in achromatopsia. In our study, structural and functional changes that can be seen in the retina were detected in this disease group, which has limited information in the literature since it is sporadic. It was thought that although the changes in the retina were progressive with age, they appeared to be stable in terms of BCVA. However, it was concluded that long-term, large number of cases and longitudinal studies are needed. Keywords: Achromatopsia, Photophobia, Gene therapy, Macular pigment, Retina