A study of the inheritance of the central and peripheral optical properties in the human eye

Résumé

During the last three decades, a sudden outbreak of global myopia prevalence has been observed worldwide. Relative peripheral refraction has been widely discussed in recent studies in order to understand the root cause of myopia progression and its possible prevention. Recent studies found that the myopic individuals had relative hyperopic defocus in the peripheral retina, whereas emmetropic and hyperopic individuals had relative peripheral myopic defocus. This thesis was designed to investigate the variance of central and peripheral refractive error, higher-order aberrations, and biometric eye measurements in a young twin population registered with the Murcia twin registry, Spain. 100 twin pairs were included in this study with 54 monozygotic (MZ) and 46 dizygotic (DZ) twins. Manifest refraction (SE) and on-axis aberrations (LOA & HOA) were measured using a visual adaptive optics simulator (VAO, Voptica SL, Murcia, Spain). An open-view fast scanning Hartmann-Shack (HS) peripheral wavefront sensor (VPR, Voptica SL, Murcia, Spain) was used to measure the peripheral wavefront aberrations (± 35 degrees). Ocular biometric parameters were measured using Haag-Streit Lenstar LS900 (Haag-Streit AG, Köniz, Switzerland). The refraction zones were divided into three retinal areas: central measurement at line of sight (MLOS); Mid-periphery zone (Mmid-periphery) and relative periphery zone (Mrelative-periphery). The central peripheral refraction profile was further analyzed using root mean square error (RMSEPRO) and nasal-temporal asymmetry (RMSEASY). Our study subjects showed a high prevalence of myopia (77%) and the average SE was -2.0±2.0 [+3.8 to -7.0] in MZ and -2.2±2.1 D [0.0 to -9.8] in DZ twins. For manifest refraction (SE), the result showed similar intraclass correlation coefficient (ICC) values among MZ (75 %) and DZ (68 %) twin groups, suggesting a combined effect of gene and environment. The structural equation model (SEM) revealed more than half of the refraction variation at MLOS and Mmid-periphery were explained mainly by shared environmental (C) effect with only one quarter by additive genetics (A). The Mrelative-periphery showed relatively greater additive genetic control (A; 0.47) with decreased shared environmental influence (C; 0.24). The model fitting showed the relative peripheral refraction variance being explained in 0.82 by additive genetics. The peripheral image shell analysis showed relatively higher ICC among MZ twins (RMSEPRO = 68 %, RMSEASY = 65 %) than DZ (RMSEPRO = 23 %, RMSEASY = 0.16 %). The SEM showed best fitting being an AE model, describing half of the variation by additive genetics (A) and the remaining half by unique environmental influence (E). The ALLOS showed higher correlation (90 %) in MZ twins than DZ (61 %), being similar to those found off-axis (AL14 & AL20), with correlations ranging from 89 to 93 % in MZ and from 59 to 60 % in DZ twins, indicating a gene-environmental mixed influence on the variance for all the eye size traits. The biometric variance at anterior segment of the eye has shown strong genetic impact. Whereas, axial length losses its heritability by the influence of visual environmental exposures in association with axial elongation of the eye. We can conclude as the variance of manifest on-axis refraction within the study population of young twins showed a significant influence of shared environment with minimal additive genetic control. Over time, due to shared environmental influences, our study population developed a higher prevalence of myopia. However, the general trend of in the periphery didn't change with myopia development, possibly because of the lesser impact of eye growth in the periphery. The variance at the anterior segment distances of the eye showed a strong genetic impact. Whereas, the posterior ocular components losses its heritability by the influence of visual environmental exposures in association with axial elongation of the eye.