Intra-ocular shape asymmetry in myopic Chinese eyes

Purpose: To investigate inter-ocular and intra-ocular shape asymmetries in Chinese and Caucasian individuals with both myopia and emmetropia.Methods: Thirty-seven myopes (anisometropia of less than 0.5D) and fourteen emmetropes aged 19 to 30 years were assessed. Refractive error was measured using the Nidek Tonoref II (Birmingham Optical Group, Birmingham, UK) and the mean spherical equivalent (MSE) calculated. Axial length (AL) and peripheral ocular length (PL) at 20 degrees in superior, nasal, inferior, and temporal locations were obtained using the IOL Master (Carl Zeiss Meditec, Oberkochen, Germany). Relative peripheral ocular length (RPL) was calculated by subtracting AL from the PL and was used to determine posterior globe shape. Central (CCT) and peripheral corneal thickness (PCT) up to 5 mm from the corneal apex, anterior chamber depth (ACD), and corneal curvature (CC) were measured using the Pentacam (Oculus, Wetzlar, Germany). The ocular biometric data were compared between the two eyes across all study subjects to analyse inter- and intra-ocular shape asymmetry.Results: The mean MSE was -3.36±2.29D RE and -3.29±2.12DLE for the Chinese myopes (n=20) and -2.59±1.33D RE and-2.75±1.61D LE for the Caucasian myopes (n=17). Mean AL in the Chinese myopes (RE 24.84±1.32mm, LE 24.79±1.28mm) was not significantly (p>0.05) different from the Caucasian myopes(RE 24.85±1.02mm, LE 24.88±1.04mm). No significant interocular differences were found in all groups. Nasal-temporal and superior-inferior asymmetries were found in the Chinese myopic eyes with greater retinal expansion in the nasal (-0.43 ± 0.28mm(P= 0.02)) and superior (-0.18 ± 0.37mm (P=0.01)) quadrants. Nointra-eye peripheral length asymmetry was found in the emmetropic or Caucasian myopic groups. No significant inter-eye asymmetry in CCT, PCT, ACD, and CC was found (P>0.05), but intra-ocular analysis found nasal-temporal asymmetry of PCT in all refractive groups (P<0.05)