Myopia severity and corneal endothelium: morphological variations across low, moderate, and high myopia

Background: Myopia, a condition of growing concern in Asian populations, has been linked to ocular structural changes that may affect corneal endothelial morphology. Endothelial cell density (ECD), shape, and size changes have been observed in cases of high myopia. However, population-specific data, particularly in Malaysia, remain limited. In this study, we evaluated corneal endothelial morphology across different severities of myopia in young Malaysian adults. Methods: For this cross-sectional study, we categorized individuals with myopia, aged 19–24 years, attending the International Islamic University Malaysia Optometry Clinic, into low, moderate, and high myopia groups, based on spherical equivalent. They underwent non-cycloplegic refraction, axial length, intraocular pressure, and slit-lamp assessments. Using a non-contact specular microscope, we measured corneal endothelial parameters, ECD (cells/mm²), coefficient of variation (CV) of the cell area, percentage of hexagonal cells (HEX, %), and central corneal thickness (CCT, micrometer) centrally, in triplicate, and averaged the values. All assessments were conducted by an experienced optometrist under controlled environmental conditions. Results: We analyzed data from 374 eyes of 187 young adults (mean [standard deviation] age: 20.16 [0.75] years) across varying degrees of myopia. Axial length increased with myopia severity, while best-corrected visual acuity remained comparable among groups. Statistically significant differences in mean ECD, CCT, and HEX (all P < 0.05), but not in CV, were observed across the three myopia groups. Post-hoc analysis revealed that, compared to low myopia, the high myopia group had significantly lower ECD, HEX, and CCT (all P < 0.05), while the moderate myopia group showed significantly reduced ECD and HEX (both P < 0.05). ECD, CCT, and HEX did not differ significantly between the moderate and high myopia groups (all P > 0.05). Conclusions: We demonstrated that higher myopia severity in young Malaysian adults was significantly associated with lower ECD, reduced HEX, and thinner CCT, whereas CV did not differ across myopia levels. These findings indicated that increasing myopia severity is associated with notable morphological changes in the corneal endothelium. Thus, progressive axial elongation in myopia may adversely impact corneal endothelial morphology and biomechanical stability. Given the cross-sectional nature and limited demographic scope of the study, further longitudinal and multi-ethnic studies are warranted to clarify the causal pathways and long-term implications of myopia-related endothelial changes.