Abstract
AIM: To assess the variations in photoreceptor cell packing density (PCPD) across the retina among young healthy individuals with emmetropia, low and moderate myopia. METHODS: High-resolution adaptive optics scanning laser ophthalmoscopy (AOSLO) systems were utilized for retinal imaging with a large sampling window of 700 µm×700 µm. The study cohort included 14 emmetropic [spherical equivalent (SE) ranged +0.5 to -0.5 D], 15 low myopic (SE ranged -0.5 to -3 D) and 21 moderate myopic (SE ranged -3 to -6 D) healthy young adults. Photoreceptors at 3° temporal, 6° superior and inferior 6° were captured. Statistical analysis was then performed to obtain PCPD and cell spacing. RESULTS: The average age of participants was 22.54±2.86 (ranged 20-30y) with no difference among 3 groups. At 3° temporal, the emmetropic group exhibited the highest PCPD of 15 186.16±2050.54 cells/mm(2), while the low and moderate myopic groups had PCPD of 14 009.15±1073.01 and 13 466.92±1121.71 cells/mm(2), respectively. At 3° temporal, the emmetropic group also had the smallest cell spacing at 6.66±0.26 mm, compared to 6.85±0.26 and 6.91±0.28 mm for the low and moderate myopic groups, respectively. Compared to the emmetropic group, at 3° temporal, the myopic groups showed significantly reduced PCPD (low myopia: P=0.032; moderate myopia: P=0.001). At 6° inferior, the moderate myopic group exhibited a significant decrease in PCPD (P=0.013), while at 6° superior, there were no significant statistical differences in PCPD for the low and moderate myopic groups (P>0.05). In comparison to the emmetropic group, only the moderate myopic group showed significantly increased cell spacing at all three positions (temporal 3°: P=0.011, superior 6°: P=0.046, inferior 6°: P=0.013). Correlation analysis revealed a positive correlation between PCPD and axial length changes (P<0.05). CONCLUSION: Reduced PCPD and increased cell spacing strongly correlated with refractive error in mild to moderate myopic eyes, especially at 6° inferior to the fovea and the decreased PCPD in the macular region of myopic patients may be associated with increased axial length-induced retinal stretching.