Cone photoreceptor density in the Copenhagen Child Cohort at age 16-17 years

To examine cone density in relation to gestational and morphological parameters in the Copenhagen Child Cohort (CCC2000).

The macula was imaged using adaptive optics in 1,296 adolescents aged 16-17 years. Axial length and distance visual acuity were determined. Absolute and angular cone photoreceptor density were analysed for an 80 × 80-pixel area, 2 degrees temporal to the fovea. Association with axial length was analysed with linear regression. Correlation with visual acuity was described with a Pearson correlation coefficient. Associations of cone density with gestational parameters, maternal smoking, sex and age were analysed using multiple regression adjusted for axial length.

Mean absolute cone density was 30,007 cones/mm² (SD ± 3,802) and mean angular cone density was 2,383 cones/deg² (SD ± 231). Peri- and postnatal parameters, sex and age had no statistically significant effect on cone density (p > 0.05). Absolute cone density decreased with longer axial length (-2,855 cones/mm² per mm or -9.7% per mm, p < 0.0001). For angular density, which included a correction for the geometrical enlargement of the eye with axial length, a decrease with axial length was detectable, but it was small (-20 cones/deg² per mm or -0.84% per mm, p = 0.009).

The decrease in cone density per unit solid angle with increasing axial length was small, less than 1 percent per mm, indicating that expansion of the posterior pole during the development of refraction takes place without a clinically significant loss of cones. Perinatal parameters, within the spectrum presented by the study population, had no detectable effect on cone density.