Ocular Component Growth From the Cornea to the Sclera in Non-Human Primate Emmetropization

To quantify ocular parameters and their relationships during normal ocular development in rhesus monkeys.

This retrospective analysis included rhesus monkeys with a normal visual experience and no experimental interventions (N = 210). Retinoscopy, biometry (Lenstar), optical coherence tomography (OCT; SPECTRALIS), and tonometry were performed in both eyes at age 24 ± 2 days. Twelve monkeys were followed longitudinally up to age 362 days. OCT scans were analyzed for retinal, choroidal, and scleral thickness. Data were analyzed using t-tests and linear mixed-effects models to assess sex and age effects. Associations between parameters were examined.

At baseline, there were no significant interocular differences in spherical equivalent refraction (P = 0.30) or axial length (P = 0.98). Females weighed less than males and exhibited thinner central corneas, greater corneal powers, shallower anterior chamber depths, thinner lenses, and shorter axial lengths (P < 0.05 for all). Longitudinal analyses showed that spherical equivalent refraction became less hyperopic with age, but axial length and retinal, choroidal, and scleral thickness increased in a non-linear manner. Choroidal and scleral thickness showed significant variability across monkeys with modest correlation coefficients.

This study established normative in vivo trajectories of ocular parameters, including retinal, choroidal, and scleral thickness, during early development. Rhesus monkeys were initially hyperopic and underwent coordinated refractive and structural changes consistent with early emmetropization. Refraction, axial length, and retinal thickness followed expected patterns, but choroidal and scleral thickness exhibited substantial variability and only modest associations with age.