High Myopia Reduces Choroidal Thickness, Axial Length, Diurnal Variation

Choroidal thickness (ChT) distribution varies based on quadrant and eccentricity according, to a study in Clinical Ophthalmology.

Researchers examined the distribution of ChT and the diurnal variation in ChT and axial length (AL) spanning a wide range of myopic refractive error in 34 adults between the ages of 18 and 35 years. Participant groups included patients with emmetropia, myopia, and high myopia. Researchers evaluated ChT in macular (foveal, parafovea, perifovea) and peripheral regions (6mm from foveal pit) in 4 quadrants (superior, temporal, inferior, and nasal). They also included measurements of ChT and AL taken at 8 AM, 12 PM and 4 PM to assess diurnal variation.

Investigators found that ChT thins progressively towards the periphery, with the superior and nasal quadrants exhibiting the thickest (277±73µm) and thinnest (218±89 µm) choroid, respectively. The team observed thinner choroids (237±48 µm) in the high myopia group, compared with the myopia group  (264±78 µm, P <.05). Patients with high myopia exhibited a significant choroidal thinning in all quadrants except for the temporal (all P <.05), and both ChT and AL underwent a significant diurnal variation (P <.05). The ChT and AL diurnal variation amplitudes in the high myopia group  were significantly reduced (ChT: 14.6±11, AL: 14.5±13 µm) compared with the emmetropia group (ChT: 21.4±15, AL: 21.3±8.5 µm) and myope groups (ChT: 19±17, AL: 19±9.7µm). There was no significant difference in diurnal variation amplitude in ChT across quadrants and choroidal eccentricity regions (P >.05). 

“The findings of significantly reduced variation amplitude in high myopes were limited in the central choroid,” according to researchers. “[This] may suggest that the central choroid had a greater contribution to active choroidal changes related to myopia development compared to the peripheral region.”

Study limitations include possible confounding due  to a participant pool consisting of a majority of women, and the inability to take measurements outside of certain hours.

Reference

Alanazi M, Caroline P, Alshamrani A, Alanazi T, Liu M. Regional distribution of choroidal thickness and diurnal variation in choroidal thickness and axial length in young adults. Clin Ophthalmol. 2021;15:4573-4584. doi:10.2147/OPTH.S334619