The relationship between axial length and choroidal thickness in eyes with high myopia

To investigate the choroidal thickness in highly myopic eyes with no history of choroidal neovascularization or ocular surgery, and to correlate it with axial length, age, and spherical equivalent.

Retrospective, comparative, noninterventional case series.

A total of 120 eyes of 83 patients with high myopia (spherical equivalent ≥-6 diopters or axial length ≥26 mm) and 96 eyes of 62 healthy patients were studied in a clinical setting. Eyes with prior vitreoretinal surgery or laser or anti-vascular endothelial growth factor therapy were excluded. Eyes were imaged using optical coherence tomography employing a 6-mm line, reference position "Choroid," and image averaging 50. Choroidal thickness was manually measured from the posterior edge of the retinal pigment epithelium to the choroid-scleral junction at 500-μm intervals up to 2500 μm nasal and temporal to the fovea. Statistical analysis was performed.

The high myopia group mean age was 54.4 ± 18.2 years (range, 18-99) and mean axial length was 29.17 ± 2.44 mm (range, 26.00-35.63). Mean macular choroidal thickness was 115.5 ± 85.3 μm (range, 6.9-436.0). The choroid was thickest temporally (134 μm), then subfoveally (130 μm), and was thinnest in the nasal area (68 μm). This pattern differed markedly from the control eyes. In the high myopia group, axial length had the best correlation with choroidal thickness (r = -0.740; P < .001). Choroidal thickness decreased 25.9 ± 2.1 μm for each additional millimeter.

Axial length is especially associated with choroidal thickness in high myopia. Choroidal thickness profile in highly myopic patients differs from that in emmetropic patients.