Evaluation of the Choroidal Thickness Using High Penetration Optical Coherence Tomography With Long Wavelength in Highly Myopic Normal Tension Glaucoma

Abstract

Purpose: : To evaluate the choroidal thickness measured by high penetration optical coherence tomography (HP-OCT) using long wavelength (1060nm) in highly-myopic normal tension glaucoma (NTG) and compared with normal subjects.

Methods: : Twelve eyes of 8 patients diagnosed as NTG under 45 years old (yo), who had intraocular pressure (IOP) under 21mmHg, spherical equivalent refractive error (SERE) between -6 and -12 diopter (D) and axial length (AL) over 26.5mm, were enrolled in glaucoma clinic and high myopia clinic of Osaka University Hospital. The choroidal thickness in these eyes and 12 eyes of age-, refractive error-, and axial length-matched healthy was measured using the prototype HP-OCT (Swept-source, 50,000 A-scan/sec) at the fovea and 5 locations (2mm superior, temporal, inferior to the center of the optic nerve head (ONH) and 2mm superior (supero-temporal), inferior (infero-temporal) to the temporal). The data was compared and analyzed by statistical analysis software (JMP 8.0, SAS Institute).

Results: : Mean age (33.4 vs. 31.2yo, P=0.3), IOP (13.7 vs. 14.2mmHg, P=0.6), SERE (-9.3 vs. -8.8D, P=0.3), and AL (27.6 vs. 27.2, P=0.08) were similar between highly myopic NTG group and control group. Mean choroidal thickness in highly myopic NTG group and control group was (166 vs.276 microns, P<0.001) at the fovea, (172 vs. 241microns, P<0.05) at the superior, (161 vs.244microns, P<0.01) at the supero-temporal, (110 vs.161microns, P<0.01) at the temporal, (111 vs. 159microns, P<0.05) at the infero-temporal, (123 vs.162microns, P=0.051) at the inferior around the ONH. Stepwise analysis indicated that highly myopic NTG correlated significantly with the foveal choroidal thickness (P < 0.0002, R²=0.4). The area under the receiver operator characteristic (ROC) curve for the foveal choroidal thickness was 0.88, and the cutoff value determined by ROC curve was 227 micron.

Conclusions: : Choroidal thickness in highly myopic NTG is significantly thinner at the superior, supero-temporal, temporal, infero-temporal around the optic disc, and at the fovea than in normal highly myopic eyes. Choroidal thinning is somehow related with highly myopic NTG by way of choroidal circulatory disturbance or ocular growth.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • choroid • myopia