Three groups of patients, namely, patients with POAG with high myopia (POAG-HM group), patients with POAG without high myopia (POAG group), and patients with high myopia without glaucoma (HM group) who were matched for age, sex, and best-corrected visual acuity (BCVA), were enrolled in this study. All patients with glaucoma were recruited from the Glaucoma Clinic of the Eye and ENT Hospital of Fudan University (Shanghai, China). Patients with high myopia without glaucoma were recruited from the Refractive Clinic of the same hospital. The study adhered to the tenets of the Declaration of Helsinki, and all procedures were approved by the human subjects’ review committee of the Eye and ENT Hospital of Fudan University. All participants provided written informed consent before the procedures.
The diagnosis of POAG was based on the presence of glaucomatous optic neuropathy (GON) and a history of elevated intraocular pressure (IOP; ≥ 21 mmHg). GON was identified based on any of the following signs: optic nerve rim thinning, notching, excavation, RNFL defects, or asymmetry in the vertical cup/disc ratio of ≥ 0.2 between the two eyes. GON was independently assessed by two glaucoma specialists, and inconsistencies between the two specialists were adjudicated by a third glaucoma specialist. Patients were excluded from the study if they had pathologic myopia, media opacities, any other ocular disease, history of ocular surgery or laser, and systemic diseases, or were using medications that might induce optic neuropathy. If both eyes in an individual patient satisfied the inclusion criteria, one eye was randomly included in the study. The axial length (AL) of all patients was > 26 mm, and the BCVA was ≥ 20/25. During the data collection period, the IOPs of patients with glaucoma were all controlled at < 21 mmHg by using antiglaucoma drugs. High myopia was defined as a refractive error < -6.0D.
All subjects underwent comprehensive ophthalmologic examinations: BCVA, applanation tonometry, digital fundus photography, and Intraocular Lens Master measurement (Carl Zeiss, Jena, Germany). All patients with glaucoma underwent Humphrey perimetry with the 10 − 2 and 30 − 2 Swedish interactive thresholding algorithms. Reliable visual field results were defined as ≤ 33% false positives, false negatives, reliable factor ≤ 15%, and pupil diameter ≥ 3 mm. The total and quadrant mean sensitivity (MS), mean deviation (MD), and pattern standard deviation (PSD) in both 30 − 2 and 10 − 2 algorithms were included in subsequent analyses.
All subjects also underwent OCT (Cirrus HD-OCT) data collection. Peripapillary scans were performed on each eye to measure RNFL thickness, and macular scans were performed to measure macular GCIPL thickness. The GCIPL scan summed the thicknesses of the ganglion cell layer and the inner plexiform layer, which represent the ganglion cell bodies and the ganglion cell dendrites, respectively. Only scans with a signal strength of ≥ 6 and no motion artifacts were kept for analysis. The parameters obtained from the RNFL scans included the average, sector (superior, nasal, inferior, and temporal), and symmetry thicknesses. The parameters obtained from the GCIPL scan included the average, minimum, and sector (superotemporal, superior, superonasal, inferonasal, inferior, and inferotemporal) thicknesses.
According to the structure–function maps developed by Garway-Heath et al.13 and Kanamori et al.,14 the 10 − 2 VF test points were divided into four sectors topographically corresponding to GCIPL sectors, and the 52 test points of the 30 − 2 VF algorithm were divided into four sectors corresponding to RNFL sectors. Based on previous studies,15 the retinal sensitivities of each VF test point expressed in decibels were first converted to apostilbs, averaged for each sector, and converted back to decibels.
Age, refractive error, BCVA, IOP, AL, cup/disc ratio, OCT parameters, and perimetric parameters were compared among the three groups using one-way analysis of variance (ANOVA) followed by Bonferroni post hoc test to detect between-group differences. Spearman’s rank correlation coefficient (r) was used to determine correlations between OCT and Humphrey perimetric parameters. We assessed concordance between the OCT and perimetric parameters by using the cross-classification method based on quartiles. Agreement was defined as having the same or adjacent quartiles, and disagreement as a difference in one quartile. Extreme disagreement was defined as a difference in two or more quartiles. The level of agreement between the two methods was analyzed using weighted κ statistics. Weighted κ is defined as the percent agreement, adjusted for chance, and allows for different levels of agreement. A weighted κ of 1 represents perfect agreement, so values close to 1 indicate high levels of agreement. κ values of ≥ 0.75, 0.4–0.75, and < 0.4 were defined as high, moderate, and low agreement, respectively. A P value < 0.05 indicates that the agreement between the two methods was statistically significant.