Date Published: January 23, 2017
Publisher: Public Library of Science
Author(s): Yu Sawada, Masanori Hangai, Makoto Ishikawa, Takeshi Yoshitomi, Sanjoy Bhattacharya.
The influence of myopia on glaucoma progression remains unknown, possibly because of the multifactorial nature of glaucoma and difficulty in assessing a solo contribution of myopia. The purpose of this study is to investigate the association of myopia with visual field (VF) progression in glaucoma using a paired-eye design to minimize the influence of confounding systemic factors that are diverse among individuals.
This retrospective study evaluated 144 eyes of 72 subjects with open-angle glaucoma, with similar intra-ocular pressure between paired eyes, spherical equivalent (SE) ≤ -2 diopter (D), and axial length ≥ 24 mm. Paired eyes with faster and slower VF progression were grouped separately, according to the global VF progression rate assessed by automated pointwise linear regression analysis. The SE, axial length, tilt ratio and torsion angle of optic discs, Bruch’s membrane (BM) opening area, and gamma zone parapapillary atrophy (PPA) width were compared between the two groups. Factors associated with faster VF progression were determined by logistic regression analysis.
The mean follow-up duration was 8.9 ± 4.4 years. The mean value of SE and axial length were -6.31 ± 1.88 D and 26.05 ± 1.12 mm, respectively. The mean global visual field progression rate was -0.32 ± 0.38 dB/y. Tilt ratio, BM opening area, and gamma zone PPA width were significantly greater in the eyes with faster VF progression than those with slower progression. In multivariate analysis, these factors were significantly associated with faster VF progression (all P < 0.05), while SE and axial length were not associated with it. In myopic glaucoma subjects, tilt of the optic disc and temporal shifting and enlargement of the BM opening were associated with faster rate of VF progression between paired eyes. This suggests that myopia influences VF progression in glaucomatous eyes via optic disc deformations rather than via refractive error itself.
The association of myopia with glaucoma is a focus of interest in the field of glaucoma. Previous studies have reported a high incidence of myopia in patients with glaucoma [1, 2]. A systematic review and meta-analysis of 13 studies, including 11 population-based studies, reported that the odds ratios of association between myopia and glaucoma were 1.88 for any myopic condition and 1.77 for low myopia (up to -3 diopter [D] in spherical equivalent [SE]) . The authors concluded that myopia was a risk factor for the development of glaucoma. Despite its evident association with the development of glaucoma, the association of myopia with the progression of glaucoma remains controversial. Chihara et al. reported that severe myopia was a risk factor for visual field (VF) progression in patients with open-angle glaucoma (OAG) . However, several other studies were unable to establish similar association [4–8]. An evidence-based review of 85 articles reporting risk factors for glaucomatous VF progression found myopia to be an unlikely risk factor .
This retrospective study was approved by the institutional review and ethics boards of the Akita University Graduate School of Medicine, Akita, Japan, and followed the tenets of the Declaration of Helsinki. Participants did not provide written or vertical consent owing to the retrospective nature of this study.
Among the 146 subjects with 292 eyes that were initially screened, we excluded the following (some for multiple reasons): difference in IOP between paired eyes > 1mmHg in NTG, or > 2 mmHg in POAG (n = 68); difference in CCT between paired eyes > 10μm (n = 10); OCT images of poor quality (n = 7); unreliable VF test results (n = 7); congenital optic nerve abnormalities (n = 3); and epiretinal membrane (n = 2). The remaining 144 eyes (72 subjects) were included in the analysis. The subjects included in the present study were all Japanese. Among included, 18 eyes of 10 subjects were pseudophakic. The ICCs for the measurement of tilt ratio, torsion angle, and BM opening area were 0.94 (95% CI, 0.91–0.97), 0.93 (95% CI, 0.90–0.96), and 0.96 (95% CI, 0.93–0.98), respectively.
As far as we are aware, this study is the first to evaluate the association of myopia with VF progression in OAG eyes using a paired-eye study design to eliminate the effect of systemic factors that vary among individuals. In addition, we ensured that the IOP and CCT between paired eyes were similar, in order to minimize their effects on VF progression. In these study settings, as consistent with the results of previous studies, we found no association between myopic refractive errors and VF progression. However, we found that disc tilt accompanying temporal shifting and enlargement of BM opening was independently associated with faster VF progression. This suggests that myopia influences glaucomatous VF progression not via refractive error or axial length itself, but via myopic optic disc deformation.
Our paired-eye study demonstrated significant association between glaucomatous VF progression and myopic optic disc deformation such as disc tilt and temporal shifting and enlargement of the BM opening. These results suggest that myopia influences glaucomatous VF progression via optic disc deformations. In the management of patients with OAG with myopia, fellow eyes with greater optic disc deformations should be considered to be at a greater risk for faster VF progression.