For each unit increase in myopia, the risk of glaucoma increases by approximately 20%, finds AJO study

Glaucoma is the leading cause of irreversible blindness worldwide, and OAG is the most prevalent form of glaucoma. A well-established risk factor for OAG is myopia, the association between them having been thoroughly investigated. The evidence on the association of myopia degree with increased risk of OAG, however, is contradictory. According to some studies, an association exists between myopia of any degree and OAG, whereas other investigations have reported links only with high myopia.

Clearer understanding of the myopia/OAG-risk association calls for wider and deeper investigation, particularly given its significant public health urgency. Ahnul Ha et al extended the scope of Marcus et al. in quantity and quality and updated the pool of selected studies in seeking to identify a dose-response relationship between myopia degree and OAG risk.

Authors searched the PubMed, EMBASE, and Cochrane databases for population-based studies published until 30 November 2020 and reporting on both myopia and OAG.

• Twenty-four (24) studies in 11 countries (514,265 individuals) made up the meta-analyses. The pooled OR of any myopia degree's association with OAG was 1.88 (95% CI, 1.66–2.13; I2 =53%).

• The OR differences based on ethnicity (Asians vs. Westerners) or 5 geographic areas were not statistically significant (P=0.80 and 0.06, respectively).

• The pooled ORs of the associations between low, moderate, moderate-to-high, high myopia, and OAG were 1.50 (95% CI, 1.29–1.76), 1.69 (1.33–2.15), 2.27 (1.74–2.96), and 4.14 (2.57–6.69), respectively.

• According to the DRMA, the pooled OR (per SE 1 D change) was 1.21 (95% CI, 1.15–1.28); the OAG risk accelerated at around –6 D, and further accelerated from –8 D, showing a nonlinear concave upward slope (P=0.03).

The meta-analysis suggested that myopia sufferers have a roughly doubled risk of developing OAG compared with those without myopia. Additionally, the DRMA represented the relationship of myopia with OAG risk as a concave upward slope, the risk accelerating from –6 D and further accelerating from –8 D.

Authors found that the odds of developing OAG increased gradually from 1.504 to 4.142 with the increase of the degree of myopia from low to high. This pronounced dose response relationship seems to suggest a possible explanation for the pathogenesis of glaucomatous damage in eyes with myopia. Because of myopic eyes' elongated AXL and thinner sclera, the ONH has been presumed to be more vulnerable to the damage typically incurred in glaucoma. Additionally to the mechanical susceptibility perspective, vascular theory postulates that a contributory factor to glaucomatous optic neuropathy is insufficient ocular perfusion. Atrophy of the retinal pigment epithelium and choroid in myopic eyes, furthermore, may diminish retinal cells' access to essential molecules along with their ability to handle oxidative stress. These changes progress with myopia's course, possibly contributing to development of glaucomatous injury.

"In conclusion, every myopia category, including low, moderate, moderate-to-high, and high, was significantly and dose-dependently associated with increased risk of glaucoma. Notably, our results suggest a non-linear relationship between them, showing a steeper glaucoma-risk increase in higher-degree myopia. From a public health perspective, both myopia and glaucoma are among the most prevalent and rapidly increasing eye diseases causing vision impairment and blindness globally. There should be increased awareness of glaucoma among individuals with myopia, regardless of its degree. Importantly, more vigilant monitoring is needed in myopia worse than –6 D, given the steeply increasing risk incurred in high-degree myopia."

Source: Ahnul Ha , Chung Young Kim , Sung Ryul Shim MPH , In Boem Chang MD , Young Kook Kim , Degree of Myopia and Glaucoma Risk: A Dose-Response Meta-Analysis, American Journal of Ophthalmology (2021)

doi: https://doi.org/10.1016/j.ajo.2021.10.007