A new statistical case history analysis in the American Journal of Ophthalmology demonstrates an interesting dose-response relation between myopia and open-angle glaucoma.
There’s a whole new reason to get that myopia corrected, and it’s far more important than making a fashion statement with your fancy new specs. A new study by Ha et al., entitled Degree of Myopia and Glaucoma Risk: A Dose-Response Meta-analysis, reinforces the long-held belief that myopia, or nearsightedness, is strongly correlated with the development of open-angle glaucoma (OAG), the world’s leading cause of blindness worldwide.*
This double-whammy link between OAG and myopia is not particularly great news at a time when myopia rates around the world are marching upward. The authors estimate that by 2050, worldwide numbers of myopia and high myopia will have skyrocketed to nearly 5 billion and 1 billion people, respectively.
Unfortunately, the bad news doesn’t stop there — we’re still aboard the train to frown town. The study also purports to demonstrate a long-suspected and oft-debated link between higher degrees of myopia and increased risk of developing OAG that should open the eyes of glaucoma researchers everywhere.
New Tricks for Old Data Dogs
For the paper, the authors mined the PubMed, EMBASE, and Cochrane library for studies that were published before November 30, 2020. The records encompassed 514,265 individual cases of comorbid myopia and OAG across 24 studies in 11 countries.
A 2-stage dose-response meta-analysis was applied to the raw data. If fancy statistics-talk is not your forte, this is a method commonly used to measure the effects of pharmaceuticals at different dosages. In this case, the level of myopia (per spherical equivalent decrease of 1 diopter) was inputted as the “dosage” and the risk of glaucoma in that group was the “effect.” The final confidence interval (CI) was 95%. For the uninitiated, this means the authors are more than pretty sure they are onto something here.
Curves in All the Wrong Places
And what they seem to be onto is big news, but in an “uh-oh” kind of way. The first piece of information the authors share is a rather old hat to those in the know, but scary nonetheless: Individuals with myopia carry twice the risk of those without myopia in developing OAG.
After identifying this positive correlation between myopia and OAG in their data, the study’s authors applied the dose-response meta-analysis, and what they found was stunning. For each 1 diopter (D) increase in myopia, the risk of developing open-angle glaucoma increased by a whopping 20 percent.
It gets worse for myopia sufferers. The grim reality is that the dose-response correlation between open-angle glaucoma and myopia is not linear, but rather curved in a concave upward slope.
Specifically, Ha et al., found that starting at -6 D, the risk of developing open-angle glaucoma begins to accelerate until hitting -8D when it starts to further accelerate. From 0 to -6 D spherical equivalent, the odds ratio increased from 1 to just under 2. However, from -6 to -8 D, the odds ratio increases from around 2 to just over 5 at -8 D. Though data was scant for myopia over -8 D, the data plotted shows an even more extreme increase in odds ratio from -8 D onwards.*
A Possible Culprit
So what’s behind this trend? Unlike other previous studies that this analysis built on, the investigators in this one had a fresh piece of information — that dastardly curve accelerating risk from -6 D. This novel insight led the study authors to a new hypothesis about the link between myopia and OAG.
The pathogenesis of glaucomatous damage in myopic eyes might be due to optic nerve head (ONH), according to the study’s authors. In myopic eyes, AXL (axial length) is elongated and the sclera thinner, the ONH might be more vulnerable to glaucoma damage. As the degree of myopia increases, ONH alterations spread beyond the optic disc shape and parapapillary gamma zone. The study authors postulate that these changes to the ONH’s biomechanisms might be behind this connection.
From a vascular perspective, the neuropathy in glaucoma has also often been thought to be from insufficient ocular perfusion, further providing credence to this theory. And finally, atrophy of the retinal pigment epithelium and choroid that mark myopia may make it difficult for retinal cells to be properly nourished — another potential piece of the puzzle behind this link.*
A New Reason to Get Tough with Myopia
The study’s authors may have cracked a part of the code in discovering the secrets behind glaucoma’s pathogenesis. But ultimately, OAG might actually turn out to be just the beginning of serious eye disease whose risk positively correlates with myopia. Macular degeneration, retinal detachment and cataract joins the rogue’s gallery of potentially devastating consequences associated with nearsightedness.1 So for those with refractive errors lucky enough to have access to eye care, there’s a whole new reason to keep those trips to the eye doctor regular — it might just save your sight.
*Ha A, Kim CY, Shim SR, Chang IB, Kim YK. Degree of Myopia and Glaucoma Risk: A Dose-Response Meta-analysis. Am J Ophthalmol. 2022; 236:107-119.