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Study finds inverse correlation between IOP, myopia progression
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A 2-year study conducted on a large population of 12-year-old Chinese schoolchildren showed an inverse correlation between myopia progression and IOP.
The study retrospectively analyzed the data of the Anyang Childhood Eye Study , a prospective study on myopia development in Chinese schoolchildren, who were measured for cycloplegic refraction, axial length and IOP. A total of 1,558 children who completed the follow-up were included in the analysis.
Over 2 years, a mean change of spherical equivalent of -1.05 D was reported. Myopic children progressing by more than 1.0 D had a mean IOP of 15.94 mm Hg, while those progressing by less than 1.0 D had mean IOP of 16.42 mm Hg.
“That is, the mean IOP was lower in faster progressing eyes,” the authors noted.
The study was meant to explore a possible correlation between higher IOP and myopia development but, surprisingly, found that the opposite was true: Myopia progression was correlated with significantly lower IOP.
“Thus, our hypothesis is that IOP is not a casual factor for myopia progression in children, but that lower pressure in progressing myopic eyes is a direct consequence of their higher scleral compliance,” the authors wrote.
This hypothesis is substantiated by previous experiments in animal models, showing that myopia development in mammals is related to experimentally induced increased distensibility of the posterior sclera. According to the authors, it is possible that myopic children, who progress more rapidly during school years due to environmental pressure, have a greater scleral compliance than their emmetropic peers.
“Further research is needed in this area, because low scleral compliance could be a predictor of myopia progression,” they concluded. – by Michela Cimberle
Disclosure: None of the authors reported a relevant financial disclosure.
Perspective
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Derek MacDonald, OD, FAAO
In adults, myopia is both a risk factor and a confounding comorbidity in the diagnosis of glaucoma. Specific to the former, myopic eyes tend to have higher IOPs and poor biomechanical support for the retinal ganglion cells at the lamina (clinically presenting as lower corneal hysteresis), contributing to an increased prevalence of open-angle glaucoma in a dose-response fashion.
In infants, the sclera lacks the cross-linking that strengthens the adult sclera, resulting in increased compliance: an extreme sequela is buphthalmos, distention of the ocular coats due to the significantly elevated IOP of congenital glaucoma. It stands to reason that the biomechanically weaker globes of nonglaucomatous children may experience more moderate IOP-mediated axial elongation, leading to increased myopia in another dose-response relationship.
To their surprise, Li and colleagues found the opposite: IOP was significantly lower in eyes with progressive myopia. They hypothesize that eyes destined to become myopic demonstrate extreme scleral compliance, elongating at relatively low IOPs (which, akin to the underestimation of IOP with thin central corneal thickness, may not be as low as we think). I’m left curious whether measurement of corneal hysteresis may help clarify the relative risk of developing both myopia in childhood and glaucoma in adulthood.
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