Transient increase in IOP linked to subfoveal choroidal thinning, axial elongation

Key takeaways:

• A transient increase in IOP led to temporary axial length elongation and subfoveal choroidal thinning in participants with and without myopia.
• The post-IOP changes were similar regardless of refractive error.

Healthy individuals with an induced transient increase in IOP experienced temporary axial elongation and subfoveal choroidal thinning, regardless of whether they had a refractive error, according to a study in Optometry and Vision Science.

Previous research has shown that the choroid can serve as a biomarker for myopia development and progression which, in turn, is associated with increased risk for glaucoma, according to the researchers.

“Given the association between myopia and glaucoma, the effect of glaucoma and/or increased IOP on subfoveal choroidal thickness has been studied for many years, with inconsistent findings,” Hamed Niyazmand, PhD, lecturer in the division of optometry at the School of Allied Health of The University of Western Australia, and colleagues wrote.

To better understand the role of the choroid in myopia development and the relationship between posterior eye changes and myopia and glaucoma, the researchers conducted a prospective study assessing the effect of raised IOP on axial length, subfoveal choroidal thickness and central retinal thickness.

They recruited 29 healthy adults aged 21 to 26 years (mean age, 23 ± 1 years; 55% men) who were grouped into one of three categories: emmetropes (+0.50 D > spherical equivalent [SE] > -0.50 D; n = 10), low myopes (0.50 > SE > 6.00 D; n = 10) and high myopes (SE 6.00 D; n = 9).

All participants wore fitted swimming goggles for 5 minutes to increase IOP. The researchers used noncontact tonometry to measure IOP, optical biometry to measure axial length, and OCT to measure central retina thickness and subfoveal choroidal thickness at baseline, while wearing goggles, immediately after removal and 3 minutes after removal.

The groups appeared comparable in baseline IOP and central retinal thickness, the researchers reported, although high myopes had significantly greater axial length and thinner subfoveal choroidal thickness than emmetropes and low myopes.

From baseline to mid-goggle wear, the researchers observed a mean IOP increase of 1.7 ± 2.1 mm Hg (P = .002), as well as an increase in axial elongation of 14 ± 21 m (P = .012) and subfoveal choroidal thinning of 13 ± 15 m (P < .001). These changes in axial length and subfoveal choroidal thickness appeared similar across groups, and all three parameters returned to baseline after the goggles were removed.

Central retinal thickness did not change significantly between any time points or between the refractive groups.

Niyazmand and colleagues noted several limitations to this study, including their use of manual subfoveal choroidal thickness segmentation and potential inaccuracies in IOP measurements due to corneal biomechanical properties.

“Transiently increased IOP resulted in temporary axial elongation and subfoveal choroidal thinning,” the researchers wrote. “Refractive error had an insignificant influence on changes in IOP, axial length, subfoveal choroidal thickness and central retinal thickness during swimming goggle wear.

“It can be speculated that transient thinning of the choroid, associated with increased IOP, may lead to permanent choroidal thinning in the long term and make children susceptible to myopia development,” they added.

Considering that this study involved only transient changes in IOP, future studies are needed to determine the impact of prolonged IOP elevation on the aforementioned parameters and elucidate the relationship between myopia and glaucoma, the researchers wrote.

Reference:

Perspective

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Andrew Rixon, OD, FAAO

Myopia is a worldwide epidemic, with a prevalence of 5 billion expected by 2050, according to Holden and colleagues.

Multiple studies have shown an association between choroidal thinning and myopia. Relevant to glaucoma is the fact that patients with high myopia have a substantially increased risk for developing glaucoma, compounded further by the fact that confirmation of glaucoma in high myopes is often a major diagnostic challenge.

The notion that choroidal thickness, readily capturable with OCT, might have potential as a biomarker used to predict those at greater risk for myopia development, and subsequently glaucoma risk, is reasonable.

Niyazmand and colleagues sought to understand whether transiently elevating IOP in patients with emmetropia, mild and high myopia would cause thinning of the subfoveal choroid, and if so, whether that thinning would be different among the aforementioned refractive subtypes.

The researchers found that although transiently increasing IOP decreased subfoveal choroidal thickness, that thinning was not significant across the groups. They concluded that further studies are needed to understand whether subfoveal choroidal thickness is a valuable metric to unlock the association between myopia development and glaucoma. Glaucoma and high myopia remain intertwined, and, although the choroid is integral to ocular blood flow, its subfoveal thickness has not, as of yet, consistently demonstrated itself capable of becoming a biomarker clinically useful in this space.

Reference:

Holden BA, et al. Ophthalmology. 2016;doi:10.1016/j.ophtha.2016.01.006.

Andrew Rixon, OD, FAAO

Memphis VA Medical Center

Southern College of Optometry

Member, Optometric Glaucoma Society

Disclosures: Rixon reports no relevant financial disclosures.

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