August 24, 2012
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Visual acuity linked to subfoveal choroidal thickness in myopic eyes

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Subfoveal choroidal thickness may be a strong predictor of visual acuity in patients with myopia, according to a study.

We examined a number of parameters in highly myopic eyes without macular pathology, and among all of the measured parameters, choroidal thickness was the significant predictor of visual acuity,” corresponding author Richard F. Spaide, MD, said in an email interview with Ocular Surgery News.

Study analysis

The retrospective review analyzed 35 eyes of 25 consecutive patients in New York and 110 eyes of 61 consecutive patients in Japan. All patients had myopia of 6 D or more, and mean visual acuity was 20/25.

Optical coherence tomography images were taken of the retina and choroid. Measurements of choroidal thickness, central foveal thickness, outer retinal hyporeflective layer thickness and inner segment to retinal pigment epithelium aggregate thickness were taken from the horizontal section going directly through the center of the fovea.

Only subfoveal choroidal thickness was significantly correlated with logMAR visual acuity in both the New York patients (P = .041) and the Japanese patients (P = .001). Retinal thicknesses did not show a statistically significant correlation with visual acuity.

According to the study, a thin choroid may deliver decreased amounts of oxygen to the retina, thus potentially affecting signal generation from the photoreceptors.

More data are necessary to fully understand the relationship between the choroid and visual acuity, Spaide said, especially to determine if there is a threshold value of choroidal thickness at which visual acuity shows a significant decline.

Spaide and colleagues said further examination is needed to understand how increasing age and refraction affect choroidal thickness and choroidal blood flow to prevent visual disturbances in patients with myopia.

Impact of myopia

Myopia is a leading cause of vision impairment worldwide. According to Spaide, the number of highly myopic people is rapidly increasing, especially in East Asia.

In East Asian cultures, there are a number of factors, including large pressure to do well in school, which indirectly may influence the tendency to develop myopia,” he said.

The most important risk factors for the development of myopia include close reading and work at a young age, as well as a lack of outdoor activity.

According to Spaide, the proportion of the general population with myopia is approximately 1% to 2% in the United States, 5% to 8% in Japan and approximately 15% in Singapore.

The study, however, found no significant differences in the relationship between choroidal thickness and visual acuity attributable to clinic location or patient ethnicity. Spaide said that thus far, not much evidence exists to support myopic differences among ethnicities.

Aside from visual acuity, other visually related tasks were not examined in the study. Spaide said, for example, that a highly myopic person older than age 50 years may not feel comfortable driving at night.

Myopia, particularly high myopia, will probably grow to be the most important cause of visual loss in the world, and yet we have very little understanding of anything that is going on,” Spaide said. “There is plenty of research that needs to be done.” – by Ashley Biro 

Reference:
  • Nishida Y, Fujiwara T, Imamura Y, Lima L, Kurosaka D, Spaide R. Choroidal thickness and visual acuity in highly myopic eyes. Retina. 2012;32(7):1229-1236.
For more information:
  • Richard F. Spaide, MD, can be reached at Vitreous-Retina-Macula Consultants of New York, 460 Park Ave., Fifth Floor, New York, NY 10022; 212-861-9797, ext. 2227; fax: 212-628-0698; email: rick.spaide@gmail.com.
  • Disclosure: Spaide has no relevant financial disclosures.