High myopia worsens eyesight

Visual acuity (VA) and contrast sensitivity (CS) appear to be impaired in people with high myopia, according to a recent Singapore study.

“[H]igher degrees of myopia and longer axial length (AL) are associated with reduced visual performance,” researchers said. “The data of this study may be particularly relevant to populations with a high prevalence of myopia and in jobs with high visual requirements.”

Researchers performed a cross-sectional analysis of 148 emmetropes (mean age, 21.52±1.05 years) and 564 high myopias (mean age, 20.95±1.17 years). All participants were male. The mean spherical equivalents (SE) of the respective groups were 0.10±0.23 D and –8.76±2.04 D. The corresponding mean ALs were 23.69±0.62 mm and 27.31±1.13 mm. [Int Ophthalmol 2020;doi:10.1007/s10792-020-01403-7]

High myopias were then divided into three: group 1 (SE from –6 to > –8 D; n=221), group 2 (SE from –8 to > –10 D; n=201) and group 3 (SE ≤ –10 D; n=142).

Increasing myopia correlated with worse visual performance. Superior corrected distance VA (CDVA), for example, was most prevalent in group 1, as was superior CS. Under photopic conditions, CDVA was measured using the high-contrast logMAR vision chart. Under mesopic conditions, the Rabin Super Vision Test was used.

A multiple logistic regression model further confirmed that drops in photopic and mesopic CDVA and CS were common in myopia groups. Relative to emmetrope controls, poor photopic CDVA was significantly more likely to occur in groups 1 (odds ratio [OR], 6.389, 95 percent confidence interval [CI], 3.051–13.378), 2 (OR, 11.399, 95 percent CI, 5.454–23.825) and 3 (OR, 27.250, 95 percent CI, 12.569–59.078).

The same was true for poor mesopic CDVA (group 1: OR, 8.854, 95 percent CI, 4.907–15.975; group 2: OR, 14.131, 95 percent CI, 7.736–25.813; group 3: OR, 28.890, 95 percent CI, 14.767–56.518). Impaired mesopic CS was also significantly more common in the high myopia groups than in the emmetrope controls.

A separate regression model showed that axial length was likewise significantly correlated with reductions in photopic CDVA (OR, 1.468, 95 percent CI, 1.320–1.632), mesopic CDVA (OR, 1.571, 95 percent CI, 1.419–1.738) and mesopic CS (OR, 1.516, 95 percent CI, 1.375–1.672).

“This study demonstrates the association between refractive error with reduced CDVA and CS in a large population with high myopia,” the researchers said. “The results of this study may be of particular interest in populations with a high prevalence of myopia, especially among Asians.”

“Several hypotheses may explain the suboptimal visual performance in myopic eyes despite full refractive correction,” they added. These include pathological myopia, lower quality of myopic eyes, optical factors of myopia-correcting lenses and lower neural sampling in myopic eyes.

There is also evidence that “other mechanisms are involved” in the observed discrepancy in visual performance, the researchers continued. Future efforts are needed to more definitively outline these underlying processes.