Hyperopia Correction May Boost Accommodation, Reading Speed

Researchers have yet to fully explain the link between optical correction and accommodative response, but, new data suggests correction for pediatric patients with low to moderate hyperopia can improve their performance in near vision tasks.

The study, published in Investigative Ophthalmology & Vision Science, includes 63 healthy children between the ages of 5 and 10 years, recruited from a local school and 2 optometry clinics. Participants displayed spherical equivalent refraction in the least hyperopic eye of ≥+1.00 D to <+5 D, astigmatism of <2.00 DC, and anisometropia of <1.00 D. Two experimental conditions were designed; the first tested accommodative response during 15-minute intervals each of reading and movie viewing while uncorrected for hyperopia, and one week later, participants performed the 2 near activities with full refractive correction spectacles — after a 10-minute adaptation period.

A typical 25 cm viewing distance was used for the near tasks, and a PowerRef 3^TM (PlusOptix) infrared photorefractor simultaneously measured gaze position, pupil size, and accommodative function. The set-up was tilted downward at 16.7 degrees to simulate natural reading position. A positive treatment outcome was defined as ≥0.50 D improvement of mean accommodative accuracy with optical correction, and negative effect was described as ≥0.50 D decreased accuracy while using spectacles. The tests demonstrated that correction increased accuracy of accommodative response with significant effects of treatment outcome in both sustained activities, the active reading task (P <.001), and passive movie viewing (P <.001). Further, the effect of correction was shown throughout hyperopia values.

Regarding stability of accommodative response, microfluctuations increased while wearing eyeglasses in the reading task (P <.0001), but decreased with correction during movie viewing (P =.04). Microfluctuations may “serve as an error cue to quantify magnitude and direction of the mean defocus level to help maintain appropriate accommodative responses.” 

The study speculates that, when reading, microfluctuations increased to offer a “temporal directional sign for the accommodative controller to produce an appropriate response,” or that correction raises sensitivity of the (sensorimotor) accommodative system, stimulating error recognition, thus causing more fluctuations along with expanded accommodative response.

For reading speed, “correction significantly increased the rate of reading score” (P <.001), regardless of the amount of refractive error (P =.69). The mean improvement in reading speed with refractive correction was 3.7%±15.0%. Clinical significance is typically 5.0%.

A limitation of the study was that participants were aware when activities were uncorrected and corrected, thus the investigators suggest further study with placebo spectacles. On the other hand, this research focuses attention on the importance of testing accommodative amplitude and vergence — and visual functions with and without correction. 

Because individuals with hyperopia often display more accommodation for a target than those with myopia, eyestrain may result from interactions between accommodation and vergence. Therefore, an improvement of 0.50 D in accuracy of accommodation could turn out to be a pivotal factor when deciding whether to prescribe spectacles.

Reference

Ntodie M, Saunders KJ, Little J, et al. Correction of low-moderate hyperopia improves accommodative function for some hyperopic children during sustained near work. Invest Ophthalmol Vis Sci. 2021;62(4):6. doi:10.1167/iovs.62.4.6