The Near Triad and Accommodation Accuracy in Emmetropic and Myopic Children.

Abstract

Abstract: : Purpose: Inaccuracies of the accommodation and convergence responses have been linked to myopia development and progression. The near pupillary response, which has received little attention so far, may also be associated with myopia. The primary purpose of this study was to clarify the link between the near triad (accommodation, vergence and pupillary response) and myopia development and progression. In addition, accommodation inaccuracies at distance were investigated by measuring NITM (nearwork–induced transient myopia). Methods: Thirty–eight children (28 emmetropes: mean Rx=+0.48±0.36D and 10 myopes: mean Rx=–2.20±1.76D) aged 5–11 years participated in the study. Accommodation responses, pupil sizes and convergence were measured using a PowerRefractor. Continuous data were taken under naturalistic conditions while children read for 5 minutes an age–appropriate text at 33 cms wearing their habitual refractive correction. Distance (4 m) measurements were taken for 1 minute before and 2 minutes after the near task. Results: Near accommodation lags were increased in myopes (mean=1.42±0.59D) compared to emmetropes (mean=0.58±0.48D) (p<0.01) in accordance with previous literature. No significant differences were found between refractive groups in the pupillary responses (mm of constriction per diopter of accommodation), which significantly increased with age only in the myopic group (r²=0.36). Similarly, no refractive group differences were found in the pupillary constriction (from 4 m to 33 cms), which increased significantly with age in both refractive groups (p<0.01). Changes in vergence were not significantly different between refractive groups. However, increased convergence per diopter of accommodation was found in myopes (p<0.01). Following the 5 minutes of reading, myopic children showed increased NITM values (mean=–0.15±0.05D) compared to emmetropes (mean=–0.05±0.04D); this difference approached significance (p=0.06). Preliminary longitudinal data suggest that increased NITM values and near lags occur during the progression phase of myopia. Conclusions: Differences in the near triad between emmetropic and myopic children appear to be due to differences in the accommodation response, with pupillary and vergence responses playing a minor role.

Keywords: myopia • reading • refractive error development