Crowded task performance in visually impaired children: magnifier versus large print.

BACKGROUND

This study compares the influence of two different types of magnification (magnifier versus large print) on crowded near vision task performance.

METHODS

Fifty-eight visually impaired children aged 4-8 years participated. Participants were divided in two groups, matched on age and near visual acuity (NVA): [1] the magnifier group (4-6 year olds [n = 13] and 7-8 year olds [n = 19]), and [2] the large print group (4-6 year olds [n = 12] and 7-8 year olds [n = 14]). At baseline, single and crowded Landolt C acuity were measured at 40 cm without magnification. Crowded near vision was measured again with magnification. A 90 mm diameter dome magnifier was chosen to avoid measuring the confounding effect of navigational skills. The magnifier provided 1.7× magnification and the large print provided 1.8× magnification. Performance measures: [1] NVA without magnification at 40 cm, [2] near vision with magnification, and [3] response time. Working distance was monitored.

RESULTS

There was no difference in performance between the two types of magnification for the 4-6 year olds and the 7-8 year olds (p's = .291 and .246, respectively). Average NVA in the 4-6 year old group was 0.95 logMAR without and 0.42 logMAR with magnification (p < .001). Average NVA in the 7-8 year was 0.71 logMAR without and 0.01 logMAR with magnification (p < .001). Stronger crowding effects predicted larger improvements of near vision with magnification (p = .021).

CONCLUSIONS

A magnifier is equally effective as large print in improving the performance of young children with a range of visual acuities on a crowded near vision task. Visually impaired children with stronger crowding effects showed larger improvements when working with magnification.