Effects of magnifier training: evidence from a camera built in the magnifier.

PURPOSE: This study evaluated the effect of an evidence-based magnifier training on viewing behavior in visually impaired children aged 3 to 6½ years.

METHODS: Effects of a training with a stand magnifier were evaluated by analyzing recordings of 21 visually impaired children, obtained from a miniature camera mounted in the magnifier. In a pre-test, post-test design, 11 of the children trained without magnifier and 10 children trained with magnifier. Three measures were compared from pre- to post-test assessment: 1) observation time in seconds through the magnifier during task performance; 2) the eye that was used during task performance with the magnifier (right eye/left eye as recorded by the camera); and 3) the self-chosen eye-to-chart distance (in cm) in near visual acuity measurement.

RESULTS: Three important changes were found by analyzing the eye-camera recordings: (1) There was a significant shift in average observation time (i.e., the duration of looking through the magnifier in a single glance), before and after training. In the pre-test children used less than 10 s for a glance through the magnifier, whereas in the post-test this was 10-30 s. (2) In 5 children there was no preference with respect to the number of glances through the magnifier with right or left eye during pre-test measurement. However, such a task-specific dominance was clearly observed in this subgroup after training (post-test measurement). (3) The eye-to-chart distance, as measured during near-vision testing with LH-single and LH-line test, decreased significantly over the training period (from 9.5 cm to 7.9 cm, pre- to post-test). There were no differences in the outcome measures between the with-magnifier and without-magnifier training groups. We can conclude that (1) the magnifier training had a positive effect on viewing behavior and the development of dominance, and (2) camera observations provide valuable data on children's viewing behavior.