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.

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.

Eccentric gaze direction in patients with central field loss.

PURPOSE: This study describes the binocular eccentric gaze direction (EGD) of 434 patients with binocular central field loss and presents a comparison with other studies on eccentric gaze behavior. METHODS: We reviewed the records of 434 patients with bilateral central scotomas. Eligible patients had not received eccentric viewing training and demonstrated a spontaneously developed eccentric gaze behavior. Data were collected on monocular and binocular EGD, visual acuity, and underlying ocular pathology. Findings concerning the EGD were compared with other studies that evaluated gaze behavior in patients with central field loss. RESULTS: In the group of 434 patients, age-related macular disease was the most frequent pathology (77%). The majority of these patients demonstrated a binocular EGD (bEGD) to the right (50%). In 25% of the patients, a superior bEGD was found. Less often, a bEGD to the left (14%) and to inferior (11%) were encountered. Review of the literature indicates that the majority of patients developed a monocular EGD in the superior direction. CONCLUSIONS: This is a study on bEGD behavior in a large population of patients with bilateral central scotomas. The bEGD was guided by the gaze of the better-seeing eye. The preference for a bEGD to the right differs from findings of previous studies. Review of the literature suggests that not only the ocular pathology but also the method of investigation is most likely to influence the observed EGD. Most studies evaluated the location of the preferred retinal locus using a monocular technique; this may not reflect an individual's actual binocular behavior as it relates to activities of daily living.

Young children's use of a visual aid: an experimental study of the effectiveness of training.

We report an experiment concerning the use of a stand magnifier by young children with visual impairments (21 males, 12 females; mean age 4y 8mo [SD 11mo]). Children had a normative developmental level and a visual acuity of 0.4 or less (< or =20/50 in Snellen's notation). To measure magnifier use objectively, we developed a task that closely resembled the dynamics of its real-life (pre-reading) use. Children had to follow trails visually, from a start location to an unseen end location. This could only be done successfully and reliably by proper use of the magnifier. In addition to this, we analyzed the effect of specific training with the magnifier by using a repeated-measures (before and after training) matched-groups (with respect to age and near-visual acuity) design. Results established both the task's efficacy as an instrument for measuring magnifier use in young children and the effectiveness of the training. Improvement in task performance after training was found in both groups, except for the youngest children (<3y 6mo). On average, 1.8 times as many paths were followed in both groups after training (p=0.001). The without-magnifier training group became 2.5 times as good at finding the correct end location, whereas the with-magnifier training group became 4.3 times as good (p=0.05).

Long-term evaluation of eccentric viewing spectacles in patients with bilateral central scotomas.

PURPOSE: Yoked prism spectacles (eccentric viewing spectacles [EVS]) facilitate eccentric viewing in patients with bilateral central scotomas. This study was conducted to evaluate the long-term success and patient satisfaction of this type of low-vision aid. METHODS. In this retrospective cross-sectional study, we reviewed the low-vision rehabilitation records of all patients who received EVS since 1993. With an 18-item survey, 191 patients were questioned about the wearing characteristics, advantages, and disadvantages of the EVS. Descriptive and nonparametric statistics were applied to compare regular users with those persons who no longer use the EVS. RESULTS: The response rate was 83.2% and the average follow-up time was 4.5 years. Forty percent of all patients still used the EVS. The main disadvantages of these spectacles, mentioned mainly by the nonusers, included the heavy weight (41%), perception of curved lines (46%), dizziness during walking (46%), and poor cosmetic appearance (25%). Many successful long-term users considered the EVS suitable for home activities (86%) and walking in the street (70%) and reported that this device reduced eccentric viewing (77%), created better vision in the center of their visual field (67%), and helped with recognition of objects and faces (64%). CONCLUSIONS: The prescription of EVS aids eccentric viewing in patients with dense central scotomas. Although associated with a number of disadvantages and side effects, 40% of the patients continued to use EVS. The results of this study indicate that patients who experience difficulties with eccentric fixation are most likely to benefit from these low-vision aids. A thorough explanation of the advantages and disadvantages of the EVS is important to prevent unnecessary disappointments.