Effects of Magnifier Training: Evidence from a Camera Built in the Magnifier

Abstract

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.

Assessment of near visual acuity in 0–13 year olds with normal and low vision: a systematic review

“…A total of 12 studies were included [21–32]. Three of these studies were included for qualitative purposes [24, 25, 32].…”

“…In the 12 children with N8 or worse low vision aids were considered.Hohmann 1982 [31]Cross sectional n  = 62Group = NVAge = 6–12 yearsTest: Binocular Landolt C-testRange: 0.1–1.4 (decimal acuity)Spacing: 2.6′ and 17.2′Distance: 40 cm (and 6 m)Threshold: 88–94%Response: Verbal or matchingThe majority of subjects had vision of 1.4 (decimal).Maximum acuity uncrowded optotypes at 7 years and crowded optotypes at around 10 years.Dowdeswell 1995 [23]Cross sectional n  = 68Group = NVAge = 5;2–7;6 yearsTest: Monocular Bailey-Lovie chart at 0.3 and 6 mRange: 0.1–2.0Spacing: 1× optotype sizeDistance: 30 cm and 6 metresResponse: Not specifiedSee Fig. 3.Lovie-Kitchin 2001 [30]Cross sectional n  = 71Group = low visionAge = 7–18 yearsTest: Binocular near text visual acuity (reading test based on the Minnesota Low Vision Reading Test) and distance visual acuity (Bailey-Lovie chart)Spacing: not specifiedDistance: 10 cm and 3 metresThreshold: DVA scored per letterResponse: readingDistance vision ranged from 0.10–1.28 logMAR and near text visual acuity from 0.12–1.47 logMAR (N 1.5-N24 at 10 cm).Critical print size: 0.74–1.87 logMAR (N5-N64 at 10 cm).Labib 2009 [29]Cross sectional n  = 50Group = low visionAge = 5–15 years (mean age 11 ± 2.6 y)Test: Monocular near (Keeler’s reading chart) and distance (Landolt C)Distance: 25 cmSpacing: Not specifiedResponse: VerbalThe near visual acuities ranged from A10 to A20, with the mean near acuity ± SD being A13.632 ± 3.17171.DVA ranged from 4/60 (0.06) to 6/24 (0.25), with mean distance visual acuity ± SD being 0.12 ± 0.12.Boonstra 2012 [21]Non-randomized controlled trial n  = 21Group = low visionAge = 3 ½–6 yearsTest: Binocular LEA near chartDistance: self-chosen distance, at 40 cm and at 3 metresSpacing: 0.5 and 1.0× letter sizeResponse: VerbalSee Fig. 4.Dekker 2012 [22]Cross sectional n  = 62Group = NVAge = 4–12 yearsTest: Binocular LEA line and single at near and distanceDistance: 0.3 and 3 metresSpacing: 0.5 and 1.0× letter sizeResponse: VerbalDistance vision crowding ratio (95% CI):4–6y: 1.40 (0.88–2.22)6–12: 1.31 (0.87–1.97)Near vision crowding ratio:4–6y: 1.01 (0.55–1.86)6–12y: 1.01 (0.72–1.42)Huurneman 2012 [27]Cross sectional n  = 58/ n  = 75Group = low vision/NVAge = 4–8 yearsTest: Binocular C-test and LEA line at near/C-test at distanceDistance: 40 cm and 5 metres (if children had acuity < 20/125 distance was reduced to 2.5 metres at distance).Spacing: C-test: 2.6 and > =30; LEA line test 0.25, 0.5 and 1.0 × letter sizeThreshold: 60% (3/5)Response: VerbalSee Fig.…”

“…In three of the included papers uncrowded and crowded visual acuities were compared [21, 27, 28]. In children aged 4 to 7 years crowding, i.e.…”

“…Measuring visual acuity at a viewing distance chosen by the child can cause serious underestimations of near visual acuity in children (0.16 logMAR or 1.6 lines difference on a vision chart) [21]. An explanation for this is that under- or over accommodation of the lens can result in poorer acuities.…”

“…With the exception of one study [21], there are no other studies systematically evaluating the effect of viewing distance with the same set of subjects, and therefore comparison between studies is not possible. Differences in near vision scores of 5 year olds for crowded optotypes [21, 26, 27] suggest that the 25 cm viewing distance could result in somewhat lower acuities, but since different children were tested across studies this comparison cannot be made. Viewing distance should be controlled for and, ideally, should be fixed and at 40 cm for near visual acuity because of the influence of accommodation, and in order to allow comparisons between studies.…”