A new acuity test for toddlers

Acuity measurements in adult subjects using a preferential looking test

Preferential looking (PL), as a technique for assessing visual acuity, was designed for use with young infants. There are occasions when a practitioner may need to use a PL test with an adult who is unable to participate in acuity measures with conventional optotype tests (such as an adult with learning disabilities, stroke damage or dementia). In preparation for the development of an adult-appropriate PL test, this study compared scores with the Cardiff Acuity Test (CAT, which was designed as a PL test) and a standard LogMAR-based test, the Lea chart. One hundred and one adults with learning disabilities, attending vision screening at Special Olympics, took part in acuity measures with both tests. Athletes subsequently found to have uncorrected refractive errors were excluded and analysis was confined to 72 athletes. There was no significant difference in mean acuity with the two tests, but CAT tended to overestimate scores for poorer acuities. CAT was less sensitive than the Lea chart to interocular acuity differences. Although CAT may be a successful way to assess acuity in patients unable to participate in conventional acuity tests, the practitioner should be cautious in interpreting results. There is the potential with CAT to overestimate acuity and to miss small interocular differences, so criteria for determining 'abnormality' may need to be adjusted.

Visual impairments in people with severe and profound multiple disabilities: an inventory of visual functioning

BACKGROUND

The prevalence of visual impairments in people with severe and profound multiple disabilities (SPMD) is the subject of considerable debate and is difficult to assess.

METHODS

In a typical Dutch care organization, all clients with SPMD (n = 76) participated in the study and specific instruments adapted to these clients (requiring a minimum of cooperation) were used to measure visual acuity, the visual field, binocular vision, contrast sensitivity, refractive errors and visual functioning behaviour.

RESULTS

We found an unexpected 92% of clients with SPMD to have visual impairments. Previously, only 30% were known to have visual problems. None of the persons observed had normal visual acuity. Subnormal visual acuity was the best result. The severity of the visual impairment was related to the severity of the intellectual disability. In addition to the problem of acuity, impairments in the visual field, impaired contrast sensibility and impaired binocular functioning were found, as well as impaired visual attention, fixation and following. In 22% of the clients observed, refractive errors were found and glasses were advised.

CONCLUSIONS

Consequences for caregiving and for modifications of the environment were discussed.

Problems measuring contrast sensitivity in children

A preliminary study measured the contrast sensitivity function (CSF) in 30 children (aged 3 months-5 years). Preferential looking techniques were used to assess CSF to sine wave gratings displayed on one of two screens. To find a meaningful contrast sensitivity procedure we compared the results with a shorter procedure using an edge stimulus. The following problems were encountered: measuring the contrasts required to detect four or five different spatial frequencies took time, resulting in boredom and loss of attention in our subjects; there was poor correlation between CSF and edge detection; an interesting artefact resulted in a plateau rather than a low frequency fall-off in the CSF of five of the children greater than 30 months old. This artefact may have resulted from peripheral rather than central retinal responses and/or motion artefacts in the stimulus onset. A follow up study with 41 additional children aged 3-36 months limited the contrast testing to that of the spatial frequency corresponding to the peak of the CSF. The shortened procedure, plus a lot of encouragement, resulted in higher contrast sensitivities in all but the oldest age group and successful monocular contrast measurements. In order to avoid artefacts arising from peripheral vision, children were encouraged to look at each screen before responding.