Clinical studies on straylight and glare

L.J. van Rijn1, C. Nischler2, D. Gamer3, L. Franssen4, G.C. de Wit4, J.E. Coppens4, R. Kaper1, D. Vonhof1, G. Grabner2, H. Wilhelm3, H.J. Völker-Dieben1 and T.J.T.P. van den Berg4.

1 Department of Ophthalmology, Vrije Universiteit Medical Center, Amsterdam, the Netherlands,
2 Landesklinik für Augenheilkunde und Optometrie,
Salzburg, Austria,
3 Universitäts-Augenklinik, Tübingen, Germany and
4 The Netherlands Ophthalmic Research Institute, Amsterdam, The Netherlands

Address for correspondence: Dr. L.J. van Rijn, ophthalmologist EBOD, Vrije Universiteit Medical Center, PO Box 7057, NL-1007 MB Amsterdam, The Netherlands

This is a short summary of a part of the study. For the full study report, please contact Dr. G.C. de Wit at the Netherlands Ophthalmic Research Institute, Meibergdreef 47, NL-1105 BA Amsterdam, The Netherlands.

Introduction
Measurement of glare and straylight can potentially provide useful information
about the visual capacity of elderly drivers and drivers with blurring of the eyelens (cataract). However, the widespread implementation of such measurements critically depends on the availability of a proven measurement technique for glare that is reproducible, valid and resistant to fraud. Moreover, this technique has to be able to discriminate between ‘normal’ and ‘impaired’ subjects and provide information about visual capacity that is not provided by visual acuity alone. The measurement techniques that are currently available, have been insufficiently investigated, regarding these aspects.

Purpose
The purpose of the current study was to evaluate the properties of several test
devices for measurement of glare and straylight: the Nyktotest and Mesotest as well as the Straylight meter. A new version of the straylight meter, that has been developed to facilitate large-scale implementation and improve fraud-resistance, was also included in the study.

Methods
Three groups of subjects were studied: 1) Young subjects without any eye disease; 2) Elderly subjects without any eye disease and 3) Subjects with (early) cataract in at least one eye. All subjects underwent a battery of glare and straylight tests, as well as measurement of visual acuity, contrast sensitivity, refraction, eye colour and objective assessment of cataract. (LOCS III classification). Subjects filled up a questionnaire into perceive disability during driving.

Results

1. Repeatability.
In relation to the range of obtained measurement outcomes, repeatability is about similar for all tests. However, when repeatability is considered in relation to the difference between ‘normal’ values and the cut-off criterion, then the New straylight meter is superior to the remaining tests.

2. Validity.
The relation between the outcomes of glare and straylight tests and the amount of cataract (blurring of the lens, expressed in the LOCS III lens classification) and the results of a questionnaire into perceived disabilities during driving was studied. The results indicate that the relations to LOCS III and questionnaire are strongest for the Conventional and New straylight meters. However, as yet there is no objective quantification of driving difficulties in relation to glare and straylight available. Therefore our conclusions regarding validity are confined to relations between the various tests.

3. Discriminative ability The ability of each test to discriminate between the three groups (young/elderly/cataract) was studied. Both straylight meters were superior on this aspect. These tests hardly revealed any false positives (elderly and young subjects who failed the tests).

4. Resistance to fraud The New straylight meter has a better resistance to fraud than the conventional one.

5. Added value of the test. Furthermore, it was investigated whether the tests provided extra information about group assignment (young/elderly/cataract) surpassing the information provided by visual acuity and contrast sensitivity. The added value was found to be largest for the New straylight meter. Conversely, visual acuity provided the least extra information in presence of New straylight meter results, less so than in presence of the results of the remaining glare/straylight tests. This indicates that the New straylight meter provided the best information about group assignment of the subjects.

Conclusions
Of the glare/straylight tests that were investigated, the New straylight meter was
superior. Repeatability, discriminative ability, resistance to fraud and added value were all on the level that should be required from a test. Further studies, focussing on validity and prevalence of impairments, should reveal whether implementation of this test for the assessment of drivers is waranted.

Acknowlegdement
This study was supported by Grant ITREN E3/2000/7/SI2.282826 of the European Union.