[Options and limits of visual function tests available on the internet].
BACKGROUND
The quantitative capability of the visual system can be tested using graphic presentations with defined size, form and colour. For presentations a chart projector or personal computer (PC) can be used. In the meantime the number of visual function tests on the internet is continually increasing. These tests are potentially available for over 400 million internet users with different hard- and software requirements.


METHODS
From 38 on-line visual acuity tests and 19 on-line colour vision tests found by means of search engines on german language web pages, the offerer of the test, the type of chart used and the data for the test conditions, as well as hard- and software adjustment were registered. RESULTS. Various visual function tests, such as visual acuity tests, the Amsler grid, stereo and colour vision tests, can already be planned via internet. The variability of the tests ranges from a simple presentation of graphic elements to a laboriously programmed interactive input by the user to specify the test result. Most of the tests are presented by opticians and the optical industry.


CONCLUSIONS
The analysed tests allow for a considerable variability of the test conditions, for example by missing data concerning the room lighting and lacking monitor calibration. Furthermore, problems of the web-based colour presentation were not considered or not considered sufficiently in most of the on-line colour tests.


CONCLUSIONS
Because of the test deficits determined, the results of visual function tests on the internet are to be classified as doubtful. At present, most data of test offerers are not sufficient with respect to the test conditions. Standards should be defined for internet-based visual function tests and further studies should be followed to check the effectiveness of these tests for screening examinations.
Kuchenbecker
J
J
Universitäts-Augenklinik Magdeburg, Germany. joern.kuchenbecker@medizin.uni-magdeburg.de
Lindner
H
H
Behrens-Baumann
W
W
D003119:Color Perception Tests; D006801:Humans; D020407:Internet; D055095:Optics and Photonics; D014787:Vision Tests; D014792:Visual Acuity