Visual function tests on the Internet--sense or nonsense?

The quantitative capability of the visual system can be tested using graphic presentations with defined size, form and color. For presentations, a chart projector or monitor can be used. Today, the number of visual function tests on the Internet is increasing constantly. Options and limitations of visual function tests using the

Internet and the authors' own test results are described.

Several visual function tests, such as visual acuity tests, the Amsler-Grid, stereo and color vision tests, can already be given via Internet. The variability of the tests ranges from the simple presentation of graphic elements to the laboriously programmed interactive input by the user to specify the test result. Under standardized examination conditions, there was a very high correspondence between the results of the authors' own web-based color vision test and those of luminescence color test plates and conventional pigment color plates.

However, the interpretation of the test results is difficult due to the absence of controls during the test as well as the heterogeneity of the hardware. In order to obtain comparable test results, differences in size and resolution as well as in brightness, contrast and color of computer monitors must be taken into consideration. Due to the deficits described in the tests, the value of visual function tests on the Internet is rather limited. Currently, the data of test distributers with respect to the test conditions are all still insufficient. Standards need to be defined for Internet-based visual function tests. However, visual function tests on the Internet can achieve test results comparable to those of conventional visual function tests under standardized examination conditions in clinical practice. Further studies are needed to check the accuracy of web-based screening examinations in ophthalmology.