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H. Jungnickel, K. Strohm, M. Gebhardt, H.-J. Grein; Evaluation of a Modified Siemens Star for Accurate Measuring of Contrast Sensitivity. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2534.
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© ARVO (1962-2015); The Authors (2016-present)
To enable subjective measuring of the relative low visual improvements through higher order aberrations correction, particularly sensitive and accurate visual tests are essential. Conventional contrast sensitivity tests on charts are unsuitable for that purpose. Up to now Siemens stars are used to check optical systems. Aim of the study was to develop a new contrast test using a sinusoidal Siemens star as test pattern.
Test patterns (programmed with Flash, Adobe Systems) were presented on a standard 15" TFT display. Peripheral parts of the pattern (= low spatial frequencies) can be resolved whereas central parts (= high spatial frequencies) are seen as a uniformly grey area. Subjects interactively change the size of a black circle almost stepless via PC keyboard to mark the threshold of resolution. In a pilot study with 10 subjects measurements with 5 different contrasts (20%, 10%, 5%, 2.5% and 1.25%) were performed with 10 repeats for each contrast. Siemens star either was stagnant or rotated with 10 degrees per second to prevent local adaptation. The Flash program calculated mean detectable spatial frequency in each case. Test distance was 6 meters (20 feet), one eye was occluded.
On average the adjusted spatial frequencies were 37.1 cycles per degree (at a contrast of 20%), 31.6 cpd (10%), 26.2 cpd (5%), 21.1 cpd (2.5%) and 15.9 cpd (1.25%). No significant differences between stagnant and rotating Siemens stars were found. Standard deviations for sets of 10 repeats rise with decrease of contrast and average between ±12.4% and ±26.2%. Reducing repeats down to 5 also produces precise results.
The modified Siemens star seems to be an adequate test for quick and accurate determination of contrast sensitivity. Low standard deviations show a good applicability to verify improvements of correcting higher order aberrations.
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