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A.R. Watts, A. Jain, J. Giles, C. Korulla, R.M. Bhola; Computer Modelling of the Use of Hardy–Rand–Rittler Pseudoisochromatic Plates as a Measure of Color Desaturation in Optic Neuropathy . Invest. Ophthalmol. Vis. Sci. 2005;46(13):647.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To model the use of Hardy–Rand–Rittler (HRR) pseudoisochromatic plates to quantify optic nerve dysfunction. HRR plates may be used to quantify color desaturation due to optic neuropathy. However, these plates were designed for inherited color blindness, and may not be suited to measure acquired neurological color loss. We investigated this test's usefulness in red, blue or combined color desaturation using a computer model. Methods: The 24 HRR plates were scanned into a PC, and were manipulated using Corel Photo–Paint 8 imaging software, to desaturate each image from 100% color to 0% in 10% steps. This was done for the master saturation channel, then for the red and blue channels individually. The manipulated images represent what an observer would see if their color vision was desaturated by that amount, for example by an optic neuropathy. In 10 normal volunteers, we assessed the level of desaturation at which each subject could correctly identify each plate, and the results for all 10 subjects were amalgamated together, to calculate the mode % desaturation at which each plate was recognised. Graphs were produced of the HRR score (out of 24) which one would expect for each 10% loss of color saturation in the red, blue and master channel. Results: For master color desaturation, the graph showed a relatively straight oblique line from 0% desaturation (normal vision) down to 70%, but at this point the HRR score reached a plateau, and stayed at 3/24 as the desaturation increased to 100%. For red desaturation, the graph showed that the HRR score remained normal until the red vision had been impaired by 50%, and then decreased in a linear fashion until the red vision was 80% desaturated, at which point it again plateaued at 14/24. For blue desaturation, the graph showed a linear decline from 30% down to 100% desaturated for blue. Conclusions: HRR plates do show some relation to % color loss, but this is far from linear, and for red and blue, the plates would not pick up color desaturation until it had reached at least 30%. For combined color desaturation the situation is reversed, with the test picking up color desaturation as small as 10%, but failing to detect deterioration beyond the 70% level, potentially giving false reassurance that vision is not deteriorating further. Other tests of color vision may be more reliable for diagnosing and monitoring color desaturation in optic nerve disease.
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