Color space distortions in patients with type 2 diabetes mellitus CLAUDIA FEITOSA-SANTANA, 1,2 NESTOR N. OIWA, 1,3 GALINA V. PARAMEI, 4 DAVID BIMLER, 5 MARCELO F. COSTA, 1,2 MARCOS LAGO, 1,2 MAURO NISHI, 6 and DORA F. VENTURA 1,2 1 Depto. Psicologia Experimental, Instituto de Psicologia, Universidade de São Paulo, São Paulo, Brasil 2 Núcleo de Neurociências e Comportamento, Universidade de São Paulo, São Paulo, Brasil 3 Depto. F ísica Geral, Instituto de F ísica, Universidade de São Paulo, São Paulo, Brasil 4 Institute of Psychology, Darmstadt University of Technology, Darmstadt, Germany 5 Department of Health and Human Development, Massey University, Palmerston North, New Zealand 6 Hospital Universitário, Universidade de São Paulo, São Paulo, Brasil (Received September 5, 2005; Accepted May 4, 2006! Abstract Color vision impairment was examined in patients with type 2 diabetes mellitus ~ DM2! without retinopathy. We assessed the type and degree of distortions of individual color spaces. DM2 patients ~n = 32!, and age-matched controls ~ n = 20! were tested using the Farnsworth D-15 and the Lanthony D-15d tests. In addition, subsets of caps from both tests were employed in a triadic procedure ~ Bimler & Kirkland, 2004!. Matrices of inter-cap subjective dissimilarities were estimated from each subject’s “odd-one-out” choices, and processed using non-metric multidimensional scaling. Two-dimensional color spaces, individual and group ~ DM2 patients; controls!, were reconstructed, with the axes interpreted as the R 0 G and B0 Y perceptual opponent systems. Compared to controls, patient results were not significant for the D-15 and D-15d. In contrast, in the triadic procedure the residual distances were significantly different compared to controls: right eye, P = 0.021, and left eye, P = 0.022. Color space configurations for the DM2 patients were compressed along the B0 Y and R 0 G dimensions. The present findings agree with earlier studies demonstrating diffuse losses in early stages of DM2. The proposed method of testing uses color spaces to represent discrimination and provides more differentiated quantitative diagnosis, which may be interpreted as the perceptual color system affected. In addition, it enables the detection of very mild color vision impairment that is not captured by the D-15d test. Along with fundoscopy, individual color spaces may serve for monitoring early functional changes and thereby to support a treatment strategy. Keywords: Color vision deficiency, Diabetes mellitus type 2, Lanthony D-15d, Multidimensional scaling, Color space Introduction Diabetes mellitus is accompanied by retinopathy, which may result in visual dysfunction, including color vision losses ~ Ismail & Whitaker, 1998!. In patients with type 2 diabetes mellitus ~ DM2! who developed diabetic retinopathy ~ DR!, losses in the B0 Y confusion axis ~tritan! have been reported and shown to increase with severity of DR ~ Barton et al., 2004; Fong et al., 1999; Ismail & Whitaker, 1998; Bresnick et al., 1985!. Color vision impairment may precede DR and emerge at early stages of DM2, before the appearance of vascular alterations in the retina. At this stage, predominantly tritan losses were found ~ Ismail & Whitaker, 1998!, but other authors reported diffuse losses as well ~ Trick et al., 1988; Ventura et al., 2003!. In most of these studies color vision was examined with arrangement tests, such as the Farnsworth-Munsell 100-hue test ~ FM-100!, or with the anomaloscope, to estimate Rayleigh ~red- green! and Moreland ~blue-green! matches ~e.g., Kurtenbach et al., 2002!. The outcome of the arrangement tests enables one, in the first place, to assess color vision loss ~i.e. whether blue-yellow ~ B0 Y! and 0or red-green ~ R 0 G! discrimination is impaired!. The FM-100 also provides an error score, which measures the overall loss of color discrimination. The anomaloscope matches give separate results for the two perceptual systems ~ B0 Y and R 0 G!, but the extrapolation from matching range to color impairment is far from direct. In this study we investigated color vision in patients with DM2 without DR, in an attempt to assess impairment of color discrim- ination quantitatively, in terms of distortions of a color space. This study belongs to a tradition of color research, in which subjects assess the dissimilarities they perceive among color stimuli, as a way of probing the forms of variation among those subjects ~ Helm, 1964; Paramei et al., 1991; Shepard & Cooper, 1992!. Address correspondence and reprint requests to: Claudia Feitosa San- tana, Depto. Psicologia Experimental, Instituto de Psicologia, Universidade de São Paulo, Av. Professor Mello Moraes, 1721 Bloco A Sala D-9-05508- 900 São Paulo, SP, Brasil. E-mail: claudia@feitosa-santana.com Visual Neuroscience ~2006!, 23, 663–668. Printed in the USA. Copyright © 2006 Cambridge University Press 0952-5238006 $16.00 DOI: 10.10170S0952523806233546 663