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dear editor: thank you for your letter ref. no 2003-2 dated 7 november 2010 regarding the comments of an ophthalmologist from thailand named professor viroj wiwan on my article titled “evaluation of contrast sensitivity, color vision and visual acuity in patients with and without diabetes”. he has suggested that the combination of existing tests may be a good way to increase the sensitivity of screening accuracy in diabetic patients, but reduce specificity and is not cost effective. i am grateful to professor viroj wiwan for this comment however it is evident that changes in visual function in diabetes occur before any structural abnormalities can be detected by ophthalmoscopy or even by fluorescein angiography.1 a reliable, quick and low cost test to detect early dysfunction is of vital importance to the screening and monitoring methods associated with both primary and shared care programs.2 in diabetes mellitus, functional abnormalities have been reported even with no or minimal diabetic retinopathy. these abnormalities include visual acuity, contrast sensitivity and color discrimination.3 we therefore concentrate upon the predictive ability of these tests, particularly since they are cost-effective and simple to administer. in our study, most tests display a gradual loss in performance on moving from nondiabetics to diabetics without retinopathy and onto diabetic, with increasing levels of retinopathy. both contrast sensitivity and color vision measurements identify a significant loss in performance between the normal and the diabetic groups without retinopathy.5     javad heravian, phd   associate professor of optometry   department of optometry   mashhad university of medical sciences   [email protected]   reference   1. gartaganis sp, psyrojannis aj, koliopoulos jx, mela ek. contrast sensitivity function in patients with impaired oral gluocose tolerance. optom vis sci 200178(3):157-61. 2. stavrou ep, wood jm. letter contrast sensitivity changes in early diabetic retinopathy. clin exp optom 200386(3):152-6. 3. wong r, khan j, adewoyin t, et al. the chroma test, a digital color contrast sensitivity analyzer, for diabetic maculopathy: a pilot study. bmc ophthalmol 20088:15. 4. abrishami m, heravian j, derakhshan a, et al. abnorml cambridge low-contrast grating sensitivity results associted with diabetic retinopathy as a potential screening tool. east mediterr health j 200713(4):810-8 . 5. heravian j, shoeibi n, azimi a, et al. evaluation of contrast sensitivity, color vision and visual acuity in patients with and without diabetes. iranian journal of ophthalmology 201022(3):33-40.