ODs may wish to incorporate color vision testing when working with patients having diabetes. A. Paul Chous, MA, OD, FAAO, CDE, talks about the importance of these tests, incorporating them into day-to-day exams, and devices available.
ODs must consider a more sophisticated color vision analysis for patients with diabetes. Color vision deficits in diabetes (and prediabetes) are common and may precede vascular retinopathy,1-3 worsen with progressing retinopathy-especially macular edema,4,5 and affect vision-related quality of life.6
Tracking threshold color vision changes over time appears to be a reasonable surrogate marker for worsening retinopathy and metabolic control. Analogous to threshold visual field stability or deterioration in patients with glaucoma, allowing for adjustment of our recommendations and therapeutic targets based on trend analysis (e.g., improved blood glucose control; color and contrast enhancing ophthalmic lenses; modification of the patient’s chromatic visual environment; and nutritional supplementation).7
Previously from Dr. Chous: Improving visual function, retinal integrity in DME patient
Diabetes is known to affect blue-yellow color vision per a number of reports.8-10 Tritan deficits are worse in those with diabetes and no retinopathy compared to age-matched controls. The severity of such defects is associated with increasing severity of diabetic retinopathy (see Figure 1).4
Abnormal Farnsworth-Munsell 100 hue test results, primarily blue-yellow deficits, have been associated with both diabetes and prediabetes (impaired fasting glucose and/or impaired glucose tolerance). Higher total error scores increase the odds of prediabetes or diabetes six to 13-fold independently of other risk factors. The risk of non-proliferative retinopathy increases more than 20-fold.11
Diabetes duration and mean glucose (as reflected by HbA1c) were shown to be associated with predominantly tritan defects in 849 subjects with type 2 diabetes and no ophthalmoscopic signs of retinopathy. Some 22 percent of patients demonstrated abnormalities using the far less sensitive Farnsworth D-15 color vision test.12
Automated color contrast threshold (CCT) testing is a more sensitive measure of color perception. It combines hue discrimination with reduced contrast optotype targets (letters or Landolt Cs) to isolate function of long (L), medium (M), and short (S) wavelength responsive cone cells and their attendant neural connections.
Diabetes affects S cone survivability and function for many reasons, including paucity of S cones, higher biochemical susceptibility of S cones to oxidative stress (due to preferential absorption of high-energy, short wavelength blue light), and post-photoreceptor elements that are easily damaged by hyperglycemic insult.13
Automated tritan contrast threshold (TCT) testing has been shown to correlate with sight-threatening diabetic retinopathy (94 percent sensitivity and 95 percent specificity) better than fundus photography, but the clinical and predictive utility of CCT for earlier stages of retinopathy has not been widely evaluated.14
Two commercially available CCT devices are available for assessing and monitoring acquired red-green and blue-yellow deficits with high statistical confidence: the Rabin Cone Contrast (Innova Systems) test and ColorDx CCT-HD (Konan Medical).
Of significance to time-pressed clinicians, CCT and TCT tests have shown high agreement with time-consuming “gold standard” anomaloscope testing.14,15
Sophisticated color vision assessment in diabetes gives vision researchers and ODs another noninvasive endpoint for clinical trials, new ophthalmic treatments and gauging efficacy of clinical recommendations such as blood glucose control. In addition to the 8 percent of males with inherited color vision anomalies, roughly 15 percent of the general population is believed to have acquired dyschromatopsia caused by a variety of common ocular conditions including cataracts, glaucoma, AMD, and diabetes.15
Our goal as ODs is to diagnose, ameliorate, and prevent visual function from worsening in our patients with diabetes and other disorders. ODs should also include careful evaluation of color perception in patients at increased risk.
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11. JoÃ „czyk-SkÃ³rka K, Kowalski J. [The evaluation of color vision and its diagnostic value in predicting the risk of diabetic retinopathy in patients with glucose metabolism disorders]. Pol Merkur Lekarski. 2017 Jul 21;43(253):15-21.
12. Tan NC, Yip WF, Kallakuri S, Sankari U, Koh YLE. Factors associated with impaired color vision without retinopathy amongst people with type 2 diabetes mellitus: a cross-sectional study. BMC Endocr Disord. 2017; 17: 29.
13. Cho NC, Poulsen GL, Ver Hoeve JN, Nork TM. Selective loss of S-cones in diabetic retinopathy. Arch Ophthalmol. 2000 Oct;118(10):1393-400.
14. Ong GL, Ripley LG, Newsom RS, Cooper M, Casswell AG. Screening for sight-threatening diabetic retinopathy: comparison of fundus photography with automated color contrast threshold test. Am J Ophthalmol. 2004 Mar;137(3):445-52.
15. Simunovic MP. Acquired color vision deficiency. Surv Ophthalmol. 2016 Mar-Apr;61(2):132-55.