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Longer T2DM duration, older age tied to impaired colour vision

Tristan Manalac
06 Jun 2017
A GP who misdiagnosed a patient’s glaucoma - leading to her partial loss of vision - has been suspended by the SMC.

Impaired colour vision (ICV), mostly with tritanomaly, is common in type 2 diabetes mellitus (T2DM) patients without diabetic retinopathy, a new cross-sectional study shows. Moreover, advanced age and longer T2DM duration were risk factors for ICV.

“This is by far the largest study to determine the prevalence of ICV amongst multiethnic Asian people with T2DM. One in five (22.3%) was detected to have ICV, predominantly tritanomaly, using the D-15 test,” researchers said.

The investigators categorized 849T2DM patients (mean age 57.4±7.5 years; 49.4 percent male) into two according to the severity of ICV: strong or medium ICV (ICV+) and mild ICV or normal vision (ICV-). Severity was determined by the colour vision screening test using the Farnsworth D-15 instrument. Participants with type 1 diabetes mellitus and diabetic retinopathy, among other factors, were excluded.

Electronic health records of the participants were retrieved from the polyclinic study site in Eastern Singapore. Relevant information collected included T2DM duration, BMI, DM-related complications, treatment specifics, systolic (SBP) and diastolic (DBP) blood pressures, and other demographic information.

Of the total T2DM patients without diabetic retinopathy, 77.7 percent (n=660) were designated to the ICV- group while the remaining 22.3 percent (n=189) were positive for ICV. There were no significant differences in gender distribution (p=0.54), ethnicity distribution (p=0.19), BMI (p=0.57) and employment status (p=0.98). [BMC Endocr Disord 2017;17:29]

The prevalence and duration of hypertension (p=0.77 and p=0.05, respectively) and dyslipidaemia (p=0.56 and p=0.13, respectively), as well as the prevalence of coronary heart disease (p=0.49), stroke (p=0.40) and renal diseases (p=0.40) were also similar between both groups.

In contrast, those with ICV were significantly older (p<0.04) and had significantly longer DM duration (p<0.01). Of all the medications included in the analysis, only tolbutamide was significantly associated with ICV (p<0.01).

In terms of clinical variables, those with ICV had significantly lower mean low-density lipoprotein cholesterol (LDL-C; p<0.01), triglyceride (p=0.01) and total cholesterol (p=0.01) concentrations during the second year. Mean SBP (p=0.02) and DBP (p=0.01) during the second year was also significantly lower in the ICV+ group.

On the other hand, the mean high-density lipoprotein cholesterol (HDL-C) and HbA1c (p=0.01) concentrations during the second year was significantly higher in those with ICV (p=0.02).Moreover, the ICV+ group had significantly more individuals with visual acuity worse than 6/12 (p<0.01).

The most common type of ICV was tritanomaly with prevalence of 64.5 and 35.5 percent in the right and left eyes, respectively. This was followed by deutanomaly with corresponding prevalence of 70 and 30 percent. Protanomaly was the least common type of ICV and all reported cases were isolated to the left eye only.

Despite some existing evidence, the current literature is inconclusive about the potential pathological pathway that yields tritanomaly, the investigators wrote.

“Tritan defects have been explained by higher susceptibility of short-wavelength cones (S-cones) in postmortem examinations of the retina in a small study by Cho et al., and early yellowing of the lens in the diabetic eye,” researchers said. [Arch Ophthalmol 2000;118:1393-1400]

Logistic regression revealed that ICV was significantly associated with longer durations of DM (odds ratio [OR], 1.07; 95 percent CI, 1.02 to 1.12; p<0.01), higher age (OR, 1.04; 1.01 to 1.07; p=0.01), a prescription of tolbutamide (OR, 3.79; 1.65 to 8.74; p<0.01) and lower mean SBP during the second year (OR, 0.98; 0.96 to 0.99; p=0.01).

While previous studies have established the presence of ICV in early T2DM, none have yet to specify the least amount of time for the development of ICV. The present study thus shows that the risk of ICV increases every year after the onset of DM and that “[p]eople were more likely to develop ICV after 6 years.”

This also explains the statistical significance of advanced ages, the investigators said, as individuals who are older have had T2DM for a longer time.

The investigators recommend that since ICV can interfere with such routine and integral activities of life, “the introduction of colour vision screening for people with T2DM, possibly 6 years after its onset, could enhance the detection of ICV.”

However, “[a]ny screening programme should be simple, affordable, easy to implement and provides opportunities for effective intervention which will improve the health outcomes of the affected people,” they added.

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