Diabetes mellitus and the eye diseases connected with it comprise a set of complex disorder with multi factorial etiology, where both genetic and environmental factors play an active role. It is a substantial cause of environmental blindness in both the developed and developing countries. Newly diagnosed diabetic cases are increasing at an alarming rate in the developing countries like India due to better lifestyles and demographic right shift of the population, urbanization and differences in the access to the health care system. “Approximately, 382 million people across the world have been estimated to have been DM in 2013 and if no action is taken this number will rise to 592 million by 2035. WHO estimates that 19% of the worlds diabetic population lives in India and 80 million people in India will have Diabetes by the year 2030”.^[1]

“DR at present affects almost 100 million people worldwide and is set to become an ever-increasing health burden, with estimates between 1990 and 2010 showing that DR-related visual impairment and blindness increased by 64% and 27%, respectively ^[2]”

Thyroid diseases and diabetes mellitus are the two most common endocrine disorders encountered in clinical practice. Diabetes and thyroid disorders have been shown to mutually influence each other and a connection between both conditions has been reported in literature.^[3]

Thyroid disease is a pathological state that can adversely affect glycemic control in diabetics and has the potential to affect the health. Thyroid disease is found commonly in diabetes and is associated with advanced age, particularly in type 2diabetes and underlying autoimmune disease in type 1diabetes.^[4] Insulin and thyroid hormones are intimately involved in cellular metabolism and thus excess or deficit of either of these hormones result in the functional derangement of the other. The physiological and biochemical interrelationship between insulin and the influence of both insulin and iodothyronines on the metabolism of carbohydrates, proteins and lipids are recorded. Such findings indicate that iodothyronines are insulin antagonist with high levels being diabetogenic while absence of the hormone inhibits the development of diabetes.^[5] The thyroid hormone replacement is associated with a fall in glycosylated haemoglobin (HbA1c) level, which is influenced by increased erythropoiesis rather than by changes in glucose level.^[6]

The prevalence of SCH is 4–9% in the general population and our data suggests the same prevalence to be about 10.2% in T2DM population.^[7],^[8],^[9],^[10],^[11] Numerous studies propound that SCH is associated with hypertension, high cholesterol, and abnormal homocysteine level and patients with SCH have a higher risk of metabolic syndrome, atherosclerosis, cardiovascular events, and mortality.^[12],^[13],^[14]

The mechanism behind the association between DR and SCH may be the fall in circulating IGF-1, which is integral for a normal retinal vasculature, and the decrease of IGF-1 may be mediated by thyroid dysfunction.^[15]

Aim of our study was to find out the influence of SCH on diabetic retinopathy. If any connection between two exists, then routine screening or more frequent follow ups for thyroid patients may be considered desirable in type 2 diabetic subjects. This may also be helpful in investigating new tactics for preventing the development and/or progression of retinopathy.

Materials and Methods?

This cross-sectional study was conducted after taking ethical clearance from Institutional Ethical Committee, Jawaharlal Nehru Medical College and Hospital, A.M.U, Aligarh. Tenets of the Declaration of Helsinki were followed. An informed written consent was taken from each patient and\or patient attendant before participation in the study. The study population was drawn from the diabetic patients who attended the Rajiv Gandhi Center for Diabetes and Endocrinology, and subsequently were referred to the Retina Clinic, Institute of Ophthalmology, of the same hospital, for their ocular evaluation.

A clinical history was taken with the help of a structured questionnaire on a specially designed Performa (Appendix) including- demographic data, duration of diabetes, treatment taken, presence of any other complications of diabetes, addictions, dietary habits, family history of diabetes, and blood pressure.

The laboratory profile of each patient comprised of Blood sugar (both fasting greater than or equal to 126mg/dl in diabetes), HbA1C (greater than or equal to 6.5% in diabetes), thyroid hormones (reference range values serum T3 1.2 – 2.8 nmol/L, serum T4 60 – 160 nmol/L, serum TSH 0.17 – 5.0 mIU/L). The Thyroid profile was assessed by Beckman Coulter, Access 2, which uses the chemiluminescence immunoassay technique.

Total 60 patients with diabetes mellitus II were enrolled. 30 patients with diabetic retinopathy were taken as cases, while a similar number of patients without diabetic retinopathy were taken as controls. Known patients of type 1 diabetes mellitus (T1DM), autoimmune disorders, pregnancy, chronic renal failure and chronic liver disease, major depressive disorder, medications affecting thyroid hormones, Malignancies or history of chemotherapy or radiotherapy within past 1 year were excluded from the study.

A diagnosis of diabetic retinopathy was made when a patient exhibited a minimum of one microaneurysm in any field, as well as hemorrhages (dot, blot or flame shaped) and maculopathy (with or without clinically significant macular edema). The diagnosis of proliferative diabetic retinopathy was made only if there is neovascularization.

SPSS version 20 was used for analysis. Continuous variables were expressed as means, standard deviation (SD) and range. Independent and, paired t test were used as per the type of data. Non parametric, discrete data were evaluated using Chi square. Odds ratio was used to quantify the strength of association. Levene’s test was used to assess the equality of variances for a variable calculated across the two groups. The difference was considered significant at a p value of <0>

Result

60 type 2 diabetic subjects satisfying the inclusion criteria were selected from the individuals reporting at Rajeev Gandhi Centre of Endocrinology and Institute of Ophthalmology, Aligarh Muslim University, Aligarh and categorized into group A (cases) and group B (controls).

The clinical characteristics and biochemical data of the study participants are summarized in table I

Out of the 30 cases in group A (cases), 18 (60%) were female and 12(40%) were male. Among 30 individuals in group B (controls), 16 (53%) were female and 14 (46%) were male (Table-1). Mean age was 53.36 ± 7.69 years in cases and 53.89 ± 7.93 in controls. Descriptive statistics (Mean ± SD) for quantitative variables like age, HbA1c, serum TSH, free T3 and free T4 were measured for both groups as shown in table I and it revealed that Group A (cases) had higher mean serum TSH as compared to group B (controls).

SCH was diagnosed in 16 individuals (13 cases and 03 controls). Overall prevalence of SCH was 19.9% (24.3% in group A and 15.6% in group B). SCH was compared between the two groups by using Pearson Chi square test and it disclosed significantly higher prevalence of SCH in group A (p?0.05) as shown in table-2. Odds ratio was 1.738 (CI 1.129 – 2.917).

Table 1: Clinical characteristics and biochemical data of study participants