|Year : 2012 | Volume
| Issue : 1 | Page : 129-134
Prevalence of visual impairment and associated risk factors in subjects with type II diabetes mellitus: Sankara Nethralaya diabetic retinopathy epidemiology and molecular genetics study (SN-DREAMS, report 16)
Padmaja Kumari Rani1, Rajiv Raman1, Laxmi Gella2, Vaitheeswaran Kulothungan3, Tarun Sharma1
1 Shri Bhagwan Mahavir Vitreoretinal Services, 18 College Road, Sankara Nethralaya, Chennai, Tamil Nadu, India
2 Elite School of Optometry, No. 8, G.S.T. Road, St. Thomas Mount, Chennai, Tamil Nadu, India
3 Department of Preventive Ophthalmology, 18 College Road, Sankara Nethralaya, Chennai, Tamil Nadu, India
|Date of Web Publication||20-Jan-2012|
Shri Bhagwan Mahavir Vitreoretinal Services, Sankara Nethralaya, 18 College Road, Chennai - 600006, Tamil Nadu
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Purpose: To report the prevalence of visual impairment (VI) and the associated risk factors in type II diabetic subjects.
Materials and Methods: The study included type II diabetes mellitus subjects who were enrolled from a cross-sectional study. Participants underwent biochemical testing and comprehensive ocular examination including stereo fundus photography. The VI was defined based on the World Health Organization criteria.
Results: The prevalence of VI was 4% in the cohort. The risk factors associated with the presence of VI included a female gender, age greater than 60 years, low socio-economic status, hypertension, microalbuminuria, macroalbuminuria, neuropathy, use of insulin and alcohol. Various ocular risk factors are nuclear sclerosis, subjects who have undergone cataract surgery, myopia and sight-threatening diabetic retinopathy (STDR). After adjusting for the factors using stepwise logistic regression analysis, hypertension, use of alcohol, post-cataract surgery and myopia were not risk factors. Stepwise logistic regression analysis indicated that VI was higher among subjects older than 60 years (odds ratio (OR): 4.95 [2.67-9.15]) and those who belonged to a low socio-economic status (OR: 2.91 [1.24-6.85]). The systemic risk factors for VI included microalbuminuria (OR: 2.91 [1.59-5.33]), macroalbuminuria (OR: 4.65 [1.57-13.77]) and presence of neuropathy (OR: 1.97 [1.09-3.59]) among subjects. Subjects with nuclear sclerosis (OR: 36.82 [11.12-112.36]) and presence of STDR (OR: 4.17 [1.54-11.29]) were at a higher risk of VI. Cataract was the most common cause of VI in the cohort.
Conclusion: Visual impairment, among type II diabetic subjects (4%), is a major public health problem that needs to be addressed. Cataract is the most common reversible cause of vision impairment in this population.
Keywords: Diabetes Mellitus, Prevalence, Risk factors, Visual Impairment
|How to cite this article:|
Rani PK, Raman R, Gella L, Kulothungan V, Sharma T. Prevalence of visual impairment and associated risk factors in subjects with type II diabetes mellitus: Sankara Nethralaya diabetic retinopathy epidemiology and molecular genetics study (SN-DREAMS, report 16). Middle East Afr J Ophthalmol 2012;19:129-34
|How to cite this URL:|
Rani PK, Raman R, Gella L, Kulothungan V, Sharma T. Prevalence of visual impairment and associated risk factors in subjects with type II diabetes mellitus: Sankara Nethralaya diabetic retinopathy epidemiology and molecular genetics study (SN-DREAMS, report 16). Middle East Afr J Ophthalmol [serial online] 2012 [cited 2017 Oct 18];19:129-34. Available from: http://www.meajo.org/text.asp?2012/19/1/129/92129
| Introduction|| |
Visual Impairment (VI) is a major public health problem worldwide. In 2002, there were more than 161 million visually impaired individuals globally, of whom about 37 million were blind. Without effective intervention, the number of blind people worldwide is projected to increase to 76 million by 2020.  In India, approximately 21.9 million people are disabled, and VI is the highest of all disabilities (48.5%). 
There is an alarming increase in the prevalence of diabetes worldwide. The World Health Organization (WHO) projects that India will have the highest number of diabetics: about 80 million by year 2030.  This increase will likely result in increased visual morbidity. The important causes of blindness in subjects with diabetes includes cataract, age-related macular degeneration, glaucoma and uncorrected refractive errors.  The National Health and Nutrition Survey conducted in the USA reported that VI was more common in diabetics than in non-diabetics.  The survey reported that approximately 11% of US adults with diabetes had some form of VI (7.2% correctable and 3.8% uncorrectable). Diabetic retinopathy accounted for 5% of the 37 million blind individuals worldwide. 
In India, there is limited data available on the prevalence of VI in diabetic subjects, particularly from a population-based sample. The present study was conducted to report the prevalence of VI and the associated risk factors in subjects with diabetes who were 40 years and older.
| Materials and Methods|| |
The study subjects were recruited from the Sankara Nethralaya Diabetic Retinopathy Epidemiology and Molecular Genetic Study (SN-DREAMS). The study design and research methodology of SN-DREAMS 1 is described in detail elsewhere. 
The study area was the Chennai metropolis with a population of 4.3 million, distributed in 155 divisions of ten zones. As a sample, a total of 5999 subjects from the general population aged >40 years were enumerated; multistage random sampling was stratified on the basis of the economic criteria. The data were compared between responders (1563, who visited the base hospital) and non-responders (253, who did not visit the base hospital) with regard to mean age, gender, diabetes status and mean fasting blood sugar. No statistically significant differences were observed.
Of the 5999 subjects enumerated, 1414 persons were identified with diabetes as based on the WHO criteria  (both known and newly diagnosed) and were analyzed for the study (96.20% response rate for first fasting blood sugar estimation, 85.60% response rate for base hospital examination, 8.7% turned out as non-diabetic after a second blood sugar test and 0.78% of retinal images were ungradable). The study was approved by the Institutional Review Board, and informed consent was obtained from subjects based on the tenets of the Helsinki Declaration.
Visual acuity assessment
The visual acuity was estimated using the modified ETDRS chart (Light House Low Vision Products, New York, NY, USA); for those who could not read the English alphabet, Landolt's ring test was used. Objective refraction (streak retinoscope, Beta 200, Heine, Germany) was always followed by a subjective refraction. If the subject was unable to read the 4/40 (log MAR 1.0) line, vision was checked at one meter, and if the subject was still unable to identify any of the larger optotype, perception of hand movements was assessed; and if the vision was less than hand movements, perception of light was tested.
Visual acuity in the better eye was considered for assessment of VI based on the WHO criteria.  Normal vision was considered if the visual acuity (VA) was better than 6/18, mild VI was considered if the VA was between 6/18 and 6/60, severe VI was considered if the VA was between 6/60 and 3/60 and blindness was considered if the VA was worse than 3/60.
Risk factor assessment
The risk factor analysis for VI included demographic, ocular and biochemical factors. The demographic risk factors studied were age, gender and socio-economic status (SES). The SES was stratified based on score: low SES (score, 0-14), middle SES (score, 15-28) and high SES (score, 29-42).  The systemic risk factors studied included the duration of diabetes mellitus, alcohol intake, smoking habits, family history of diabetes mellitus, neuropathy and nephropathy history (tingling, numbness, foot ulcers and amputated toe/foot) and diabetic treatment. The height and weight of all subjects was measured, and the body mass index (BMI)  was calculated using the formula: weight (kg)/height (m  ). Based on the BMI, individuals were classified as lean (male <20, female <19), normal (male 20-25, female 19-24), overweight (male 25-30, female 24-29) or obese (male >30, female >29).
The blood pressure was measured with sphygmomanometer with the patient in the sitting position. The patient was considered normoalbuminuric if albumin creatinine ratio (ACR) was less than 30 mg/g, microalbuminuria if ACR was between 30 and 300 mg/g and macroalbuminuria if ACR was above 300 mg/g.  Anemia was defined as a hemoglobin concentration of <13 g/dl in men and <12 g/dl in women.  Patients were considered positive for diabetic neuropathy if the vibration perception threshold (VPT) value was >20 V. 
The ocular risk factors included grading of lens opacities using the lens opacities classification system III (LOCS chart III, LeoT. Chylack, Harvard Medical School, Boston, MA); significant nuclear sclerosis was defined as nuclear opalescence of N2 or more. Ocular hypertension was defined as an IOP >21 mm Hg. The fundii of all patients were photographed using 45° four-field stereoscopic digital photography. Diabetic retinopathy was diagnosed based on the modified Klein classification.  For those who showed evidence of any retinopathy; an additional 30° seven-field digital stereo pairs were taken. All fundus photos were graded by two independent masked observers; the grading agreement was high (k = 0.83). 
Emmetropia was defined as a spherical equivalent between -0.50 and +0.50 diopter sphere (DS).  Myopia was defined as a spherical equivalent of less than -0.50 DS.  Hyperopia was defined as a spherical equivalent of greater than +0.50 DS.  Astigmatic correction was measured in minus cylinder format, and astigmatism was defined as a cylindrical error less than -0.50 diopter cylinder (DC) at any axis. 
Newly diagnosed diabetics were defined as patients with fasting blood glucose levels >110 mg/dl on two occasions.  Patients were considered to be known diabetics, if they were using hypoglycemic drugs, either oral or insulin or both.  Hypertensive patients were patients with blood pressures >140/90 mm Hg or if the patients were using anti-hypertensive drugs.  Glycemic control was categorized as normal (HbA 1c < 7) and abnormal (HbA 1c ≥7). High fasting plasma glucose was considered, if the value was >140 mg/dl. High serum triglycerides and high serum cholesterol were considered when the value was ≥150 mg/dl and 200 mg/dl, respectively. 
Statistical analyses were performed using the statistical software (SPSS for Windows, ver.13.0 SPSS Inc, Chicago, Il, USA). The results were expressed as percentage. The χ2 test was used to compare proportions amongst groups. Newly diagnosed diabetics were given a value of zero for the duration of diabetes. Univariate and stepwise logistic regression analyses were performed to study the effect of various risk factors using VI as the dependent variable. The P value of ≤0.05 was considered as significant.
| Results|| |
Out of the 1414 individuals with diabetes, 57 (4%) were visually impaired. Mild VI occurred in 3.6% (2.6-4.6) of subjects, severe VI occurred in 0.4% (0.07-0.7) and 0.1% (-0.06-0.4) were blind. Prevalence of all forms of VI was high among subjects with known diabetes compared to those with newly detected diabetes (4.8% vs 3.2%). Women had a higher prevalence of VI than men (5.8% vs 2.5%) and prevalence of VI increased with advancing age.
[Table 1] presents the various risk factors for VI in the study population. Women, advancing age, low and middle SES were identified as significant demographic risk factors. The significant systemic risk factors included the presence of hypertension, micro- and macro-albuminuria, presence of neuropathy and insulin users. Alcohol users showed less prevalence of VI. Biochemical risk factors such as fasting blood glucose, glycosylated hemoglobin, serum triglycerides and cholesterol did not show any association with prevalence of VI. Significant ocular risk factors were the presence of cataract, history of cataract surgery and presence of refractive error. The presence of diabetic retinopathy did not reveal any association with VI but STDR was a significant risk factor for VI.
[Table 2] presents the stepwise logistic regression analysis of risk factors for VI of the study cohort. After adjusting for the risk factors, stepwise logistic regression analysis showed that women were at higher risk of VI (OR: 2.18 (1.21-3.92)). Compared to those less than 60 years of age, the risk for VI increased in persons 60 years or older (OR: 4.95 (2.67-9.15)). Persons belonging to a low SES showed an increased prevalence of VI (OR: 2.91 (1.24-6.85)). Hypertension was as a significant risk factor for VI; however, after adjusting for the factors it was no longer a risk factor for VI. The significant systemic risk factors for VI included microalbuminuria - the risk for VI increased from 2.91 times to 4.65 times in the macroalbuminuric group. The risk of VI increased in the presence of neuropathy (OR: 1.97 (1.09-3.59)).
|Table 2: Stepwise multiple regression model for risk factors for visual impairment in the study population|
Click here to view
Significant ocular risk factors were presence of cataract, and there was increased risk of VI with increase in nuclear sclerosis (NS). Compared to the NS grades between 2.1 and 4.0, the risk of VI was 9.16 times in NS grades between 4.1 and 6.0, and the risk of VI was 36.82 times in NS grade greater than 6. A subject with a history of cataract surgery had a risk of developing VI (OR: 3.08 (1.75-5.42)); however, after adjusting for the other factors it was not a cause of VI. Presence of STDR was a significant risk factor for VI in the study population OR 4.17 (1.54-11.29). [Figure 1] presents the various causes of VI. Cataract (53%) was the most common cause of VI, followed by posterior capsular opacification (9%) and diabetic retinopathy (9%).
| Discussion|| |
The major findings of the present population-based study were the prevalence of VI (<20/40), which was found to be 4% in persons who is 40 years or older with type II diabetes. The prevalence of legal blindness was 0.5% (defined as 20/200 or worse). There is a paucity of population-based data in the literature about the prevalence of VI among people with diabetes. Klein et al,  in the Wisconsin study (1984) documented the prevalence of legal blindness (defined as 20/200 or worse) as 3.6% in persons with juvenile diabetes (diagnosed prior to 30 years of age and taking insulin) and 1.6% in persons with older onset diabetes (diagnosed at 30 years of age or older).
The prevalence of VI was more common in individuals with known diabetes than in newly diagnosed diabetics (4.2% vs 3.2%). A similar risk association with the duration of diabetes was documented by Klein et al.  The prevalence of VI was greater in women than in men with diabetes (5.7% vs 2.5%). These results were supported by other studies done in both persons with and without diabetes. , This could be due to lack of accessibility to healthcare resources based on gender disparity.
Advancing age is an important risk factor found in the present study. Subjects above 60 years were seven times more likely to develop VI. A similar observation was found in studies of subjects with and without diabetes. ,,, Low SES was found to be associated with an increased risk of VI (three times). The APEDS study of a population without diabetes found that subjects from a low SES were four times likely to develop VI. 
Among systemic risk factors both diabetic nephropathy (micro- and macroalbuminuria) and diabetic neuropathy were found to be significantly associated with VI. This shows the risk association of long-term diabetic complications with VI.
Among ocular risk factors, the presence of cataract was the most significant risk factor for VI. The odds of VI increased with cataract progression. These results concur with previous studies of subjects with and without diabetes. ,,, STDR showed a significant risk association with VI in our study. The largest proportion of VI is related to aging. Cataract was the most common cause of VI, followed by STDR. One limitation of our study is that we included only subjects with diabetes hence we couldn't differentiate causes of VI in the group of diabetics versus the group of non-diabetics.
In conclusion, in this study of an Indian cohort, the prevalence of VI is about 4% and legal blindness is about 0.5% in people with type II diabetes aged 40 or more. The demographic risk factors such as, advancing age, female gender, low SES, systemic risk factors such as nephropathy, neuropathy and ocular risk factors such as the presence of cataract and sight-threatening diabetic retinopathy were significantly associated with VI in type II diabetics. However risk factor of the cataract is negated after cataract surgery.
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[Table 1], [Table 2]
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