Older adults, diabetes mellitus and visual acuity: a community-based case control study

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1 Age and Ageing 2000; 29: Older adults, diabetes mellitus and visual acuity: a community-based case control study ALAN J. SINCLAIR, ANTONY J. BAYER 1,ALAN J. GIRLING 2,KEN W. WOODHOUSE , British Geriatrics Society Academic Department of Geriatric Medicine and Gerontology, Hayward Building, Selly Oak Hospital, Birmingham B29 6JD, UK 1 University Department of Geriatric Medicine, University of Wales College of Medicine, Llandough Hospital, Penarth, Wales, UK 2 Department of Mathematics and Statistics, University of Birmingham, Birmingham, UK Address correspondence to: A. J. Sinclair. Fax: (+ 44) a.j.sinclair@bham.ac.uk Abstract Main objectives: to screen for impaired distance visual acuity in older adults living at home, both with and without diabetes mellitus to determine whether diabetes increases the likelihood of visual impairment and to identify associated factors. Design: case control study. Settings: three districts of Wales: North Clwyd, Powys and South Glamorgan, with assessments in subjects homes. Subjects: 385 with diabetes mellitus and 385 age- and sex-matched controls. Main outcome measures: visual acuity measures, short form (SF)-36 quality of life scores Results: we observed impairment of visual acuity in 40% of those with diabetes mellitus and 31% of controls. Diabetes was associated with an increased risk of visual impairment [odds ratio 1.50 (95% confidence interval ), P = 0.013]. The pinhole test identified uncorrected refractive error in 11% of the 63 patients with diabetes and 12% of the 49 controls who wore glasses, and in 51% of the 91 patients and 84% of the 69 controls who did not wear glasses (P < 0.001). Increasing age (P < 0.001) and female sex (P = 0.014) were significantly associated with visual impairment in both groups, whilst history of foot ulceration (P = 0.001), duration of diabetes (P = 0.018) and treatment with insulin (P < 0.001) were significantly associated with visual impairment in subjects with diabetes. We observed a significant association between impaired visual acuity and five domains of the SF-36 (physical and social functioning, mental health, vitality, and health perceptions; P < 0.01 in each case). Conclusion: older adults living at home have a high prevalence of uncorrected visual impairment. Diabetes mellitus is associated with significantly increased risk of visual loss. This impairment is associated with detriments in health-related quality of life. We recommend earlier use of optometry services and assessment of visual acuity by clinicians. Keywords: aged, diabetes mellitus, quality of life, visual acuity Introduction Community-based surveys in Britain have demonstrated substantial undetected visual impairment in subjects aged 65 years and over [1, 2], with recent data indicating that 30% are visually impaired in both eyes [3]. Elderly people in institutions may be particularly vulnerable [4, 5]. Factors contributing to underreporting include lack of recognition of visual loss by the individual, a more disabling disorder masking perception of difficulties, fears about costs of treatment and a view that visual loss is expected in later life and cannot be ameliorated [6]. Loss of visual ability is associated with reduced quality of life and functional status [7], predisposition to falls and hip fracture [8, 9], and clinical depression [10]. Whilst ageing itself contributes to this impairment through pupillary miosis, deterioration in dark adaptation, loss of useful field of vision and loss of contrast sensitivity [11], the predominant visual disorders are age-associated macular degeneration, cataract, glaucoma and diabetes mellitus [12]. 335

2 A. J. Sinclair et al. Diabetic retinopathy is the third leading cause of blindness and partial sight registration in Britain [12] and diabetes mellitus imposes a markedly increased risk of developing cataract, glaucoma and retinal artery and vein thrombosis [13]. Diabetes-related visual disability may not only have the profound consequences seen in non-diabetic individuals but may also lead to treatment non-compliance, difficulties in insulin administration and glucose monitoring and inability to self-screen for diabetic complications. Our primary aims were to screen for impaired distance visual acuity in community living adults with and without diabetes mellitus aged 65 years and over. In addition, we aimed to determine whether diabetes increases likelihood of visual impairment and to identify associated factors. Subjects and methods We recruited subjects into a case control study as part of the All Wales Research into Elderly (AWARE) Diabetes Study. The cohort of patients identified included all those known to have diabetes mellitus who were aged 65 years or over in a sample of general practices in North, South and Mid-Wales. All met the World Health Organisation criteria for diagnosis of diabetes mellitus [14]. We sought additional and complementary information from medical records. Each patient was matched with a non-diabetic control subject who was next on the general practice register, of the same gender and whose date of birth was within 2 years of that of the patient. No control subject had a previous history of diabetes mellitus nor had been prescribed oral hypoglycaemic agents or insulin. Their non-diabetic status was subsequently confirmed by a fasting plasma glucose of 6.4 mmol/l, on the basis that until recently, a fasting level above 6.5 mmol/l was an indication for diagnostic testing when screening for diabetes mellitus [15]. Both cases and controls completed a comprehensive assessment lasting up to 2 h. Questionnaire information included demographic, medical, functional and social details corroborated from medical notes. Subjects also completed the Short Form 36 health survey (SF-36) as a measure of health-related quality of life [16]. Attendance at primary and secondary eye services was also documented. We recorded visual acuity with current glasses (if worn) in the subject s home under optimized lighting conditions (mornings only) using a directly illuminated 3-m Snellen chart with the subject sitting. Most subjects also had a pinhole refraction procedure (where initial visual acuity was worse than 6/6) which was used to identify uncorrected refractive error. For analysis, visual acuity data relate to measured visual acuity in the better eye with glasses (where usually worn). We used three visual acuity groupings: 6/12 or better; <6/12 to 6/60; and <6/60. We defined visual impairment as visual acuity <6/12 since this cutoff has been used previously [17]. Visual acuity of <6/ 60 is commonly used to classify people (with full field) as blind or partially sighted. In each case, measures of visual acuity were determined by highly trained diabetes mellitus research nurses with experience of diabetic and specialist eye clinics. Statistical methods We carried out formal analysis of visual impairment using binary logistic regression. The quoted odds ratio (OR) and 95% confidence interval (CI) for an individual factor represents the odds in favour of visual impairment for a subject in whom the factor is present relative to the corresponding odds for a similar subject in whom the factor is absent. For variables (such as age and SF-36 scores) the ORs represent the impact of a unit increase in the variable (per year in case of age). The natural range for SF-36 scores is 0 100, with higher scores corresponding to enhanced quality of life. For numerical convenience these scores were divided by 10 before analysis. Thus, the ORs in Table 4 are those associated with an increase of 10 units on the standard SF-36 scale. We performed the calculations using the MINITAB statistical package (Release 12.1, 1998). Results The study population consisted of 385 cases and 385 age- and sex-matched non-diabetic controls. Details are shown in Table 1. Subjects with diabetes mellitus had high levels of co-morbidity and diabetic complications similar to those reported in previous communitybased surveys [18], and a minority achieved good glycaemic control according to European Consensus Targets [19]. Prevalence of visual impairment and associated factors Visual impairment by the standard of best distance acuity of <6/12 was common (Table 2). Diabetes, however, was associated with significantly increased risk of visual impairment (P = 0.013). By use of a pinhole for identification of uncorrected refractive error we demonstrated that in those subjects with visual impairment wearing glasses at the time of testing, visual acuity improved in a small number of subjects with diabetes mellitus (seven out of 63, 11%) and in a similar number of controls (six out of 49, 12%). In visually impaired subjects who do not wear glasses, there was a significant difference between the proportion of diabetic subjects (46 out of 91, 51%) and the proportion of controls (58 out of 69, 84%) showing an 336

3 Diabetes and visual acuity in older people Table 1. Clinical characteristics of subjects with diabetes mellitus and non-diabetic controls Diabetic Non-diabetic Variable (n = 385) (n = 385) Age (years) (52%) 204 (53%) (37%) 143 (37%) (10%) 38 (10%) Sex (male/female) 191/ /193 Ethnic group White 371 (96%) 385 (100%) Asian 4 (1%) 0 Afro-Caribbean 10 (3%) 0 Home circumstances Lives alone 112 (29%) 123 (32%) Lives with others 249 (65%) 249 (65%) Lives in institution 24 ( 6%) 13 ( 3%) Median duration of diabetes, years 7.5 (3 14) (quartile range) Treatment of diabetes Diet only 91 (24%) Diet plus oral agents 223 (58%) Diet plus insulin 68 (18%) Mean fasting blood glucose, 11.2 (5.1) 5.3 (0.6) mmol/l (SD) Glycaemic control (HbA1c) a Good (<mean + 2 SD) 93 (27%) Borderline (<mean + 5 SD) 45 (42%) Poor (>mean + 5 SD) 104 (30%) a Not available for 43 subjects. Table 2. Visual acuity in subjects with diabetes and nondiabetic controls Diabetic Non-diabetic Visual acuity (n =385) (n =385) 6/12 or better 230 (60%) 266 (69%) Between 6/12 and 6/ (36%) 110 (29%) Worse than 6/60 15 ( 4%) 9 ( 2%) Odds ratio (calculated by combining all visual acuity scores worse than 6/12 in each group and adjusting for ethnic group) = 1.50 (95% confidence interval 1.09, 2.05). P-value = improved pinhole score [OR 5.16 (95% CI 2.40, 11.08), P < 0.001]. We investigated the influence of a large number of variables on the presence of visual impairment. As well as diabetes mellitus, increasing age (OR 1.08/year, 95% CI 1.06, 1.11; P < 0.001) and female sex (OR 1.49, 95% CI 1.08, 2.04; P = 0.014) were significantly associated with visual impairment. The ORs and P-values are quoted from a single logistic regression analysis of visual impairment on diabetic status, district, age, gender and ethnic group. After adjustment for these variables, a history of cataract and/or foot ulceration confirmed from medical records in 36 (9%) of the cases and 13 (3%) of the controls was significantly associated with visual impairment in diabetic subjects but not in controls (Table 3). Duration of diabetes mellitus and treatment with insulin were also associated with visual acuity <6/12, but glycaemic control had no significant influence. None of the other variables studied (smoking history, alcohol intake, history of glaucoma, peripheral or autonomic neuropathy, renal impairment, systolic and diastolic blood pressure) showed any association with visual impairment. Quality of life There was a significant association between presence of visual impairment and some, but not all, sub-scores of the SF-36 (Table 4). Physical and emotional role limitation, bodily pain and health change during the previous year were not associated. Contact with eye services In the preceding year, 150 subjects (39%) with diabetes mellitus and 216 controls (56%) had not seen an optician. Two hundred and fifty-seven (67%) of those with diabetes mellitus [versus 324 (85%) of controls] had either never been reviewed by an ophthalmologist or had not been seen within the previous 3 years. In 59 (15%) of subjects with diabetes mellitus, laser therapy had been carried out at some stage since diagnosis, and Table 3. Influence of significant variables on visual impairment after adjustment for age, sex, district and ethnic group Diabetic Non-diabetic Variable OR (95% CI) P-value OR (95% CI) P-value... History of cataract 1.64 (1.01, 2.63) (0.98, 3.14) History of foot ulcer 3.99 (1.79, 8.93) (0.24, 2.96) Duration of diabetes 1.03 a (1.01, 1.06) Treatment of diabetes Diet only 1.00 Diet plus oral agents 0.86 (0.49, 1.48) Diet plus insulin 3.81 (1.85, 7.84) <0.001 OR, odds ratio; CI, confidence interval. a Per year. 337

4 A. J. Sinclair et al. Table 4. Association between visual impairment and quality of life [measured by the Short Form 36 (SF-36)] after adjustment for age, sex, district, ethnic group and diabetic status SF-36 domain OR (95% CI) P-value Physical functioning 0.90 (0.85, 0.95) <0.001 Physical role limitation 0.96 (0.92, 1.01) Emotional role limitation 1.00 (0.94, 1.06) Social functioning 0.90 (0.86, 0.95) <0.001 General mental health 0.89 (0.82, 0.97) Vitality 0.91 (0.85, 0.97) Bodily pain 0.96 (0.91, 1.01) General health perceptions 0.90 (0.83, 0.97) Health change in previous year 1.03 (0.95, 1.10) OR, odds ratio; CI, confidence interval. Odds ratios are quoted per 10 SF-36 points. The greater the SF-36 score, the better the quality of life. 64 (17%) of the subjects with diabetes mellitus and 30 (8%) of controls had previously had cataract extraction. Of the 24 subjects with visual acuity <6/60, only six were registered blind and 11 as partially sighted. A further 38 (17 diabetic, 21 controls) who were registered as partially sighted or blind had visual acuity of 6/60 or better. Amongst the subjects with diabetes mellitus and visual impairment, 189 (69%) were responsible for taking their own diabetes mellitus treatment and other drug treatment and 208 (76%) for their own home monitoring of blood or urine glucose levels. Discussion In a large representative community sample of older people using a case control design, impairment of distance visual acuity was found in 40% of subjects with diabetes mellitus and 31% of controls, and the presence of diabetes mellitus was associated with a significantly increased risk of having poor vision (P = 0.013). Diabetic retinopathy may contribute to the increased risk but appears more influential in younger diabetic subjects [20]. History of cataract and glaucoma may be more important causes in older adults. This study was not designed to determine the primary cause of impairment, which would require fundoscopy and specialist examination. Reading and near-distance vision may also be more important than distance acuity in many older people and some may be reluctant to wear spectacles if near unaided vision is satisfactory. Based on pinhole determinations, we observed much uncorrected refractive error in both groups of study subjects and this may contribute to a considerable amount of remediable disability reported previously [1]. Where spectacles were not worn, more controls had evidence of refractive error. This may be partially explained by greater access to eye care services of subjects with diabetes mellitus. In diabetic subjects, visual impairment was related significantly to a history of cataract and/or foot ulceration, duration and treatment of diabetes mellitus. It is likely that the relationship between poorer vision and duration of diabetes mellitus involves increased retinopathy and cataract formation, whilst the link with foot ulceration may revolve around microvascular disease being a common aetiological mechanism for retinopathy and diabetic foot ulcers [21]. However, whilst some previous studies imply an association between good glycaemic control and less risk of retinopathy [22], we found no relationship between visual impairment and level of glycaemia. This suggests that retinopathy per se does not have a major influence on visual acuity, as was also suggested by the UK Prospective Diabetes Study [23]. The strong association between lower scores on the SF-36 quality of life measure and visual impairment was expected, since vision is one of the important senses (with hearing) required to sustain enjoyable and effective life in a community [16]. Poor vision is associated with increasing functional dependence and progression of disabilities [24, 25], and early identification of those with visual symptoms warrants greater attention [26]. The SF-36 was also used to explore vision-related health status in the Medical Outcomes Study [27], which found that frequent symptoms of blurred vision had demonstrable impacts on functioning and well-being. Regardless of treatment, improvement in quality of life has been observed when visual function improves [28] and the results of surgery for cataract in enhancing quality of life are generally positive [28, 29]. Few of our study cases had recent direct contact with eye care services. Deficiencies in providing effective eye health care for older people have been highlighted [1, 3], with the suggestion that there should be better integration of vision checks in the over-75s annual screening assessment undertaken by general practitioners. Although a recent systematic review indicates that screening for visual impairment of asymptomatic older people in the community is not justified [6], their conclusions are based to an extent on lack of appropriate and targeted interventions. We feel that in view of the substantial amount of uncorrected refractive error, greater use of optometry services and timely assessments by competent clinicians can do much to detect reversible visual impairment at an early stage. This measure is likely to have a positive impact on a patient s quality of life. Key points Undetected and uncorrected impairment of distance visual acuity is common in older people at home. Diabetes mellitus is a significant risk factor for lowering visual acuity. 338

5 Diabetes and visual acuity in older people Impaired visual acuity is associated with reduced quality of life in older people. Our observations reinforce need for greater use by older people of optometry services and for visual assessment by clinicians. Acknowledgements This study was supported by the Department of Health funded via the Welsh Office. Our thanks goes to Catherine Davies, Christine Corbett and Carys Brisbane for their commitment to the project and to the participating general practitioners. References 1. Wormald RP, Wright LA, Courtney P et al. Visual problems in the elderly population and implications for services. BMJ 1992; 304: Lavery JR, Gibson JM, Shaw DE et al. Vision and visual acuity in an elderly population. Ophthalmic Physiol Opt 1988; 8: Reidy A, Minassian DC, Vafidis G et al. Prevalence of serious eye disease and visual impairment in a north London population: population based, cross-sectional study. BMJ 1998; 316: Mitchell P, Hayes P, Wang JJ. Visual impairment in nursing home residents: the Blue Mountains Eye Study. Med J Aust 1997; 166: Perasalo R, Raitta C. Glaucoma of institutionalised geriatric patients. Acta Ophthalmol 1987; 182: Smeeth L, Illiffe S. Effectiveness of screening older people for impaired vision in community setting: systematic review of evidence from randomised controlled trials. BMJ 1998; 316: Scott IU, Schein OD, West S et al. Functional status and quality of life measurement among ophthalmic patients. Arch Ophthalmol 1994; 112: Ivers RQ, Cumming RG, Mitchell P et al. Visual impairment and falls in older adults: the Blue Mountains Eye Study. J Am Geriatr Soc 1998; 46: Dargent-Molina P, Favier F, Grandjean H et al. Fall-related factors and risk of hip fracture: the EPIDOS prospective study. Lancet 1996; 348: Rovner BW, Zisselman PM, Shmuely-Dulitzki Y. Depression and disability in older people with impaired vision: a follow-up study. J Am Geriatr Soc 1996; 44: Bellamy D. Ageing. A Biomedical Perspective. Chichester: John Wiley & Sons, 1995; Grey RHB, Burns-Cox CJ, Hughes A. Blind and partial sight registration in Avon. Br J Ophthalmol 1989; 73: Kohner EM. The lesions and natural history of diabetic retinopathy. In: Pickup J, Williams G eds. Textbook of Diabetes. Oxford: Blackwell Science, 1991; World Health Organisation. Diabetes Mellitus: report of a study group. WHO Technical Report series 727. Geneva: WHO, American Diabetes Association. Clinical Practice Recommendations Diabetes Care 1997; 20 (suppl. 1): S Stewart AL, Ware JE eds. Measuring Functioning and Well-being: the Medical Outcomes Study approach. Durham, NC: Duke University Press, West SK, Munoz B, Rubin GS et al. Function and visual impairment in a population-based study of older adults. The SEE Project. Invest Ophthamol Vis Sci 1997; 38: Neil HAW, Thompson AV, Thorogood M et al. Diabetes in the elderly: the Oxford community diabetes study. Diabetic Med 1989; 6: Alberti KGMM, Gries FA. Management of non-insulin-dependent diabetes mellitus: a consensus view. Diabetic Med 1988; 5: Klein R, Klein BE, Moss SE. Visual impairment in diabetes. Ophthalmology 1984; 91: McMillan DE. Development of vascular complications in diabetes. Vascular Med 1997; 2: Nathan DM, Singer DE, Godine JE et al. Retinopathy in older type 2 diabetics. Diabetes 1986; 35: UK Prospective Diabetes Study (UKPDS) Group. Intensive bloodglucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet 1998; 352: Jette AM, Branch LG. Impairment and disability in the aged. J Chronic Dis 1985; 38: La Forge RG, Spector WD, Sternberg J. The relationship of vision and hearing impairment to one-year mortality and functional decline. J Aging Health 1992; 4: Gray CS, Crabtree HL, O Connell JE et al. Waiting in the dark: cataract surgery for older people [Editorial]. BMJ 1999; 318: Lee PP, Spritzer K, Hays RD. The impact of blurred vision on functioning and well-being. Ophthalmology 1997; 104: Brenner MH, Curbow B, Javitt JC et al. Vision change and quality of life in the elderly. Response to cataract surgery and treatment of other chronic ocular conditions. Arch Ophthalmol 1993; 111: Desai P, Reidy A, Minassian DC et al. Gains from cataract surgery: visual function and quality of life. Br J Ophthalmol 1996; 80: Received 3 June 1999; accepted in revised form 18 October