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Age-related macular degeneration causing visual impairment in people 75 years or older in Britain
Age-Related Macular Degeneration Causing Visual Impairment in People 75 Years or Older in Britain An Add-on Study to the Medical Research Council Trial of Assessment and Management of Older People in the Community Jennifer R. Evans, MSc,1 Astrid E. Fletcher, PhD,2 Richard P. L. Wormald, FRCOphth1 Purpose: Age-related macular degeneration (AMD) is the most commonly occurring cause of visual loss in people registered as blind or partially sighted. There are no nationally representative data on the prevalence of AMD in the British population. We aimed to estimate the prevalence of AMD causing visual impairment in people 75 years or older in Britain. Design: Population-based cross-sectional study. Participants: Thirteen thousand nine hundred people 75 years or older in 49 practices taking part in the Medical Research Council Trial of the Assessment and Management of Older People in the Community. Methods: Trial nurses tested visual acuity in everyone 75 years or older in participating practices. We collected data on the cause of visual loss for everyone who was visually impaired. We obtained these data from review of the general practice medical notes and by sending a questionnaire to the hospital ophthalmologist. Visual impairment was defined as a binocular acuity of less than 6/18. Main Outcome Measure: Prevalence of AMD causing visual impairment. Results: There were 976 visually impaired people for whom a cause of visual loss was established. Of these, 516 (53%) had AMD as a cause of visual loss. We estimate that 3.7% (95% confidence interval, 3.2%– 4.2%) of the population 75 years or older and 14.4% (11.6%–17.2%) of the population 90 years or older are visually impaired due to AMD. There are an estimated 192 000 people 75 years or older visually impaired due to AMD in the United Kingdom (95% confidence interval, 144 000 –239 000). Conclusion: Our results, from the largest and most representative study of the causes of vision loss in older people in the British population, confirm the substantial burden of AMD in people 75 years and older. As the population ages, this problem will get worse. The needs of this group for vision aids and other support in the community should be addressed; research on the causes of AMD and possible preventive measures should be given priority. Ophthalmology 2004;111:513–517 © 2004 by the American Academy of Ophthalmology.
Age-related macular degeneration (AMD) is the most commonly occurring cause of visual loss in people registered as blind or partially sighted.1 A few small population-based studies have investigated the prevalence of AMD in defined geographical locations in England: a small town in Leicestershire,2 an outer area of North London,3 and a single Originally received: March 21, 2003. Accepted: July 17, 2003.
Manuscript no. 230157.
practice in inner London.4 There are no nationally representative data on the prevalence of AMD in the British population. A recent review pooled data from populationbased prevalence studies (largely outside the United Kingdom) and estimated that there are 214 000 (95% confidence interval [CI], 151 000 –310 000) people with AMD visually impaired to registrable levels in the United Kingdom.5 As part of the Medical Research Council (MRC) Trial of the Assessment and Management of Older People in the
1
Department of Epidemiology and International Eye Health, Institute of Ophthalmology, London School of Hygiene and Tropical Medicine, London, United Kingdom.
2
Centre for Ageing and Public Health, London School of Hygiene and Tropical Medicine, London, United Kingdom. The Medical Research Council Trial of the Assessment and Management of Older People in the Community was funded by the United Kingdom Medical
© 2004 by the American Academy of Ophthalmology Published by Elsevier Inc.
Research Council, the Department of Health, and the Scottish Office. Collection of data on causes of visual impairment was funded by the Gift of Thomas Pocklington. Correspondence to Ms. Jennifer Evans, International Centre for Eye Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom. ISSN 0161-6420/04/$–see front matter doi:10.1016/j.ophtha.2003.07.012
513
Ophthalmology Volume 111, Number 3, March 2004 Community, almost 15 000 people 75 years and older had a visual acuity test.6 An add-on study to the main trial established the cause of visual loss in people identified with visual impairment in this group.7 We aimed to estimate the burden of AMD causing visual impairment in this agegroup in the United Kingdom.
Materials and Methods The MRC Trial of the Assessment and Management of Older People in the Community is a large-cluster randomized trial taking place in 106 general practices from the MRC General Practice Research Framework.8 The practices in the study were selected to be representative of the mortality (standardized mortality ratio) and Jarman scores of general practices in Britain (England, Wales, and Scotland). All patients 75 years or older on the general practitioner list were invited to participate in the trial, unless they were in long-stay hospitals or nursing homes (⬍4% of the target population) or were terminally ill (⬍1%). The trial was approved by the relevant local research ethics committees. People in 53 randomly allocated practices were given a detailed health assessment by the practice nurse, including a visual acuity test. Visual acuity was measured at 3 m with a Glasgow Acuity Chart.9 This chart follows the principles of the Bailey–Lovie chart10 and measures the minimal angle of resolution on a logarithmic scale (logarithm of the minimum angle of resolution). Ninety-five percent of vision measurements made with the Glasgow Acuity Chart differ by less than 0.07 log units, relative to the Bailey–Lovie chart.11 Binocular vision was measured first, followed by vision in the right and left eyes. All vision measurements were conducted with usual spectacle correction. People with visual acuity of ⱖ0.5 in either eye (equivalent to less than 6/18 Snellen acuity) were retested with a pinhole occluder. People with pinhole vision of less than 6/18 in either eye were referred to the hospital eye service, if the vision loss had not been previously investigated. Forty-nine of 53 practices took part in the study on the causes of visual loss.12 The main cause of visual impairment was taken to be the cause of visual loss in the eye that lost vision last. The cause of visual impairment was identified from the general practitioner notes. Research nurses abstracted correspondence relating to eye disease, and this was coded twice by Dr Evans. The following coding schema was used for AMD: 1. Definite AMD, type unspecified. The following terms: ● Age-related macular degeneration or senile macular degeneration. 2. Definite neovascular AMD. The following terms in conjunction with a diagnosis of AMD: ● Neovascular, exudative, disciform, pigment epithelial detachment, wet. ● Any terms relating to new vessel growth and/or leakage/ hemorrhage in the retina. 3. Definite geographic atrophy/late-stage AMD. ● A diagnosis of AMD combined with any definite statement that the condition was “dry” or that there was no evidence of new vessels/leakage on fluorescein angiography. 4. Possible AMD. ● Macular degeneration/disturbance with onset after 50 with no obvious cause but that was not directly described by the ophthalmologist as “age related.” This was also subdivided into neovascular disease and geographic atrophy according to the definitions above.
514
● Age-related macular degeneration or macular degeneration described by an optician or other health professional. The cause of visual loss established from the general practitioner notes was validated by means of a hospital consultant questionnaire. Information from the hospital consultant was available for 48% of forms. One reminder letter was sent to consultants who did not reply. All data were collected on anonymous forms that were identified only by a unique identification number. As this was data collection beyond that originally in the protocol for the MRC Elderly Trial, we obtained approval from the relevant local research ethics committees. Measurements of visual acuity were made between 1995 and 1998; data collection on cause of visual loss took place between 1996 and 2000. In the MRC Trial, treatments were assigned at the general practice level; therefore general practices, rather than individual patients, were selected to take part in the study. Observations on individuals within the same general practice may be correlated. Ignoring the extra variation introduced by clustering may lead to an incorrect interpretation, as CIs, in general, will be narrower and P values smaller than they should be. The clustered design of the study was taken into account in the analysis using the svy commands in Stata (Stata Corp., College Station, TX). These commands calculate standard errors and 2 values, adjusted for the extra variation introduced by the design of the study.12,13
Results Response rates for visual acuity testing have been published elsewhere.6 Briefly, there were 21 241 eligible people in 53 general practices. Of these, 15 126 (71%) had a detailed health assessment. People taking part in the study had ages (median age, 80.3 years [interquartile range, 77.2– 84.2]) similar to those not taking part (median age, 81.0 [interquartile range, 77.7– 85.2]). Details of the causes of visual impairment study have been published previously.7 In brief, practices taking part in the cause of visual impairment study (n ⫽ 49) and the 4 practices that declined to take part had similar sizes, levels of visual impairment, and age and gender distributions. In these 49 practices, there were 1742 people who had a binocular acuity of less than 6/18. Of these, 450 (26%) achieved a pinhole acuity of better than or equal to 6/18 in the better eye. In these people the principle cause of visual impairment was considered to be refractive error. Cause of visual loss was available for 976 (76%) of the remaining 1292 visually impaired people. People for whom data on the cause of visual loss were available were similar in terms of age and gender to those for whom data were not available. However, they had worse visual acuity—25.5% had a visual acuity of less than 3/60, compared with 12.2% of people for whom cause of visual loss was not available. There was little difference between people with data on cause of visual loss and those without in terms of risk factors for AMD such as smoking (design-based 2 ⫽ 0.849, P ⫽ 0.430). Table 1 shows the distribution of AMD. In total, there were 976 visually impaired people for whom a cause of visual loss was identified. Of these, 516 were identified as having AMD as a cause of visual loss. Of these 516 people, 428 (83%) had definite AMD, and a further 88 had possible AMD. There were a total of 467 people who had information from both the hospital and general practice notes. For AMD, in 239 cases the hospital and general practice agreed that AMD was the main or contributory cause; in 156 cases they agreed that AMD was not a main or contributory cause. In 39 cases the general practice notes suggested that AMD was a main or contributory cause, but the hospital consultant disagreed, whereas in 33 cases the opposite was true. This gives a percentage agreement of 395/467 ⫽ 85% ( ⫽ 0.68).
Evans et al 䡠 AMD Causing Visual Impairment in Older People in Britain Table 1. Age-Related Macular Degeneration (AMD) N Total no. of visually impaired people with cause of visual loss identified Non-AMD cause Possible AMD Definite AMD
976 458 88 428
Table 2. Subtypes of Age-Related Macular Degeneration (AMD) % N
100 46.9 9.0 43.9
Table 2 shows the different subtypes of AMD identified. In 26% of cases it was not possible to identify a subtype. In 34% neovascular AMD was identified, and in 40% geographic atrophy/ late-stage AMD was identified. Table 3 shows the age-specific prevalence rates of AMD causing visual impairment. Overall, 3.7% (95% CI, 3.2%– 4.2%) of our sample of people 75 years or older were visually impaired due to AMD. There was a higher rate in women (4.4%) than in men (2.6%) (design-based 2 ⫽ 48.1, P⬍0.0001). There was a strong relationship with age: 1.1% of the 75- to 79-year-old age group were visually impaired due to AMD, compared with 14.4% of people 90 years or older (design-based 2 ⫽ 143.9, P⬍0.0001). Women had a higher rate than men at all ages. The odds ratio (OR) of AMD causing visual impairment in women versus men, controlled for age, was 1.44 (95% CI, 1.22–1.69). Applying these figures to the United Kingdom population in 2001,14 there are estimated to be 192 000 people 75 years or older visually impaired due to AMD (144 000 –239 000) living in the United Kingdom. Of these, 146 000 (76%) are women. These age-specific prevalence rates are calculated assuming that the prevalence of visual impairment in the 31% of people who did not attend the examination was similar to that of those who attended and had vision measured. There was also a group of people who were known to be visually impaired but for whom no cause of visual loss was established. We have calculated the prevalence rates assuming that none of these people had visual loss due to AMD. This gives a conservative measure of prevalence. Table 3 also shows the prevalence recalculated excluding people with an unknown cause of visual loss from the denominator. This suggests that the prevalence of AMD in people with an unknown cause of visual loss is similar to that in people with a known cause. This results in a less conservative estimate of the prevalence of AMD causing visual impairment. These figures indicate that as many as 1 in 5 women 90 years or older may be visually impaired due to AMD. Table 4 shows the prevalence of AMD causing severe visual impairment (binocular acuity less than 6/60). The overall prevalence in people 75 years or older was 1.6% (95% CI, 1.3%–1.9%). As for AMD causing visual impairment, the prevalence increased sharply with increasing age. At ages 90 and above, the prevalence was 6.6% (95% CI, 4.8%– 8.4%). Women had a higher rate at all ages. The OR of AMD causing severe visual impairment in women versus men, controlled for age, was 1.40 (95% CI, 1.04 –1.89).
Discussion We estimate that 3.7% (95% CI, 3.2%– 4.2%) of the population 75 years or older has AMD causing visual impairment. The prevalence increases rapidly with increasing age—14.4% (11.6%–17.2%) of the population 90 years or older are visually impaired due to AMD. Applying the age-specific prevalence rates to the United Kingdom population gives an estimated 192 000 people 75 years or older
Total no. of visually impaired people with definite AMD identified as a cause of visual loss Type unspecified Neovascular AMD Geographic atrophy/late-stage AMD
428 112 144 172
% 100 26.2 33.6 40.2
visually impaired due to AMD in the United Kingdom (95% CIs, 144 000 –239 000). The MRC Trial of the Assessment and Management of Older People in the Community was a large populationbased trial, recruiting participants 75 years or older from general practices selected to be representative of the British population. The size of the study enabled us to identify a large group of people visually impaired due to AMD. However, the size and geographical spread of practices, combined with the age of the participants, meant that we were unable to arrange for a standardized ophthalmic examination of everyone identified as visually impaired during the trial. People who were newly identified as visually impaired were referred to the hospital eye service. Using a combination of medical record review in the general practice and a hospital ophthalmologist questionnaire, we were able to establish the cause of visual loss in 76% of people with a pinhole-corrected acuity of less than 6/18 in the better eye. We had good agreement at the hospital and general practice level. However, our method of case ascertainment must be considered less robust than a cross-sectional survey using standardized methods. In a recent review pooling data from several international studies of AMD, prevalences of visual impairment due to AMD were estimated as 1.6% (75–79 years), 3.6% (80 – 84), 8.1% (85– 89), and 15.3% (ⱖ90).5 These results compare well with the estimates of prevalence from the current study: 1.1%, 3.6%, 8.1%, and 14.4%. Owen et al estimated that there are currently 214 000 (151 000 –310 000) with visual impairment caused by AMD (visual acuity of 6/18 or worse).5 This is slightly higher than the estimate from this study (192 000 [95% CI, 144 000 –239 000]). However, reflecting the relatively large number of cases in the current study, our CIs are substantially narrower. If we adjust for missing data in our study, we estimate somewhat higher prevalence rates. However, we are then making various assumptions about the nature of the people for whom a cause of visual loss was not available. These people were less likely to be blind than people for whom the cause of visual loss was available. It may well be that they were not as affected by AMD. There are several reasons why this study will have underestimated the burden of AMD in this age group: 1. As the MRC Trial was a pragmatic assessment of simple assessment methods in general practice, the cutoff for referral was less than 6/18. When assessing the cause of visual impairment, we were restricted to this cutoff as well. This means that we are likely to
515
Ophthalmology Volume 111, Number 3, March 2004 Table 3. Age-Specific Prevalence of Age-Related Macular Degeneration Causing Binocular Visual Impairment of Less than 6/18 Prevalence Excluding People with No Information on Cause of Visual Impairment from Denominator
Minimum Prevalence
All ages Total Men Women Men and women 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs Men 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs Women 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs
N
% Prevalence
SE
95% CI
N
% Prevalence
SE
95% CI
13 900 5357 8543
3.7 2.6 4.4
0.245 0.247 0.286
3.2–4.2 2.1–3.1 3.8–5.0
13 584 5269 8315
3.8 2.6 4.6
0.252 0.250 0.296
3.3–4.3 2.1–3.1 4.0–5.1
6582 4388 2186 744
1.1 3.6 8.1 14.4
0.130 0.325 0.825 1.395
0.9–1.4 3.0–4.3 6.4–9.7 11.6–17.2
6516 4305 2098 665
1.1 3.7 8.4 16.1
0.132 0.334 0.862 1.603
0.9–1.4 3.0–4.4 6.7–10.1 12.9–19.3
2831 1623 729 174
0.9 2.9 6.2 11.5
0.187 0.360 0.885 2.287
0.5–1.3 2.2–3.6 4.4–8.0 6.9–16.1
2808 1598 704 159
0.9 2.9 6.4 12.6
0.188 0.366 0.906 2.526
0.5–1.3 2.2–3.7 4.6–8.2 7.5–17.7
3751 2765 1457 570
1.3 4.1 9.0 15.3
0.191 0.435 0.994 1.646
0.9–1.7 3.2–4.9 7.0–11.0 12.0–18.6
3708 2707 1394 506
1.3 4.1 9.4 17.2
0.193 0.450 1.040 1.892
0.9–1.7 3.2–5.0 7.3–11.5 13.4–21.0
CI ⫽ confidence interval; SE ⫽ standard error.
have underestimated the impact of AMD, as many people will be visually impaired to lesser levels. A visual acuity of less than 6/12 but greater than 6/18 will have many disadvantages—for example, inability to drive. 2. The MRC Trial did not include people in long-term nursing care. Other studies have shown a high prevalence of visual impairment in nursing homes. For example, in people 85 years or older taking part in the National Diet and Nutrition Study, 30% of those
living in the community were visually impaired (less than 6/18), compared with 47% of those living in residential nursing homes.15 Our results, from the largest and most representative study of the causes of vision loss in older people in the British population, indicate that nearly 200 000 people 75 years or older are visually impaired due to AMD in the United Kingdom. As the population ages, this figure will rise. The needs of this group for vision aids and other
Table 4. Age-Specific Prevalence of Age-Related Macular Degeneration Causing Binocular Visual Impairment of Less than 6/60
All ages Total Men Women Men and Women 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs Men 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs Women 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs
N
% Prevalence
SE
95% CI
13 900 5357 8543
1.6 1.1 1.9
0.141 0.152 0.175
1.3–1.9 0.8–1.4 1.5–2.2
6582 4388 2186 744
0.3 1.7 3.2 6.6
0.069 0.207 0.473 0.879
0.2–0.5 1.3–2.1 2.3–4.2 4.8–8.4
2831 1623 729 174
0.2 1.5 2.1 6.3
0.082 0.281 0.501 1.767
0.1–0.4 1.0–2.1 1.0–3.1 2.8–9.9
3751 2765 1457 570
0.4 1.8 3.8 6.7
0.100 0.267 0.610 0.898
0.2–0.6 1.3–2.4 2.6–5.1 4.9–8.5
CI ⫽ confidence interval; SE ⫽ standard error.
516
Evans et al 䡠 AMD Causing Visual Impairment in Older People in Britain support in the community should be addressed; research on the causes of AMD and possible preventive measures should be given priority.
7.
References
8.
1. Evans JR. Causes of blindness and partial sight in England and Wales 1990-1991 [Studies on Medical and Population Subjects 57]. London: Her Majesty’s Stationery Office; 1995. 2. Dickinson AJ, Sparrow JM, Duke AM, et al. Prevalence of age-related maculopathy at two points in time in an elderly British population. Eye 1997;11:301–14. 3. 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: 1643– 6. 4. Wormald RP, Wright LA, Courtney P, et al. Visual problems in the elderly population and implications for services. BMJ 1992;304:1226 –9. 5. Owen CG, Fletcher AE, Donoghue M, Rudnicka AR. How big is the burden of visual loss caused by age related macular degeneration in the United Kingdom? Br J Ophthalmol 2003; 87:312–7. 6. Evans JR, Fletcher AE, Wormald RP, et al. Prevalence of visual impairment in people aged 75 years and older in Britain: results from the MRC trial of assessment and management
9.
10. 11.
12. 13.
14. 15.
of older people in the community. Br J Ophthalmol 2002;86: 795– 800. Evans JR, Fletcher AE, Wormald RPL. Causes of visual impairment in people aged 75 years and above in Britain. Br J Ophthalmol. In press. Fletcher AE, Jones DA, Bulpitt CJ, Tulloch AJ. The MRC Trial of assessment and management of older people in the community: objectives, design and interventions [ISRCTN23494848]. BMC Health Serv Res 2002;2:21. McGraw PV, Winn B. Glasgow Acuity Cards: a new test for the measurement of letter acuity in children. Ophthalmic Physiol Opt 1993;13:400 – 4. Bailey IL, Lovie JE. New design principles for visual acuity letter charts. Am J Optom Physiol Opt 1976;53:740 –5. McGraw PV, Winn B, Gray LS, Elliott DB. Improving the reliability of visual acuity measures in young children. Ophthalmic Physiol Opt 2000;20:173– 84. Skinner CJ, Holt D, Smith TMF, eds. Analysis of Complex Surveys. New York: John Wiley & Sons; 1989. Eltinge JL, Sribney WM. Some basic concepts for designbased analysis of complex survey data. Stata Tech Bull 1996; 31:3– 6. Available at: http://www.gad.gov.uk/population/1998/ pop5yearuk98 – 08.html. Accessed June 24, 2002. van der Pols JC, Bates CJ, McGraw PV, et al. Visual acuity measurements in a national sample of British elderly people. Br J Ophthalmol 2000;84:165–70.
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Age-related macular degeneration (AMD) is the most commonly occurring cause of visual loss in people registered as blind or partially sighted.1 A few small population-based studies have investigated the prevalence of AMD in defined geographical locations in England: a small town in Leicestershire,2 an outer area of North London,3 and a single Originally received: March 21, 2003. Accepted: July 17, 2003.
Manuscript no. 230157.
practice in inner London.4 There are no nationally representative data on the prevalence of AMD in the British population. A recent review pooled data from populationbased prevalence studies (largely outside the United Kingdom) and estimated that there are 214 000 (95% confidence interval [CI], 151 000 –310 000) people with AMD visually impaired to registrable levels in the United Kingdom.5 As part of the Medical Research Council (MRC) Trial of the Assessment and Management of Older People in the
1
Department of Epidemiology and International Eye Health, Institute of Ophthalmology, London School of Hygiene and Tropical Medicine, London, United Kingdom.
2
Centre for Ageing and Public Health, London School of Hygiene and Tropical Medicine, London, United Kingdom. The Medical Research Council Trial of the Assessment and Management of Older People in the Community was funded by the United Kingdom Medical
© 2004 by the American Academy of Ophthalmology Published by Elsevier Inc.
Research Council, the Department of Health, and the Scottish Office. Collection of data on causes of visual impairment was funded by the Gift of Thomas Pocklington. Correspondence to Ms. Jennifer Evans, International Centre for Eye Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom. ISSN 0161-6420/04/$–see front matter doi:10.1016/j.ophtha.2003.07.012
513
Ophthalmology Volume 111, Number 3, March 2004 Community, almost 15 000 people 75 years and older had a visual acuity test.6 An add-on study to the main trial established the cause of visual loss in people identified with visual impairment in this group.7 We aimed to estimate the burden of AMD causing visual impairment in this agegroup in the United Kingdom.
Materials and Methods The MRC Trial of the Assessment and Management of Older People in the Community is a large-cluster randomized trial taking place in 106 general practices from the MRC General Practice Research Framework.8 The practices in the study were selected to be representative of the mortality (standardized mortality ratio) and Jarman scores of general practices in Britain (England, Wales, and Scotland). All patients 75 years or older on the general practitioner list were invited to participate in the trial, unless they were in long-stay hospitals or nursing homes (⬍4% of the target population) or were terminally ill (⬍1%). The trial was approved by the relevant local research ethics committees. People in 53 randomly allocated practices were given a detailed health assessment by the practice nurse, including a visual acuity test. Visual acuity was measured at 3 m with a Glasgow Acuity Chart.9 This chart follows the principles of the Bailey–Lovie chart10 and measures the minimal angle of resolution on a logarithmic scale (logarithm of the minimum angle of resolution). Ninety-five percent of vision measurements made with the Glasgow Acuity Chart differ by less than 0.07 log units, relative to the Bailey–Lovie chart.11 Binocular vision was measured first, followed by vision in the right and left eyes. All vision measurements were conducted with usual spectacle correction. People with visual acuity of ⱖ0.5 in either eye (equivalent to less than 6/18 Snellen acuity) were retested with a pinhole occluder. People with pinhole vision of less than 6/18 in either eye were referred to the hospital eye service, if the vision loss had not been previously investigated. Forty-nine of 53 practices took part in the study on the causes of visual loss.12 The main cause of visual impairment was taken to be the cause of visual loss in the eye that lost vision last. The cause of visual impairment was identified from the general practitioner notes. Research nurses abstracted correspondence relating to eye disease, and this was coded twice by Dr Evans. The following coding schema was used for AMD: 1. Definite AMD, type unspecified. The following terms: ● Age-related macular degeneration or senile macular degeneration. 2. Definite neovascular AMD. The following terms in conjunction with a diagnosis of AMD: ● Neovascular, exudative, disciform, pigment epithelial detachment, wet. ● Any terms relating to new vessel growth and/or leakage/ hemorrhage in the retina. 3. Definite geographic atrophy/late-stage AMD. ● A diagnosis of AMD combined with any definite statement that the condition was “dry” or that there was no evidence of new vessels/leakage on fluorescein angiography. 4. Possible AMD. ● Macular degeneration/disturbance with onset after 50 with no obvious cause but that was not directly described by the ophthalmologist as “age related.” This was also subdivided into neovascular disease and geographic atrophy according to the definitions above.
514
● Age-related macular degeneration or macular degeneration described by an optician or other health professional. The cause of visual loss established from the general practitioner notes was validated by means of a hospital consultant questionnaire. Information from the hospital consultant was available for 48% of forms. One reminder letter was sent to consultants who did not reply. All data were collected on anonymous forms that were identified only by a unique identification number. As this was data collection beyond that originally in the protocol for the MRC Elderly Trial, we obtained approval from the relevant local research ethics committees. Measurements of visual acuity were made between 1995 and 1998; data collection on cause of visual loss took place between 1996 and 2000. In the MRC Trial, treatments were assigned at the general practice level; therefore general practices, rather than individual patients, were selected to take part in the study. Observations on individuals within the same general practice may be correlated. Ignoring the extra variation introduced by clustering may lead to an incorrect interpretation, as CIs, in general, will be narrower and P values smaller than they should be. The clustered design of the study was taken into account in the analysis using the svy commands in Stata (Stata Corp., College Station, TX). These commands calculate standard errors and 2 values, adjusted for the extra variation introduced by the design of the study.12,13
Results Response rates for visual acuity testing have been published elsewhere.6 Briefly, there were 21 241 eligible people in 53 general practices. Of these, 15 126 (71%) had a detailed health assessment. People taking part in the study had ages (median age, 80.3 years [interquartile range, 77.2– 84.2]) similar to those not taking part (median age, 81.0 [interquartile range, 77.7– 85.2]). Details of the causes of visual impairment study have been published previously.7 In brief, practices taking part in the cause of visual impairment study (n ⫽ 49) and the 4 practices that declined to take part had similar sizes, levels of visual impairment, and age and gender distributions. In these 49 practices, there were 1742 people who had a binocular acuity of less than 6/18. Of these, 450 (26%) achieved a pinhole acuity of better than or equal to 6/18 in the better eye. In these people the principle cause of visual impairment was considered to be refractive error. Cause of visual loss was available for 976 (76%) of the remaining 1292 visually impaired people. People for whom data on the cause of visual loss were available were similar in terms of age and gender to those for whom data were not available. However, they had worse visual acuity—25.5% had a visual acuity of less than 3/60, compared with 12.2% of people for whom cause of visual loss was not available. There was little difference between people with data on cause of visual loss and those without in terms of risk factors for AMD such as smoking (design-based 2 ⫽ 0.849, P ⫽ 0.430). Table 1 shows the distribution of AMD. In total, there were 976 visually impaired people for whom a cause of visual loss was identified. Of these, 516 were identified as having AMD as a cause of visual loss. Of these 516 people, 428 (83%) had definite AMD, and a further 88 had possible AMD. There were a total of 467 people who had information from both the hospital and general practice notes. For AMD, in 239 cases the hospital and general practice agreed that AMD was the main or contributory cause; in 156 cases they agreed that AMD was not a main or contributory cause. In 39 cases the general practice notes suggested that AMD was a main or contributory cause, but the hospital consultant disagreed, whereas in 33 cases the opposite was true. This gives a percentage agreement of 395/467 ⫽ 85% ( ⫽ 0.68).
Evans et al 䡠 AMD Causing Visual Impairment in Older People in Britain Table 1. Age-Related Macular Degeneration (AMD) N Total no. of visually impaired people with cause of visual loss identified Non-AMD cause Possible AMD Definite AMD
976 458 88 428
Table 2. Subtypes of Age-Related Macular Degeneration (AMD) % N
100 46.9 9.0 43.9
Table 2 shows the different subtypes of AMD identified. In 26% of cases it was not possible to identify a subtype. In 34% neovascular AMD was identified, and in 40% geographic atrophy/ late-stage AMD was identified. Table 3 shows the age-specific prevalence rates of AMD causing visual impairment. Overall, 3.7% (95% CI, 3.2%– 4.2%) of our sample of people 75 years or older were visually impaired due to AMD. There was a higher rate in women (4.4%) than in men (2.6%) (design-based 2 ⫽ 48.1, P⬍0.0001). There was a strong relationship with age: 1.1% of the 75- to 79-year-old age group were visually impaired due to AMD, compared with 14.4% of people 90 years or older (design-based 2 ⫽ 143.9, P⬍0.0001). Women had a higher rate than men at all ages. The odds ratio (OR) of AMD causing visual impairment in women versus men, controlled for age, was 1.44 (95% CI, 1.22–1.69). Applying these figures to the United Kingdom population in 2001,14 there are estimated to be 192 000 people 75 years or older visually impaired due to AMD (144 000 –239 000) living in the United Kingdom. Of these, 146 000 (76%) are women. These age-specific prevalence rates are calculated assuming that the prevalence of visual impairment in the 31% of people who did not attend the examination was similar to that of those who attended and had vision measured. There was also a group of people who were known to be visually impaired but for whom no cause of visual loss was established. We have calculated the prevalence rates assuming that none of these people had visual loss due to AMD. This gives a conservative measure of prevalence. Table 3 also shows the prevalence recalculated excluding people with an unknown cause of visual loss from the denominator. This suggests that the prevalence of AMD in people with an unknown cause of visual loss is similar to that in people with a known cause. This results in a less conservative estimate of the prevalence of AMD causing visual impairment. These figures indicate that as many as 1 in 5 women 90 years or older may be visually impaired due to AMD. Table 4 shows the prevalence of AMD causing severe visual impairment (binocular acuity less than 6/60). The overall prevalence in people 75 years or older was 1.6% (95% CI, 1.3%–1.9%). As for AMD causing visual impairment, the prevalence increased sharply with increasing age. At ages 90 and above, the prevalence was 6.6% (95% CI, 4.8%– 8.4%). Women had a higher rate at all ages. The OR of AMD causing severe visual impairment in women versus men, controlled for age, was 1.40 (95% CI, 1.04 –1.89).
Discussion We estimate that 3.7% (95% CI, 3.2%– 4.2%) of the population 75 years or older has AMD causing visual impairment. The prevalence increases rapidly with increasing age—14.4% (11.6%–17.2%) of the population 90 years or older are visually impaired due to AMD. Applying the age-specific prevalence rates to the United Kingdom population gives an estimated 192 000 people 75 years or older
Total no. of visually impaired people with definite AMD identified as a cause of visual loss Type unspecified Neovascular AMD Geographic atrophy/late-stage AMD
428 112 144 172
% 100 26.2 33.6 40.2
visually impaired due to AMD in the United Kingdom (95% CIs, 144 000 –239 000). The MRC Trial of the Assessment and Management of Older People in the Community was a large populationbased trial, recruiting participants 75 years or older from general practices selected to be representative of the British population. The size of the study enabled us to identify a large group of people visually impaired due to AMD. However, the size and geographical spread of practices, combined with the age of the participants, meant that we were unable to arrange for a standardized ophthalmic examination of everyone identified as visually impaired during the trial. People who were newly identified as visually impaired were referred to the hospital eye service. Using a combination of medical record review in the general practice and a hospital ophthalmologist questionnaire, we were able to establish the cause of visual loss in 76% of people with a pinhole-corrected acuity of less than 6/18 in the better eye. We had good agreement at the hospital and general practice level. However, our method of case ascertainment must be considered less robust than a cross-sectional survey using standardized methods. In a recent review pooling data from several international studies of AMD, prevalences of visual impairment due to AMD were estimated as 1.6% (75–79 years), 3.6% (80 – 84), 8.1% (85– 89), and 15.3% (ⱖ90).5 These results compare well with the estimates of prevalence from the current study: 1.1%, 3.6%, 8.1%, and 14.4%. Owen et al estimated that there are currently 214 000 (151 000 –310 000) with visual impairment caused by AMD (visual acuity of 6/18 or worse).5 This is slightly higher than the estimate from this study (192 000 [95% CI, 144 000 –239 000]). However, reflecting the relatively large number of cases in the current study, our CIs are substantially narrower. If we adjust for missing data in our study, we estimate somewhat higher prevalence rates. However, we are then making various assumptions about the nature of the people for whom a cause of visual loss was not available. These people were less likely to be blind than people for whom the cause of visual loss was available. It may well be that they were not as affected by AMD. There are several reasons why this study will have underestimated the burden of AMD in this age group: 1. As the MRC Trial was a pragmatic assessment of simple assessment methods in general practice, the cutoff for referral was less than 6/18. When assessing the cause of visual impairment, we were restricted to this cutoff as well. This means that we are likely to
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Ophthalmology Volume 111, Number 3, March 2004 Table 3. Age-Specific Prevalence of Age-Related Macular Degeneration Causing Binocular Visual Impairment of Less than 6/18 Prevalence Excluding People with No Information on Cause of Visual Impairment from Denominator
Minimum Prevalence
All ages Total Men Women Men and women 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs Men 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs Women 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs
N
% Prevalence
SE
95% CI
N
% Prevalence
SE
95% CI
13 900 5357 8543
3.7 2.6 4.4
0.245 0.247 0.286
3.2–4.2 2.1–3.1 3.8–5.0
13 584 5269 8315
3.8 2.6 4.6
0.252 0.250 0.296
3.3–4.3 2.1–3.1 4.0–5.1
6582 4388 2186 744
1.1 3.6 8.1 14.4
0.130 0.325 0.825 1.395
0.9–1.4 3.0–4.3 6.4–9.7 11.6–17.2
6516 4305 2098 665
1.1 3.7 8.4 16.1
0.132 0.334 0.862 1.603
0.9–1.4 3.0–4.4 6.7–10.1 12.9–19.3
2831 1623 729 174
0.9 2.9 6.2 11.5
0.187 0.360 0.885 2.287
0.5–1.3 2.2–3.6 4.4–8.0 6.9–16.1
2808 1598 704 159
0.9 2.9 6.4 12.6
0.188 0.366 0.906 2.526
0.5–1.3 2.2–3.7 4.6–8.2 7.5–17.7
3751 2765 1457 570
1.3 4.1 9.0 15.3
0.191 0.435 0.994 1.646
0.9–1.7 3.2–4.9 7.0–11.0 12.0–18.6
3708 2707 1394 506
1.3 4.1 9.4 17.2
0.193 0.450 1.040 1.892
0.9–1.7 3.2–5.0 7.3–11.5 13.4–21.0
CI ⫽ confidence interval; SE ⫽ standard error.
have underestimated the impact of AMD, as many people will be visually impaired to lesser levels. A visual acuity of less than 6/12 but greater than 6/18 will have many disadvantages—for example, inability to drive. 2. The MRC Trial did not include people in long-term nursing care. Other studies have shown a high prevalence of visual impairment in nursing homes. For example, in people 85 years or older taking part in the National Diet and Nutrition Study, 30% of those
living in the community were visually impaired (less than 6/18), compared with 47% of those living in residential nursing homes.15 Our results, from the largest and most representative study of the causes of vision loss in older people in the British population, indicate that nearly 200 000 people 75 years or older are visually impaired due to AMD in the United Kingdom. As the population ages, this figure will rise. The needs of this group for vision aids and other
Table 4. Age-Specific Prevalence of Age-Related Macular Degeneration Causing Binocular Visual Impairment of Less than 6/60
All ages Total Men Women Men and Women 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs Men 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs Women 75–79 yrs 80–84 yrs 85–89 yrs ⱖ90 yrs
N
% Prevalence
SE
95% CI
13 900 5357 8543
1.6 1.1 1.9
0.141 0.152 0.175
1.3–1.9 0.8–1.4 1.5–2.2
6582 4388 2186 744
0.3 1.7 3.2 6.6
0.069 0.207 0.473 0.879
0.2–0.5 1.3–2.1 2.3–4.2 4.8–8.4
2831 1623 729 174
0.2 1.5 2.1 6.3
0.082 0.281 0.501 1.767
0.1–0.4 1.0–2.1 1.0–3.1 2.8–9.9
3751 2765 1457 570
0.4 1.8 3.8 6.7
0.100 0.267 0.610 0.898
0.2–0.6 1.3–2.4 2.6–5.1 4.9–8.5
CI ⫽ confidence interval; SE ⫽ standard error.
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Evans et al 䡠 AMD Causing Visual Impairment in Older People in Britain support in the community should be addressed; research on the causes of AMD and possible preventive measures should be given priority.
7.
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