Epidemiology of sight loss in the UK Astrid Fletcher London School of Hygiene & Tropical Medicine.
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Transcript of Epidemiology of sight loss in the UK Astrid Fletcher London School of Hygiene & Tropical Medicine.
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Epidemiology of sight loss in the UK
Astrid Fletcher
London School of Hygiene & Tropical Medicine
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Overview
• What do we know about the prevalence of sight loss in the UK
• What are the major conditions leading to sight loss?
• Do we need more research?• What are the gaps in knowledge? • What are the main research questions
arising from the data on prevalence and causes?
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Use of prevalence data
• Prevalence defined as proportion of people with sight loss at a specific time point
• Describes the relative importance of a health problem in the population
• Usually reported for different age groups• Prevalence rates applied to age specific
population data provide estimates of number of people affected
• Knowledge of prevalence and numbers by causes of sight loss is important for planning services and identifying unmet need
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Prevalence estimates of sight loss are only the first step
Largely uninformative without data on the underlying conditions leading to sight loss
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Approaches to measurement and categorisation of sight loss
• Vision difficultiesSelf report of difficulties with vision related functions ranging from single item questions to disability scales
• Vision related quality of life scales Describe the impact of vision problems on
everyday functioning and well-being • Clinical measures
“Objective” measures eg Distance and near acuity, visual fields etc
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Definition of visual impairment
• WHO cut-points are based on best eye and after full refraction– Visual impairment <6/18 – Low vision <6/18 to 3/60 – Blindness <3/60
• Definitions used in UK studies – <6/12 (approximates to UK driving requirement)– <6/18 & <3/60– Presenting or pinhole corrected or after refraction
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Prevalence of best-corrected visual acuity <6/12 in population-based studies
Congdon et al Arch Ophthalmol 1998
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Surveys of adult population in the UK using visual acuity measurements
Survey
Setting
Age Number
Response
Lavery 1988 Melton
Mowbray GP
76+ 529
78%
Wormald 1992
Inner London GP
65+ 207 72%
Reidy 1998 N. London
17 GP practices
65+ 1547 84%
National Diet & Nutrition Study 2000
Postcode sampling
& Sample of nursing
homes
65+ 1,362
75% private households
94% nursing homes
MRC Assessment trial 2002
53 GPs across GB
75+ 14,600 69%
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Prevalence of VI and blindness
0
5
10
15
20
25
30
35
40
45
Age
Pre
vale
nce VI M
VI F
Blind M
Blind F
MRC Assessment Trial Prevalence of binocular visual impairment
(<6/18) and blindness (<3/60)
74-79 80-84 85-89 90+
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Study Age V.I. N %<6/18
%<6/12
Lavery 76+ Refraction 474 26.2 -
Wormald 75+ Refraction 106 14.2 21.8
North London 65+ Presentingbilateral
1547 - 30.2
NDNS 75+ Pinhole 1362 15.2 32.4
MRC 75+ Presentingbinocular
14600 12.410.8-13.9
20.117.8-22.0
UK studies: prevalence visual acuity
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Study Age V.I. N %<6/18
NDNS 75+ Pinhole 1362 15.2
MRC 75+ Presentingbinocular
14600 12.410.8-13.9
Rotterdam 75+ Refraction 1806 4.7
Baltimore 70+ Refraction 836 4.8
Beaver Dam 75+ Refraction 795 6.0
Blue Mountains
70+ Refraction 783 5.0
Melbourne 70+ Refraction 605 6.2
Comparison with other non UK studies: VA <6/18 in 75+
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Variation in estimates between studies
• Definitions• Measurement quality • Age structure
– especially in oldest age groups where prevalence is highest
• Sampling error – Small numbers in older age groups
May be “true” differences between populations
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What is the significance of differences in prevalence between
populations?
• Variations in prevalence reflect variation in the prevalence of underlying conditions– Availability and use of eye care services– Aetiology of specific eye problems in
different populations
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Comparison between UK and non UK studies
• Most non UK studies use only best corrected visual acuity
• Exclude data on vision impairment due to refractive error
• Presenting vision is the most appropriate measure of a person’s everyday vision
• Recommended by WHO in 2003 that presenting VA <6/18 be used as the main definition of visual impairment
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MRC TrialCauses of visual impairment (VA
<6/18) aged 75+
31.6
32.6
20.46.4
2.1
2.6
3.8
Refractive error
AMD
Cataract
Glaucoma
Diabetic eyedisease
Myopic deg
OtherPrevalence of VA <6/18 excluding RE = 8%
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Comparison with other studies – blindness (VA <3/60)
0%
20%
40%
60%
80%
100%
Other
Diabetes
Glaucoma
Cataract
AMD
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Comparison with other studies - low vision (VA <6/18-3/60)
0%
20%
40%
60%
80%
100%
Other
Diabetes
Glaucoma
Cataract
AMD
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Visual impairment in older people
50% to 70% of visual impairment in the older age group is due to “remediable” causes and could be improved by:
specs/ new specs
cataract surgery
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Visual impairment in older people
Often not known to health services
Of people aged >65 (Reidy et al 1999):• only 12% of people with cataract were in touch with eye services• only one third of those with uncorrected refractive error had seen an optician in the past 12 months
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MRC assessment trial
• Of people eligible for referral to an ophthalmologist around a half were referred by the GP
• Among those referred, 88% attended• Over 80% of people advised to see an
optician did so• New lenses were obtained by 45%• The main reasons given for not obtaining
glasses were ‘not needed’ and cost
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Should new evidence on prevalence and causes of vision
impairment be a research priority?
• Probably not for the older age group. Evidence is reasonably consistent with other developed countries
• Lack information on ethnic minorities in whom prevalence of VI, underlying causes and eye care use may be different from the majority population
• Evaluation of strategies to reduce the high proportion of untreated remediable conditions should be priority for action