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Epidemiology of sight loss in the UK
Astrid Fletcher
London School of Hygiene & Tropical Medicine
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?
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
Prevalence estimates of sight loss are only the first step
Largely uninformative without data on the underlying conditions leading to sight loss
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
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
Prevalence of best-corrected visual acuity <6/12 in population-based studies
Congdon et al Arch Ophthalmol 1998
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%
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+
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
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+
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
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
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
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%
Comparison with other studies – blindness (VA <3/60)
0%
20%
40%
60%
80%
100%
Other
Diabetes
Glaucoma
Cataract
AMD
Comparison with other studies - low vision (VA <6/18-3/60)
0%
20%
40%
60%
80%
100%
Other
Diabetes
Glaucoma
Cataract
AMD
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
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
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
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