1. Epidemiology of sight loss in the UK
Astrid Fletcher
London School of Hygiene
& Tropical Medicine

2. 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?

3. 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

4. Prevalence estimates of sight loss are only the first step
Largely uninformative without data on the underlying conditions leading to sight loss

5. Approaches to measurement and categorisation of sight loss
Vision difficulties
Self 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

6. 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

7. Prevalence of best-corrected visual acuity <6/12 in population-based studies
Congdon et al Arch Ophthalmol 1998

8. Surveys of adult population in the UK using visual acuity measurements

9. MRC Assessment Trial Prevalence of binocular visual impairment (<6/18) and blindness (<3/60)
74-79
80-84
85-89
90+

10. UK studies: prevalence visual acuity
Study
Age
V.I. N %
<6/18
<6/12
Lavery
76+
Refraction
474
26.2 -
Wormald
75+
106
14.2
21.8
North London
65+
Presenting
bilateral
1547
30.2
NDNS
Pinhole
1362
15.2
32.4
MRC
binocular
14600
12.4
20.1

11. Comparison with other non UK studies: VA <6/18 in 75+
Study
Age
V.I. N %
<6/18
NDNS
75+
Pinhole
1362
15.2
MRC
Presentingbinocular
14600
12.4
Rotterdam
Refraction
1806
4.7
Baltimore
70+
836
4.8
Beaver Dam
795
6.0
Blue Mountains
783
5.0
Melbourne
605
6.2

12. 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

13. 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

14. 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

15. MRC Trial Causes of visual impairment (VA <6/18) aged 75+
Prevalence of VA <6/18 excluding RE = 8%

16. Comparison with other studies – blindness (VA <3/60)

17. Comparison with other studies - low vision (VA <6/18-3/60)

18. 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

19. 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

20. 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

21. 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