Epidemiology and Demographics of Visual Impairment Flashcards
What is visual impairment:
- Reduced binocular visual acuity, which cannot be improved even with best optical correction provided by conventional lenses
- Conventional lenses include the required distance correction and near vision additions up to +4DS
What is epidemiology:
- The study of the distribution, determinants and control of disease in human populations
- In order to set policies and priorities and to evaluate global eye health
What is prevalence:
- Measure of disease frequency
- Number of people with a disease at a given time
- Typically expressed in terms of a proportion (usually %)
Equation for prevalence:
Prevalence = No. of cases or events / Total population at risk
What is incidence:
- Number of cases occurring in a specified time
- Sometimes expressed as a rate: the number of new cases occurring over a given time frame in relation to the total number of persons at risk during the same time frame
Equation for incidence:
Incidence = No. of new cases over a given time interval / Total population at risk at the beginning of the specified time
Visually impaired statistic:
Of the 253 million people in the world who are visually impaired
* 55% are women (139 million).
* Approx. 203 million, representing 80%, are aged 50 years or older.
Global causes of Blindness and MSVI (all ages)
- Cataract: 25.8%
- Refractive Error: 48.99% - most common cause of VI – easily corrected by glasses
- Glaucoma:2.78%
- Age Related Macular Degeneration: 4.10%
- Corneal Opacities:1.65%
- Diabetic Retinopathy: 1.16%
- Trachoma:0.79%
- Other: 14.71%
Change in prevalence of visual impairment from 1990 to 2015:
- Decline observed in prevalence of visual impairment for most eye conditions except Diabetic Retinopathy and the ‘Other’ category.
- Related to increase in the prevalence of diabetes CAUSING INCREASE IN VI
Global Incidence of Visual Impairment:
- Incidence varies with age
- Not many studies
- Priverno Eye Study (Cedrone et al, 2003)
- Blindness 0.1%
- Low Vision 1.3%
Risk Factors for Sight loss in the UK:
- Old Age
- 31 per cent aged 85 years and over
- Low Income
- Diabetes
- Smoking
- Learning Disabilities
- Ethnic Minority Groups
- Other health conditions E.G HTN
Prevalence of Visual Impairment in the UK:
- 149,938 people: SSI register (England & Wales) (2017)
- 157,531 people: SI register (England & Wales) (2017
- Registration is voluntary so not everyone who has VI will appear on these registers so data is underestimating number of people with VI 2 million VI across UK
UK Incidence of Visual Impairment:
- Incidence varies with age
- 20605 new registrations on the SI and SSI register(2016/17)
Prevalence of childhood VI in the UK:
- Approx. 12,000 SI and SSI children between the ages of 0–16
- Around half have additional disabilities and/or special educational needs
- SSI Register (2017)
- 0- 4 years: 637 children
- 5-17 years: 4,651 children
- SI Register (2017)
- 0- 4 years: 604 children
- 5-17 years: 5675 children
Incidence of childhood blindness in the UK: New registrations:
- SSI register (2017)
- 0- 4 years: 200 children
- 5-17 years: 205 children
- SI Register (2017)
- 0- 4 years: 175children
- 5-17 years: 310 children
