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Prevalence of vision impairment and blindness

    Contents

    2.1 Population data
    2.2 Prevalence sources
    2.3 Blindness
    2.4 Mild and moderate vision impairment
    2.5 Total population with vision impairment and blindness

    Summary

    The prevalence of blindness in the ROI was estimated using NCBI register data (of people registered as blind) and from this, the prevalence of mild and moderate vision impairment was imputed using ratios from a study on vision impairment in the UK.

    Overall, it is estimated that in the ROI in 2010, there were:

    • 12,995 blind people;
    • 157,156 people with mild vision impairment;
    • 54,681 people with moderate vision impairment; and
    • 224,832 people with total (mild and moderate) vision impairment and blindness.

    Total vision impairment and blindness is projected to grow to 271,996 people by 2020, including 187,928 people with mild vision impairment, 66,070 people with moderate vision impairment and 17,997 blind people.

    The burden of disease methodology in this study is based on a prevalence approach to cost measurement, as the data sources lend themselves to such an approach. Prevalence approaches measure the number of people with a given condition (in this case mild VI, moderate VI, or blindness) in a base period (in this case calendar year 2010) and the costs of treating them, as well as other financial and non-financial costs (productivity losses, carer burden, loss of quality of life) in that year, due to the condition. When the aim of a study is to estimate the economic burden of a disease during a specified period of time (e.g. one year) a prevalence approach is recommended. If the aim is to illustrate the economic consequences of various interventions, an incidence approach is preferable (Wimo et al, 2006).

    One advantage of a prevalence approach is that where results are reported for a series of years, trends in the disease burden can be examined. This method also avoids the uncertainty surrounding estimates of future treatment costs associated with an incidence approach. It is recognised that given the chronic nature of VI some of the total prevalence of VI in each year may include the same individuals. However, to calculate the burden of disease using a prevalence based approach all that is required are prevalence rates for the population of interest and average annual costs per person with VI.

    In this study, the prevalent numbers of people with mild VI, moderate VI, and blindness in the ROI were calculated by multiplying national population data by estimated prevalence rates according to VI severity and age-gender group. An overview of the method used to project population prevalence to the year 2020 is provided below.

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