- Blindness: Visual acuity <3/60 in the better eye
- Vision Impairment: Moderate & Severe Visual Impairment with visual acuity >6/18 to ≥3/60
- Prevalence: The age-standardised prevalence as a percentage of a population that is affected with vision impairment or blindness
- Population Affected: Calculated based upon the total population and the crude prevalence rate
How to use the maps
The GVD dataset provides several data-points to access. Our new map designs let you toggle between the following aspects:
Selecting either ‘Blind’ or ‘Vision Impaired’ on the navigation panel (to the right) toggles between these two conditions. At the bottom of the navigation panel is a key matching the intensity of colour with prevalence of the condition (lighter is lower, darker is higher prevalence). This gives us a global perspective on prevalence. Running your mouse over each country, or tapping on a touchscreen, will give you the name of the country, the prevalence rate, the country’s population and the population affected – as at the date for the year you select at the top; as the GVD dataset has been prepared for different years (1990-2010), the mouseover or tap shows you the year under consideration. The percentage given is the age-standardised prevalence which accounts for the difference in age structure between populations.
The ‘population affected’ figure represents the number of people according to the condition, sex, age, and year that you selected. This figure multiplies the ‘crude prevalence’ (not age-standardised) by number of population, to give the number of population affected by vision impairment or blindness.
NB: One of the key aspects of the GVD dataset is the ability to compare prevalence of changes over time. You will note that, by default, the data is set to ‘2010’. You can run the time-lapse feature or toggle the years by clicking the year at the top to take you back in time.
Once you have chosen the condition, you can now choose to look at prevalence in men, women or both sexes combined. This is also a powerful aspect, hitherto unavailable with existing datasets. We now know, for example, that women represent 60% of blindness and 57% of vision impairment. Again, you get country-wise information by running your mouse over, or tapping, each country.
NB: Again, note the time aspect as you toggle through these options.
The GBD dataset allows us to look at two separate age categories – all ages and those aged 50 years and older. This becomes helpful because older populations account for a higher proportion of vision impairment and blindness. By running the mouse over, or tapping on, each country these variations stand out.
NB: The ‘population’ figure on mouseover/tap refers to the total population by age category. For example, the total population of France is 62 million (all ages) and 22.6 million (adults aged 50 years and older).
The prevalence of both blindness and vision impairment have been in decline over the past couple of decades. The timelapse option, from 1990-2010, (click the play button at the top left) makes this evident in a powerful and graphical manner.