Blindness was defined as visual acuity of worse than 3/60 in the better eye and severe visual impairment (SVI) was defined as visual acuity of worse than 6/60 but 3/60 or better in the better eye.
Operated cataract was defined as the presence of pseudophakia (implanted IOL) or aphakia (no IOL) on internal eye examination.
Visual acuity assessment commonly includes measurement of presenting visual acuity (i.e. with spectacles if normally worn) as well as pinhole acuity. The use of a pinhole corrects vision loss that is due to refractive error, which can be corrected by spectacles. In RAAB surveys pinhole acuity is used to identify operable cataract when pinhole acuity remains poor in the presence of an opaque lens. In many low and middle income countries, as in high income countries, cataract surgery is now often offered before someone becomes blind. Therefore, in this analysis, operable cataract was defined as pinhole visual acuity of SVI or blindness (less than 6/60) where the principal cause was cataract. The analysis can be repeated using other visual acuity cut-offs for operable cataract as appropriate (e.g. <3/60, < 6/18).
Cataract surgical coverage (CSC) was defined as the number of people in a defined population with operated cataract as a proportion of those having operable plus operated cataract[25 ] (i.e. pinhole visual acuity worse than 6/60; CSCpersons <6/60).
where
Effective cataract surgical coverage (eCSC) measures the number of people in a defined population with operated cataract and a good outcome (i.e. presenting vision 6/18 or better) as a proportion of those having operable plus operated cataract. As for CSC, eCSC was calculated using the cut-off for operable cataract of worse than 6/60 pinhole visual acuity (eCSCpersons <6/60).
where
Operated cataract was defined as the presence of pseudophakia (implanted IOL) or aphakia (no IOL) on internal eye examination.
Visual acuity assessment commonly includes measurement of presenting visual acuity (i.e. with spectacles if normally worn) as well as pinhole acuity. The use of a pinhole corrects vision loss that is due to refractive error, which can be corrected by spectacles. In RAAB surveys pinhole acuity is used to identify operable cataract when pinhole acuity remains poor in the presence of an opaque lens. In many low and middle income countries, as in high income countries, cataract surgery is now often offered before someone becomes blind. Therefore, in this analysis, operable cataract was defined as pinhole visual acuity of SVI or blindness (less than 6/60) where the principal cause was cataract. The analysis can be repeated using other visual acuity cut-offs for operable cataract as appropriate (e.g. <3/60, < 6/18).
Cataract surgical coverage (CSC) was defined as the number of people in a defined population with operated cataract as a proportion of those having operable plus operated cataract[25 ] (i.e. pinhole visual acuity worse than 6/60; CSCpersons <6/60).
where
x = individuals with unilateral pseudo/aphakia (i.e. operated cataract) and operable cataract in the other eye;
y = individuals with bilateral pseudo/aphakia, regardless of visual acuity;
z = individuals with bilateral operable cataract.
Effective cataract surgical coverage (eCSC) measures the number of people in a defined population with operated cataract and a good outcome (i.e. presenting vision 6/18 or better) as a proportion of those having operable plus operated cataract. As for CSC, eCSC was calculated using the cut-off for operable cataract of worse than 6/60 pinhole visual acuity (eCSCpersons <6/60).
where
a = individuals with unilateral pseudo/aphakia achieving presenting visual acuity of 6/18 or better in the operated eye and operable cataract in the other eye;
b = individuals with bilateral pseudo/aphakia achieving presenting visual acuity of 6/18 or better in at least one eye;
x, y and z as above for CSC.
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