Table 4.

Comparison of sampling techniques and the prevalence rates of refractive errors in different populations from previously published studies.

Epidemiological Study	Sampling Technique	Age Group (Years)	Myopia (%)	Hyperopia (%)	Astigmatism (%)	Anisometropia (%)
The Beaver Dam Eye Study (USA) [22] †	a door to door census	≥43	26.2	49.0	NA	NA
The Blue Mountains Eye Study (Australia) [20] †	a door to door census	≥49	15.5	56.6	NA	NA
The Tajimi Study (Japan) [15] †	random sampling	≥40	41.8	27.9	54.0	15.1
The Gutenberg Health Study (Germany) [7] †	random sampling	≥35	35.1	32.8	32.3	13.5
The Barbados Eye Study (Barbados) [9] †	random sampling	≥40	21.9	46.9	NA	NA
The Singapore Indian Eye Study (Singapore) [12] †	age-stratified random sampling	≥40	28.0	35.9	54.9	9.8
The Segovia Study (Spain) [11] ‡	age-stratified random sampling	≥40	25.4	43.6	53.5	12.3
The Yazd Eye Study (Iran) [18] ‡	multistage random cluster sampling	≥40	36.5	20.6	53.8	11.9
Korean National Health and Nutrition Examination Survey (South Korea) [19] §	multistage stratified cluster random sampling	≥20	48.1	24.2	34.0	NA
The Nigerian National Blindness and Visual Impairment Study (Nigeria) [33] †	multistage stratified cluster random sampling	≥40	16.2	50.7	63.5	NA
The National Blindness and Low Vision Survey of Bangladesh (Bangladesh) [34] †	cluster sampling and a door to door enumeration	≥30	22.1	20.6	32.4	7.5
The Shihpai Eye Study (Taiwan) [17] †	random sampling and a door to door enumeration	≥65	19.4	59.0	74.0	21.8

† Myopia (<−0.5 D), Hyperopia (>+0.5 D), Astigmatism (>0.5 cyl D), Anisometropia (>1.0 D). ‡ Myopia (<−0.5 D), Hyperopia (>+0.5 D), Astigmatism (>0.5 cyl D), Anisometropia (≥1.0 D). § Myopia (<−0.5 D), Hyperopia (>+0.5 D), Astigmatism (>1.0 cyl D).