Table 2. Empirical literature reporting productivity and welfare impacts of visual impairment identified in the systematic review.
| Study | Study design, site; year of implementation | Intervention description | Study population and sample size | Outcome for use in benefit-cost analysis | Risk of bias assessmenta |
|---|---|---|---|---|---|
| Kuper et al., 200853 | Population-based case-control study Nakuru district, Kenya; 2005–2006 |
Cases: Cataract surgery (implied) Control: No intervention |
Cases: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye Control: Age and gender matched individuals without visual impairment Cases: n = 142 Control: n = 75 |
Cases had lower monthly per capita expenditure (US$ 24) compared to controls (US $30) | Serious risk |
| Kuper et al., 200853 | Population-based case-control study Satkhira district, Bangladesh; 2005–2006 |
Cases: Cataract surgery (implied) Control: No intervention |
Cases: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye Control: Age and gender matched individuals without visual impairment Cases: n = 216 Control: n = 279 |
Cases had lower monthly per capita expenditure (US$ 18) compared to controls (US$ 25) | Serious risk |
| Kuper et al., 200853 | Population-based case-control study Negros Island and Panay Islay, Philippines; 2005–2006 |
Cases: Cataract surgery (implied) Control: No intervention |
Cases: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye Control: Age and gender matched individuals without visual impairment in the same cluster Cases: n = 238 Control: n = 180 |
Cases had lower monthly per capita expenditure (US$ 23) compared to controls (US$ 30) | Serious risk |
| Polack et al., 200846 | Population-based case-control study Nakuru district, Kenya; 2005–2006 |
Cases: Cataract surgery (implied) Control: No intervention |
Cases: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye (n = 139) Control: Age and gender matched individuals without visual impairment (n = 124) |
Cases: Maximum 14% (3.4/24 hours) of time spent on productive activities;b 27% (38/139 people) require assistance in activities Controls: 24% (5.8/24 hours) of time spent on productive activities;b 3% (4/124 people) require assistance in activities |
Serious risk |
| Polack et al., 200846 | Population-based case-control study Satkhira district, Bangladesh; 2005–2006 |
Cases: Cataract surgery (implied) Control: No intervention |
Cases: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye (n = 217) Control: Age and gender matched individuals without visual impairment (n = 280) |
Cases: Maximum 13% (3.1/24 hours) of time spent on productive activities;b 47% (102/217 people) require assistance in activities. Controls: 21% (5/24 hours) of time spent on productive activities;b 9% (25/278 people) require assistance in activities |
Serious risk |
| Polack et al., 200846 | Population-based case-control study Negros Island and Panay Islay, Philippines; 2005–2006 |
Cases: Cataract surgery (implied) Control: No intervention |
Cases: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye (n = 238) Control: Age and gender matched individual(s) without visual impairment (n = 163) |
Cases: Maximum 19% (4.6/24 hours) of time spent on productive activities;b 22% (52/238 people) require assistance in activities. Controls: 25% (6/24 hours) of time spent on productive activities;b 9% (15/163 people) require assistance in activities |
Serious risk |
| Kuper et al., 201044 | Prospective cohort study with matched controls Nakuru district, Kenya; 2006 |
Exposed: Provision of free cataract surgery and transport to hospital Unexposed: No intervention |
Exposed: Individuals with cataract aged ≥ 50 years with pinhole visual acuity < 6/24 in the better eye (n = 65) Unexposed: Age and gender matched individuals without visual impairment (n = 56) |
After one year, per capita monthly household expenditure had increased from US$ 22 to US$ 30 in the exposed group and had increased from US$ 35 to US 36 in the unexposed group | Serious risk |
| Kuper et al., 201044 | Prospective cohort study with matched controls Satkhira district, Bangladesh; 2005–2006 |
Exposed: Provision of free cataract surgery and transport to hospital Unexposed: No intervention |
Exposed: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye (n = 99) Unexposed: Age and gender matched individual(s) without visual impairment (n = 222) |
After one year, per capita monthly household expenditure had increased from US$ 16 to US$ 23 in exposed group and had decreased from US$ 24 to US$ 23 in unexposed group | Serious risk |
| Kuper et al., 201044 | Prospective cohort study with matched controls Negros Island and Panay Islay, Philippines; 2005–2006 |
Exposed: Provision of subsidized cataract surgery and reimbursed transport costs Unexposed: No intervention |
Exposed: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye (n = 99) Unexposed: Age and gender matched individuals without visual impairment (n = 152) |
After one year, per capita monthly household expenditure had increased from US$ 24 to US$ 45 in the exposed group and had increased from US$ 32 to US$ 36 in the unexposed group | Serious risk |
| Polack et al., 201045 | Prospective cohort study with matched controls Nakuru district, Kenya; 2006 |
Exposed: Provision of free cataract surgery and transport Unexposed: No intervention |
Exposed: Individuals with cataract aged ≥ 50 years with pinhole visual acuity < 6/24 in the better eye (n = 139) Unexposed: Age and gender matched individual(s) without visual impairment (n = 124) |
After one year: 1 hour and 5 minutes more time spent on productive activities per day; Decrease in percentage of cases requiring assistance with activities from 25% to 12% | Serious risk |
| Polack et al., 201045 | Prospective cohort study with matched controls Satkhira district, Bangladesh; 2005–2006 |
Exposed: Provision of free cataract surgery and transport to hospital Unexposed: No intervention |
Exposed: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye (n = 217) Unexposed: Age and gender matched individual(s) without visual impairment (n = 280) |
After one year: 1 hour and 20 minutes more time spent on productive activities per day; Decrease in percentage of cases requiring assistance with activities from 43% to 19% | Serious risk |
| Polack et al., 201045 | Prospective cohort study with matched controls Negros Island and Panay Islay, Philippines; 2005–2006 |
Exposed: Provision of subsidized cataract surgery and reimbursed transport costs Unexposed: No intervention |
Exposed: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye (n = 238) Unexposed: Age and gender matched individual(s) without visual impairment (n = 163) |
After one year: 1 hour and 51 minutes more time spent on productive activities per day; Decrease in percentage of cases requiring assistance with activities from 23% to 1% | Serious risk |
| Finger et al., 201234 | Prospective cohort study, no control group Tamil Nadu, India; 2009–2010 |
Free cataract surgery and transport | Individuals with cataract (visual acuity < 6/60), aged ≥ 40 years, classified as poor and without prior cataract surgery; n = 294 | After one year, average monthly household income had increased by 531 Indian rupees | Serious risk |
| Hannum & Zhang, 201248 | Cross-sectional survey of eyeglasses wearers with propensity score matched controls Gansu, China; 2004 |
Provision of eyeglasses to those with visual impairment (implied) | Junior high school students aged 13–16 years; Wearing spectacles: n = 94 (literacy test) or n = 106 (math and language test) Non-wearers: n = 1398 (literacy test) or n = 1450 (math and language test) |
Treatment effect on the treated: Those wearing glasses had higher academic achievement, 0.34 SD improvement in literacy test scores; 0.26 SD improvement in math test scores and 0.13 SD improvement in language test scores | Moderate risk |
| Danquah et al., 201449 | Prospective cohort study with matched controls Satkhira district, Bangladesh; 2005–2006 |
Exposed: Provision of free cataract surgery and transport to hospital Unexposed: No intervention |
Exposed: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye; (n = 56) Unexposed: Age and gender matched individuals without visual impairment; (n = 142) |
After 6 years, per capita monthly household expenditure had increased from US$ 14.95 to US$ 23.29 in exposed group and had decreased from US$ 26.90 to US$ 24.29 in unexposed group | Serious risk |
| Danquah et al., 201449 | Prospective cohort study with matched controls Negros Island and Panay Islay, Philippines; 2005–2006 |
Exposed: Provision of subsidized cataract surgery and reimbursed transport costs to hospital Unexposed: No intervention |
Exposed: Individuals with cataract aged ≥ 50 years with pinhole corrected visual acuity < 6/24 in the better eye; (n = 51) Unexposed: Age and gender matched individuals without visual impairment; (n = 91) |
After 6 years, per capita monthly household expenditure had increased from US$ 21.73 to US$ 38.90 in exposed group and had increased from US$ 29.01 to US$ 37.40 in unexposed group | Serious risk |
| Essue et al., 201450 | Prospective cohort study, no control group; Hue, Binh Dinh, Vinh Long, and Thai Binh provinces, Viet Nam; 2011 |
Free cataract surgery | Individuals with cataract aged ≥ 18 years with a visual acuity ≥ 6/18 in the better eye; n = 381 | After one year, the annual household income had increased by US$ 271 (51% increase) | Serious risk |
| Joseph, 201457 | Prospective cohort study with control group Thiruvananthapuram district, Kerala, India; No year reported |
Exposed: Provision of free corrective eyeglasses for students with myopia Unexposed: Students without myopia |
Rural and urban primary school students; Exposed n = 185 Unexposed: equated group; no other information reported |
After five months, total test scores had increased from 20.5 to 27.1 in exposed group and from 26.4 to 27.5 in unexposed group | Serious risk |
| Ma et al., 201412 | Cluster RCT Tianshui prefecture, Gansu province and Yulin prefecture, Shaanxi province, China; 2012 |
Treatment: Provision of free eyeglasses following eye examination Control: Prescription for eyeglasses sent to parents with free eyeglasses provided at endline |
Students at rural primary schools in grades 4–5 with uncorrected visual acuity of ≤ 6/12 in either eye Treatment: n = 1153 Control: n = 1036 |
After one school year, the intervention group had higher academic achievement, 0.11 SD improvement in test scores relative to the control group | Low risk |
| Ma et al., 201412 | Cluster RCT Tianshui prefecture, Gansu province and Yulin prefecture, Shaanxi province, China; 2012 |
Treatment: provision of vouchers for eyeglasses Control: Prescription for eyeglasses sent to parents with free eyeglasses provided at endline |
Students at rural primary schools in grades 4–5 with uncorrected visual acuity of ≤ 6/12 in either eye Treatment: n = 988 Control: n = 1036 |
After one school year, the intervention group had non-significant increase in academic achievement, 0.04 SD improvement in test scores relative to the control group | Low risk |
| Glewwe et al., 201611 | Cluster RCT Two counties of Gansu province, China; 2004 |
Treatment: Eye examinations with provision of free eyeglasses Control: Students were screened for vision problems, but did not receive eyeglassesc |
Students with poor vision in grades 4–6 in rural primary schools: Treatment: n = 1528 Control: n = 1001 (Regression results include 16 373 students with good vision in both treatment and control schools) |
After one school year, the intervention group had higher difference in academic achievement, 0.11 SD improvement in test scores relative to the control group | Some concerns |
| Naidoo et al., 201610 | Prospective cohort study, no control group KwaZulu-Natal, South Africa; No year reported |
Provision of free eye eyeglasses to address presbyopia | Textile workers aged ≥ 40 years performing near vision tasks in clothing factories (n = 268) | After 6 months, a 6.4% increase in production passing quality assurance per day | Serious risk |
| Ma et al., 201813 | Cluster RCT Yongshou county, Gansu province, China; 2014 |
Teacher screening followed by referral to vision centre to address myopia in students; The treatment group received early referral and the control group received late referral | Students at rural primary schools in grades 4–6 with uncorrected visual acuity of ≤ 6/12 (Snellen) in either eye Treatment: n = 433 Control: n = 516 |
4–6 months after referral to vision centre, the intervention group had higher academic achievement, 0.25 SD improvement in test scores relative to the control group | Some concerns |
| Reddy et al., 20189 | Individual RCT Assam, India; 2017 |
Treatment: Eye examination with provision of eyeglasses for presbyopia Control: Eye examination with deferred provision of eyeglasses for presbyopia |
Tea pickers aged ≥ 40 years with near visual acuity ≤ 6/12 at 40 cm (presbyopia in both eyes) Treatment: n = 376 Control: n = 375 |
During the 11-week harvest season, treatment group had a 5.25kg higher average daily weight of tea picked, a 21.7% relative increase, compared to control group | Low risk |
| Glick et al., 201951 | Prospective cohort study with control group Amhara region, Ethiopia; 2012 |
Exposed: Free cataract surgery Unexposed: No intervention |
Exposed: Individuals who were bilaterally blind from cataract, defined as presenting visual acuity in the better eye < 20/400 (n = 426) Unexposed: Blind individuals who were ineligible for cataract surgery (n = 471) |
12-month follow up: difference-in-difference: 3.1% higher per capita consumption | Moderate risk |
| Nie et al., 202055 | Cluster RCT Shaanxi province, China; 2014 |
Treatment: Eye examination and provision of free eyeglasses Control: Eye examination with prescription provided. Eyeglasses provided after end of study |
Grade 7–8 junior high school students Treatment: n = 476 Control: n = 434 |
After one school year, treatment group had 0.141 higher SD in test scores and 2.1 percentage point fewer drop outs compared to the control group | Some concerns |
| Ma et al., 202114 | Cluster RCT Gansu and Shaanxi province, China; 2013 |
Treatment: Eye examination and provision of free eyeglasses Control: Participants received a prescription for eyeglasses |
Grade 5 students attending public primary schools Treatment: n = 1702 Control: n = 1763 |
After one school year, the intervention group had higher academic achievement, 0.14 SD improvement in math test scores relative to the control group | Some concerns |
| Ma et al., 202114 | Cluster RCT Jiangsu province, China; 2014 |
Treatment: Eye examination and provision of free eyeglasses Control: Participants received a prescription for eyeglasses |
Grade 5 students attending migrant primary schools Treatment: n = 2163 Control: n = 2246 |
After one school year, 0.046 SD increase in math test scores in the treatment group relative to the control group | Some concerns |
| Du et al., 202247 | Cluster RCT; Rural county areas of Tianshui city, Gansu province, China; 2012 |
Treatment: Eye examinations with free eyeglasses delivered to schools four weeks later Control: Eye examinations with prescription for free eyeglasses |
Students at rural primary schools in grades 4–5 with uncorrected visual acuity ≤ 6/12 in either eye; Treatment: n = 383 Control: n = 379 |
After one school year, the intervention group had higher academic achievement, 0.123 SD improvement in test scores relative to the control group | Some concerns |
| Du et al., 202247 | Cluster RCT; Rural county areas of Yulin city, Shaanxi province, China; 2012 |
Treatment: Eye examinations with free eyeglasses delivered to schools four weeks later Control: Eye examinations with prescription for free eyeglasses |
Students at rural primary schools in grades 4–5 with uncorrected visual acuity ≤ 6/12 in either eye; Treatment: n = 716 Control: n = 609 |
After one school year, the intervention group had higher academic achievement, 0.032 SD improvement in test scores relative to control group | Some concerns |
| Latif et al., 202254 | Prospective cohort study, no control group Lahore, Pakistan; No year reported |
Eye examinations and provision of free corrective eyeglasses | High school students (grade 6–10) across five local unit of an administrative division n = 253) | Higher academic achievement average test scores increased from 56.39 to 60.27 in public schools (equivalent to 0.29 SD improvement) | Serious risk |
| Sagemüller et al., 202256 | Cross-sectional survey with propensity score matching rural workers in the Cambodian agricultural sector, Cambodia; 2017–2018 |
Exposed: Provision of eyeglasses for visual impairment (implied) Unexposed: No intervention |
Exposed: Workers with visual impairment (n = 179) Unexposed: Wokers without visual impairment (n = 76) |
Treatment effect on the treated: Individuals with poor vision have US$ 630 lower farm profit compared to matched sample with good vision | Moderate risk |
| Huang & Chen, 202352 | Cross-sectional fuzzy regression discontinuity China Education Panel Survey, China; 2014–2015 |
Provision of eyeglasses to those with visual impairment (implied) | Grade 8 students (n = 3987) | Treatment effect on the treated: Those who wore glasses had higher academic achievement, 0.24 SD improvement in math test scores, 0.27 SD improvement in Chinese test scores | Low risk |
RCT: randomized controlled trial; SD: standard deviation; US$: United States dollars.
a RCTs were assessed using the Cochrane risk of bias tool for RCTs, which has three categories: low risk of bias, some concerns, high risk of bias. Observational studies were assessed using the Cochrane risk of bias tool for observational studies which has four categories: low risk of bias, moderate risk of bias, serious risk of bias and critical risk of bias.
b Productive activities are household work, paid work, or work for own use.
c Several townships were not compliant and provided control students with eyeglasses. These townships were excluded from the statistical analysis in the study’s preferred results.