Eyeglasses to Improve Workers' Manual Dexterity
This is an interim intervention report. We have spent limited time to form an initial view of this program and, at this point, our views are preliminary. We plan to consider undertaking additional work on this program in the future.
- What is the program? Providing free or subsidized eyeglasses to workers whose productivity – and therefore income – depends on their manual dexterity.
- What is its evidence of effectiveness? There is evidence from one randomized controlled trial (RCT) that distributing eyeglasses markedly improves productivity among tea pickers with impaired near vision in India. Given the simple nature of the intervention, we believe that this evidence is likely to at least partly generalize to other workers who rely heavily on their manual dexterity.
- How cost-effective is it? Our best guess is that this intervention is within the range of cost-effectiveness of programs we would consider directing funding to.
- Does it have room for more funding? Our initial analysis suggests that there are a large number of people with vision problems who could potentially benefit from these programs, but we have not yet assessed what funding gaps exist for particular charities working in this area.
- Bottom line: This program appears promising, and we plan to continue our investigation when we have available capacity. We expect our next steps to include: 1) Better understanding what philanthropic opportunities exist to support this kind of program, 2) Assessing whether and how the evidence discussed in this report could be applied to populations other than teapickers.
Published: April 2019
Table of Contents
What is the problem?
The World Health Organization (WHO) reports that 1.3 billion people are estimated to live with some form of distance or near vision impairment.1 Of these, 826 million have near vision impairment, or presbyopia.2 The WHO considers about 80% of vision impairment to be avoidable.3
Those suffering from visual impairment may experience a loss of productivity at work, which may, in turn, affect their incomes and employment opportunities. These economic effects are likely to be especially pronounced for individuals who rely on their manual dexterity (fine motor control) and/or visual discrimination for their work.
What is the program?
Eyeglasses are distributed (either for free or at a subsidized rate) to people whose ability to be productive at work is constrained by their impaired near vision. Typically, we would expect beneficiaries to be screened to determine their needs.
This program is narrower in focus than general distribution of eyeglasses in developing countries, which we considered in this broader report on distribution of eyeglasses in developing countries.4
Does the program have strong evidence of effectiveness?
There is evidence from one randomized controlled trial (RCT), Reddy et al. 2018, that distributing eyeglasses markedly improves productivity among tea pickers with impaired near vision in India. Given the simple nature of the intervention, we believe that this evidence is likely to at least partly generalize to other workers who rely heavily on their manual dexterity.
Reddy et al. 2018 is an RCT conducted on tea pickers in Assam, India.5 It found that, among the population of workers diagnosed with presbyopia, those randomly selected to receive eyeglasses experienced a 21.7% increase in productivity (95% confidence interval: 18.6-24.8%), measured in terms of the weight of tea picked, relative to those who did not.6 These effects were exhibited in the short-term: output was measured over an 11-week period immediately following treatment.7
We assessed whether Reddy et al. 2018 had any basic methodological limitations and did not identify any major issues. However, we have not yet deeply scrutinized this study. Some of the key characteristics of the study that give us confidence in its results include:
- It is a pre-registered randomized trial.8
- The sample size was 751 participants.9
- There do not appear to be any statistically significant differences between the treatment and control groups at baseline.10
One possible limitation of the study is that participants could not easily be blinded due to the nature of the intervention.11 However, "placebo" effects seem unlikely; the outcome (daily weight of tea picked) was objectively measured by masked assessors using a scale.12
In addition, some of the more detailed results are intuitively plausible and support the mechanism in question. In particular, the productivity gains were greatest among older workers, whose vision is likely to have deteriorated more markedly (and the authors pre-registered their intention to test for interactions with age, decreasing the potential for a misleading subgroup finding).13
Aside from Reddy et al. 2018, it appears (based on a cursory search) that the evidence base for distributing eyeglasses leading to improvements in productivity is relatively thin. We did not find any other studies on this topic that were both highly relevant and convincing. For more information, see the following footnote.14
There is also some evidence that distributing eyeglasses improves test scores for school children (see footnote for details).15
How cost-effective is the program?
Based on a cost-effectiveness model we put together in October 2018, modified in April 2019, and updated with our most recent moral weights as of February 2021, we estimate that this program is within the range of cost-effectiveness of the opportunities that we expect to direct marginal donations to (about 10x cash or higher, as of 2021).16
Note that our cost-effectiveness analyses are simplified models that do not take into account a number of factors. There are limitations to this kind of cost-effectiveness analysis, and we believe that cost-effectiveness estimates such as these should not be taken literally due to the significant uncertainty around them. We provide these estimates (a) for comparative purposes and (b) because working on them helps us ensure that we are thinking through as many of the relevant issues as possible.
Major uncertainties in our preliminary cost-effectiveness model include:
- How would these results generalize to other settings? We adjust our estimates downward somewhat as we expect that the effects of the program will not be as large for workers in other settings as they were estimated to be for tea pickers.17
We do not have a strong sense of how effects on productivity might vary in related populations of workers who require a high level of manual dexterity and/or visual discrimination, such as other agricultural pickers and textile workers. It seems possible that the target population in Reddy et al. 2018 (tea pickers in Assam) was chosen because it was expected to be particularly responsive to eyeglass distribution, so we would expect cost-effectiveness to be at least somewhat lower in other settings.
- How long do the benefits of the eyeglasses last for? We made the simplifying assumption that the eyeglasses last two years. This is based on a number published by one charity working in the field, which we have not scrutinized.18 We also do not have a strong sense of how frequently recipients typically use their eyeglasses.19
- For how much of the year do workers benefit? Reddy et al. 2018 study productivity over an 11 week portion of the tea-plucking season. In our model, we assume that recipients experience similar increases in productivity across the entire five-month plucking season for tea leaves. It is possible that workers also experience income gains as a result of improved vision across the remainder of the year, either through tea-plucking or other work, but we are not aware of any evidence that speaks to this and have not yet investigated it in detail. We also assume that workers directly gain a higher quality of life as a result of no longer having impaired vision, and that these benefits last all year round.
- How do the productivity gains translate into income? We have assumed that increases in productivity translate one-for-one into increases in labor income. In practice, although workers report that they would receive greater financial compensation by increasing output, it is likely that they do not reap the full benefits of their extra productivity. Nevertheless, it is very likely that someone does, such as the owner of the tea plantation, though the humanitarian benefits of this effect may be smaller.20
Does the program appear to have room for more funding?
Our initial analysis suggests that there are a large number of people who have vision problems and could potentially benefit from these programs, but we have not yet assessed what funding gaps exist for particular charities working in this area.
- Presbyopia affects about 826 million adults globally.21
- Our best guess is that eyeglasses are currently being distributed to workers in developing countries at a relatively low rate. One estimate, based on a limited survey, suggests that NGOs and some other organizations distributed 7.8 million eyeglasses in Latin America, Africa, and Asia in 2015.22
- We do not have a clear view on how much of the unmet need for eyeglasses is accounted for by workers in settings where visual impairment may be constraining their manual dexterity and therefore their productivity and income.
- However, we expect that the number of workers who could benefit is substantial: for example, according to one estimate from 2012, the tea industry in India alone employs around 3.5 million workers.23
Organizations that implement this program
We have not undertaken a comprehensive investigation into organizations that run programs to distribute eyeglasses to workers. Some relevant organizations that we are aware of include:
- VisionSpring is a social enterprise that provides eyeglasses in developing countries. It has some programs that involve partnering with businesses to distribute eyeglasses in the workplace – in particular, in the garment and textile industries.24
- Vision for a Nation, Sightsavers, Lions International, and Eyes on Africa all distribute eyeglasses in developing countries, but it was not obvious from a brief inspection of their websites that any of them target their programs at workers who rely on manual dexterity and/or visual discrimination. We have spoken to Vision for a Nation but have not yet followed up with Sightsavers, Lions International, Eyes on Africa, or any other charities for more information.25
Focus of further investigation
Topics we would focus on as part of further investigation include:
- Room for more funding: Our most important next step is to better understand what philanthropic opportunities exist to support eyeglasses programs targeted at workers. We would also want to consider whether distributing eyeglasses is a cause that is well-suited to philanthropy, or whether it is more appropriate for individuals or businesses to fund eyeglasses themselves. Frictions that may prevent individuals or businesses from purchasing eyeglasses – even if they confer productivity benefits – include stigma, liquidity constraints, lack of awareness, and logistical barriers.26
- External validity: A major priority is to assess whether and how the evidence discussed in this report applies to populations other than teapickers.
- Cost-effectiveness: Our cost-effectiveness analysis is preliminary and highly uncertain. If we investigate these programs further, we would probe the major uncertainties outlined above in more depth.
We previously conducted an interim intervention report on broader programs to distribute eyeglasses in developing countries. We initially concluded that there was not strong evidence demonstrating that distributing eyeglasses increases productivity. More recently, we learned about the study by Reddy et al. 2018, which directly speaks to this issue. We lightly scrutinized this study and used it as the basis for a cost-effectiveness analysis of this program. We also conducted a brief, non-exhaustive web search for other studies, reports, and charities that work in this area.
- 1 "Globally, it is estimated that approximately 1.3 billion people live with some form of distance or near vision impairment." WHO Vision Impairment Fact Sheet, 2018.
- 2"With regards to near vision, 826 million people live with a near vision impairment." WHO Vision Impairment Fact Sheet, 2018.
- 3"Approximately 80% of vision impairment globally is considered avoidable." WHO Vision Impairment Fact Sheet, 2018.
- 4 In particular:
- It targets workers in settings where impaired vision is likely to reduce manual dexterity, and, in turn, productivity and income, as opposed to programs that distribute eyeglasses to the population at large, which may focus more heavily on children.
- The form of vision impairment that these workers are likely to suffer from is presbyopia (age-related decline in near vision), as opposed to impaired distance vision.
“The poor vision of 2.5 billion individuals worldwide could be corrected by providing each with a pair of eyeglasses. Of this population, 624 million need corrective lenses so strong that they are classified as visually impaired or blind without glasses. The majority of these people are affected by nearvision loss due to presbyopia, meaning they are unable to see nearby objects clearly and need to use reading glasses. Presbyopia usually develops when adults are in the prime of their careers, affecting a vast range of activities and professions, from agriculture and food production, such as coffee- and cocoa-bean sorting, to garment and textile work. If left untreated, presbyopia causes gradual vision loss that can reduce productivity and lead to premature retirement.” World Economic Forum and EYElliance, "Eyeglasses for Global Development: Bridging the Visual Divide," 2016, Pg 24.
- 5"Participants in each stratum were randomly assigned (1:1) with a block size of six to the intervention or control groups... The randomization sequence was generated by the study statistician at the Clinical Trials Unit of the Zhongshan Opthalmic Center (Guangzhou, China) by use of an online random number generator (Randomization.com)." Reddy et al. 2018, Pg e1021.
- 6"The between-group difference (5.25 kg per day [95% CI 4·50–5·99]; p<0·0001) was equivalent to a 21·7% relative productivity increase." Reddy et al. 2018, Pg e1023.
- 7"The primary outcome (investigator-masked) was the difference between groups in the change in mean daily weight of tea picked (productivity), between the 4-week baseline period (June, 2017) and the 11-week evaluation period (July 24, 2017, to Oct 7, 2017)." Reddy et al. 2018, Pg e1019.
- 8"This trial is registered with ClinicalTrials.gov, number NCT02338199." Reddy et al. 2018, Pg e1019. See ClinicalTrials.gov, PROSPER study pre-registration, 2017.
- 9"Based on the examination, 751 (57·9%) workers were eligible for the trial and underwent stratification and randomisation, with 376 (50·1%) participants allocated to the intervention group and 375 (49·9%) to the control group." Reddy et al. 2018, Pg e1022.
- 11It would have been impractical for participants not to know they were wearing glasses. The study's authors note that "... for practical and ethical reasons, participants were not masked to study group assignment..." Reddy et al. 2018, Pg e1026.
- 12"Daily weight of tea picked by participants in both groups was assessed by masked APPL employees as follows during an 11-week evaluation period from 6 September 2018 July 24, 2017, to Oct 7, 2017. Intervention-group participants removed their glasses before proceeding to the weighing station. One employee received the sack of tea and suspended it on an electrical scale (Easyweigh, Applied Data Logix, Chennai, India), while a second, also masked to workers’ group assignments, swiped the participant’s work identification card. The scale automatically measured and recorded the weight in the APPL database." Reddy et al. 2018, Pg e1021-22.
- "Thus, the between-group difference in the change in productivity rose with increasing age (figure 2): 40–44 years (3·89 kg per day [95% CI 2·82–4·96], 15·8% of baseline); 45–49 years (4·79 kg per day [3·47–6·12], 18·9% of baseline), and 50 years or older (7·29 kg per day [5·90–8·68], 31·6% of baseline; p=0·0003, two-way ANOVA)." Reddy et al. 2018, Pg e1023.
- This test was noted in the documentation submitted as part of the trial's pre-registration:"Interaction of age and group will be examined, as it is expected that Interaction group participants will have a greater productivity response, while those in the Control may have less." PROSPER study pre-registration, full protocol, Pg 7.
- One other RCT, Glewwe and Schaffner, 2014, looks at the impact of eyeglass distribution among women who produce handwoven goods in Rwanda. They find that recipients of eyeglasses reported that they believed eyeglasses improved their weaving productivity, and that they were willing to pay a substantial amount for the eyeglasses: "...of the 47 women who received glasses immediately after the baseline sessions, 46 reported that the glasses allowed them to weave more quickly and more accurately, and the great majority of them (41 out of 47) reported their willingness to pay at least 2,000 Rwandan francs (Rwf) to replace their glasses. This is more than the 1,300 Rwf cost..." Glewwe and Schaffner, 2014, Pg 1. But the authors note that their research encountered some difficulties which meant that they were not able to draw any quantitative conclusions from the study. Given the lack of quantitative results, the small sample, and the lack of peer review, we do not place much weight on this study.
- Daum et al. 2004, a RCT conducted in a laboratory setting in the US, examines the impact of eyeglasses on the productivity of computer-oriented tasks. They find that providing spectacles leads to a 2.5-28.7% increase in productivity on a series of computer tasks (Daum et al. 2004, Pg 33). While this study does provide some corroborative evidence, the setting is so different from the programs under consideration that it is hard to infer much from it.
- Glewwe, Park and Zhou, 2016 and Ma et al. 2014, two RCTs conducted in China, find some evidence that distributing eyeglasses to children has a positive effect on test scores. Higher test scores might eventually lead to improved incomes and life outcomes, but the mechanism would be different from the direct effects on productivity for manual workers that we are considering in this report.For more information on distributing free corrective eyeglasses to children, see our previous interim intervention report.
- 15See our broader report on the impacts of eyeglasses, which provides more detail on effects on test scores, here.
- 16See our cost-effectiveness analysis of eyeglasses to improve workers' manual dexterity , “CEA” sheet, “Total cost-effectiveness relative to GiveDirectly” row.
- 17See this cell.
- 18See this assumption in the figure “Economic Impact of Reading Glasses,” under “Glasses and Socio-Economic Development” on VisionSpring website, "Landmark Study Proves and Quantifies Impact on Worker's Productivity"
- 19There is limited and mixed evidence on this point. One study (Laviers et al. 2010) finds that 82% still had their glasses after six months: "Among the 215 presbyopes re-examined at follow-up, 176 still had a presbyopic correction..." Laviers et al. 2010, Pg 1237. There is also a shred of evidence that adherence rates may be low. A report published by Sightsavers into their vision programs for truck drivers in India describes a set of phone surveys with a small proportion of recipients that found that "Only 17.9% of drivers... said they always used the spectacles they received from Sightsavers." Sightsavers, "Eyes OK Please!" Report, 2017, Pg 8.
- 20"...all agreed that “It is important to maximise my income by picking as much tea as possible.” Reddy et al. 2018, Pg e1022.
- 21"With regards to near vision, 826 million people live with a near vision impairment." WHO Vision Impairment Fact Sheet, 2018.
- 22Figure 3, World Economic Forum and EYElliance, "Eyeglasses for Global Development: Bridging the Visual Divide," 2016, Pg 12.
- 23"The tea industry is also India's second-largest employer with over 3.5 million workers employed in over 1,500 tea-growing estates." India Brand Equity Foundation, "Tea Industry in India," 2012
- 24For more detail on these programs, see GiveWell's non-verbatim summary of a conversation with Dr. Nathan Congdon, VisionSpring, and Clearly, November 12, 2018.
- 25For more detail on these programs, see GiveWell's non-verbatim summary of a conversation with Clearly and Vision for a Nation, November 1, 2018.
- 26For example, from New York Times, "A Simple Way to Improve a Billion Lives: Eyeglasses," 2018: “In rural India, glasses are seen as a sign of infirmity, and in many places, a hindrance for young women seeking to get married.”