Table 3

Model inputs for cost effectiveness analysis of screening strategies for uncorrected refractive error in schoolchildren in WHO sub-Saharan African sub-region AfrE

Variable	Assumption	Data source
Target population
Primary school enrolment rate	63%	Unicef²⁵
Secondary school enrolment rate	27%	Unicef²⁵
Health effects
Health state valuation of visual impairment	0.755	Burden of disease study²⁶
Remission rate of uncorrected refractive error (without screening or treatment)	0	Assumption*
Remission rate of uncorrected refractive error (intervention scenarios)	1.09	Calculation†
Compliance with wearing provided glassess	70%	Assumption based on Limburg et al²⁷ in India; Hogeweg et al²⁸ in Nepal‡
Costs ($Int)
Training§:
No of children to screen per teacher (5–10 years old)	165	Limburg et al²⁹ in India¶
No of children to screen per teacher (8 years old)	50
No of children to screen per teacher (11–15 years old)	165
No of children to screen per teacher (13 years old)	100
Duration of training (days)	1	Assumption*
Repetition of training (every number of years)	5	Assumption*
Cost per teacher to train (cost per day)	45	WHO-CHOICE
Screening costs:
Ratio of true positive:false positive cases	1:3.6	Limburg et al²⁹ in India¶
Useful life of glasses (years)	4	Assumption*
Screening material costs (tape, card etc)	10	Assumption*
Treatment at health clinic:
Cost of ophthalmic assistant:
Time spent per patient (minutes)	15	Assumption*
Annual salary	7968	WHO-CHOICE
Costs of ophthalmic equipment:
Costs of set	4	WHO-CHOICE
Useful life (years)	10	Assumption*
Average annual patient load	6400	Assumption*
Costs of spectacles:
Purchase price	5	Assumption*
Useful life (years)	4	Assumption*
Costs of outpatient visits:
No of visits	4.6	Limburg et al²⁹ in India¶
Costs of visits at secondary hospital level	500	WHO-CHOICE
Discount rate	3%	WHO-CHOICE

*Based on personal communication with Dr Mariotti (WHO) and Dr Limburg (independent consultant), both specialists in ophthalmology in low and middle income settings.

†Formula is −LN(1−(effectiveness×coverage)), with effectiveness equal to compliance and coverage as defined in intervention. The table lists the remission rate for a coverage of 95%.

‡Estimates based on two studies in the respective regions, and are in line with findings from other studies in China³⁴ and Thailand.³⁵

§The number of teachers to train depends on the number of schoolchildren that one teacher can screen and, ultimately, on school size. In screening of children aged 5–10 years, a trained teacher can serve all classes in the school, on average 165 children. In case only children of aged 8 years are screened, the teacher can screen only that class, on average 50 children. The same logic applies to screening at secondary school.

¶To our knowledge, this is the only study that provides the required details on costs of screening for refractive error in a low income setting and has therefore been used as the basis for our estimates.