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ELECTRONIC ARTICLE |
* Department of Health Economics, University of Ulm, Ulm, Germany
Department of Ophthalmology II, University Eye Hospital Tübingen, Tübingen, Germany.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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0.5 (20/40) and 
1 line difference between eyes; B) same as A, but pass threshold 0.6 (20/32); C) same as A, plus cover tests and examination of eye motility and head posture; D) same as C, but pass threshold 0.6 (20/32); and E) refractive screening without cycloplegia using the Nikon Retinomax autorefractor. Methods. A decision-analytic model was used with a time horizon until diagnostic examination. According to the model, all 3-year-old children were screened in kindergarten with 1 of the screening methods. Children with positive screening results were referred to an ophthalmologist for diagnostic examination. Children with inconclusive screening results were either referred to an ophthalmologist directly (option 1) or rescreened by the same method after 1 year and referred to an ophthalmologist if rescreening was positive or inconclusive (option 2). Screening test characteristics and costs were estimated on the basis of a field study in which 1180 3-year-old children were examined by orthoptists in 121 German kindergartens.
Results. Compared with methods A option 1 (A-1), B-1, C-1, C-2, E-1, and E-2, there was at least 1 other method that was both less costly and more effective. The average costs per detected case were lowest for method A-2 (878 Euro), followed by methods B-2 (886 Euro), D-2 (908 Euro), and D-1 (965 Euro). When these methods were compared with each other, the additional costs per extra case detected were 1058 Euro (B-2 vs A-2), 1359 Euro (D-2 vs B-2), and 13 448 Euro (D-1 vs D-2).
Conclusions. Monocular visual acuity screening with rescreening of inconclusive results had a favorable cost-effectiveness. By adding additional test items, few more cases could be detected. Because of a great proportion of false-negative, false-positive, and inconclusive results, refractive screening was less effective with an unfavorable cost-effectiveness.
Key Words: screening • amblyopia • kindergarten • cost-effectiveness
Abbreviations: ICER, incremental cost-effectiveness ratio • CER, cost-effectiveness ratio
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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In Germany, vision assessment is part of general preventive care examinations performed by general practitioners and pediatricians on children at 21 to 24 months and 42 to 48 months of age. These voluntary examinations are paid for by the social health insurance, which covers approximately 90% of the German population, as well as by private health insurance, which covers almost 10%. Although 71% to 95% of all eligible children participate in these examinations,10 the effectiveness of vision assessment in detecting amblyopia is considered poor11,12 because general practitioners and pediatricians lack experience with ophthalmologic tests necessary in these age groups.13
Screening by orthoptists has been proposed as one option to improve vision screening.14,15 Orthoptists are specialized medical aides with a thorough training in infant and child vision assessment, ocular motility disorders examinations, and amblyopia management. In most children, monocular visual acuity can be assessed reliably by simple screening methods from age 3 onward.16 Therefore and because clinical experience holds that treatment is most effective when administered as early as possible, the fourth year of life is considered best for vision screening programs.17,18 From this age, children in Germany are entitled by law to be admitted to kindergarten on parents’ request. As >50% of children enter kindergarten at age 3 and >80% attend kindergarten at age 4,19 screening programs conducted in kindergarten provide easy access to children without inconveniencing parents.20,21
The purpose of this study was to compare the effectiveness and cost-effectiveness of different methods of screening for amblyopia conducted by orthoptists in kindergarten. The screening methods analyzed were visual acuity testing with and without cover tests and examination of eye motility and head posture, as well as refractive screening using the Nikon Retinomax autorefractor (Nikon GmbH, Düsseldorf, Germany). The Retinomax is a portable, hand-held, monocular autorefractor that uses a fogging technique (which eases relaxation of accommodation) to measure the objective refraction.22
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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jcbarry/goe.html). According to the model, all 3-year-old children were screened for untreated amblyopia in kindergarten by 1 of the screening methods to be compared. Children with positive screening results were referred to an ophthalmologist for diagnosis. With respect to children with inconclusive screening results, 2 model options were distinguished: in option 1, children with inconclusive screening results were referred to an ophthalmologist directly (Fig 1); in option 2, children with inconclusive results were rescreened by the same method after 1 year and referred to an ophthalmologist if rescreening was positive or inconclusive (Fig 2).
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Screening Methods
Five different screening methods were compared (visual acuity thresholds are reported in usual 20/X notation; however, the test distance used in the study was 10 ft, not 20 ft):
0.8 (20/25) monocular visual acuity in both eyes, or 0.5 (20/40) in both eyes and 1 line difference between the visual acuity of the right and left eye (L. Hyvärinen, Lea-Test Ltd, Helsinki, Finland, personal communication, 1998). 0.8 (20/25) monocular visual acuity in both eyes, or 0.6 (20/32) in both eyes and 1 line difference between the visual acuity of the right and left eye. -1D and 3D, cylindric power 1.5D, and spherical equivalent anisometropia 1D. Screening results were classified as positive (when any screening item was abnormal), negative (when all screening items were within normal limits), or inconclusive (when cooperation was insufficient).
For each screening method, the 2 model options were analyzed, resulting in 10 method-option combinations labeled A-1 (for visual acuity screening A in model option 1) through E-2 (for refractive screening E in model option 2).
Model Parameters
The parameter values used in the decision-analytic model are shown in Table 1.
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0.4 (20/50) in either eye, or if the difference of visual acuity between the right and the left eye was 3 lines.
Costs of Screening Examinations
The costs of screening examinations were estimated on the basis of results of the field study in which the costs of orthoptic screening and device-based screening were calculated on the basis of comprehensive and detailed measurement of working time, material costs, and travel costs.25 Working time was divided into office time for organizing the screening program (organization time) and time for visiting the kindergartens. The latter was subdivided into travel time, time for preparing the examination site in the kindergarten, and examination time. Material costs included costs for orthoptic materials, stationery, parent information leaflets, postage, and telephone. Estimates of the costs of the screening methods analyzed in this study were derived as follows: costs of methods C and D were assumed to be equal to the costs of the orthoptic examination calculated in the field study. For visual acuity testing (methods A and B), it was assumed that examination time would be 25% less than for the orthoptic examination, all other working times being equal. For the autorefractor (method D), it was assumed that examination time was equal to what was measured for device-based screening, all other working times being equal to the other screening methods analyzed. Furthermore, investment costs and maintenance costs of the Nikon Retinomax autorefractor were included in the cost calculation. For calculating labor costs, working time was valued at 23.31 Euro/h (0.39 Euro/min). This amount corresponds to the tariff class Vb of the German Federal Employee Tariff (Bundesangestelltentarif), which applies to salaried orthoptists working in the public health sector in the year 2000 and includes all ancillary wage costs.
Costs of Ophthalmologic Examinations
Costs of ophthalmologic examinations were calculated to be 36.40 Euro, based on the German social health insurance’s relative value scale for outpatient physician services (Einheitlicher Bewertungsmaßstab für Ärzte26), which states point volumes for each service. A conversion factor (point value) of 0.041 Euro was used. For those covered by the social health insurance, there is no copayment for physician services.
Effectiveness and Cost-Effectiveness Ratios
Effectiveness was defined as the proportion of detected cases of untreated amblyopia in all cases of untreated amblyopia among the participating children. Average cost-effectiveness ratios were calculated for each screening method by dividing the total costs (for screening tests and ophthalmologic examinations) of the respective screening program by the number of newly detected cases of untreated amblyopia. Incremental cost-effectiveness ratios (ICER) were calculated by dividing the additional costs of a screening method compared with another screening method by the additional units of effects of this screening method compared with the other screening method: ICER = (costsmethod X - costsmethod Y)/(effectsmethod X - effectsmethod Y).
Sensitivity Analysis
Sensitivity analysis was performed to test the influence of uncertainty in screening method-specific model parameters on the cost-effectiveness. For this purpose, screening method-specific parameter values for sensitivity and specificity were varied according to their 95% confidence intervals found in the field study. For the parameter "costs per single screening test," the baseline value was decreased and increased by 25% each.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Figure 3 illustrates for a screening population of 1180 children that for 6 of the analyzed method-option combinations (A-1, B-1, C-1, C-2, E-1, E-2), there was at least 1 other option associated with both lower costs and greater effects. Thus, these 6 method-option combinations were so-called "dominated" and could be excluded from additional analysis. Among the remaining method-option combinations, visual acuity testing in option 2 (A-2) had the best average cost-effectiveness ratio of 876 Euro per detected case. By increasing the pass threshold for monocular visual acuity to 0.6 (20/32) in method B-2, additional costs of 1176 Euro would arise and 1.11 calculated additional cases would be detected. The ICER of B-2 versus A-2 would be 1058 Euro per additional case detected (1176 Euro/1.11), which is reflected by the slope of the line between A-2 and B-2 in Fig 3. Analogously, the ICER of D-2 versus B-2 and of D-1 versus D-2 would be 1359 Euro and 13 448 Euro, respectively.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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0.6 (20/32) instead of 0.5 (20/40) and by adding the cover tests and examination of eye motility and head posture. Both changes caused more children to screen positive, among whom were both true positives (which increased sensitivity) and false positives (which decreased specificity). The increase in effectiveness resulting from these changes was approximately 4% each. Refractive screening led to many false-positive and inconclusive results, thus inducing additional ophthalmologic examinations that resulted in an unfavorable cost-effectiveness. Furthermore, the comparatively low sensitivity of refractive screening brought about the lowest effectiveness of the screening methods compared.
For all screening methods, it was more cost-effective to rescreen children with inconclusive results than to refer them to an ophthalmologist directly. It may be sufficient to perform rescreening after 1 year because treatment started in the fifth year of life still is considered to be effective.27
Incremental analysis showed that only 4 method-option combinations were not dominated by other combinations, which means that compared with these 4 combinations, no other combinations were both less costly and more effective and thus clearly preferable. When these 4 combinations were compared, ICERs ranged from 1058 Euro to more than 13 000 Euro per additional case detected. On the basis of this information, a decision maker may choose the most suitable method-option combination taking into account the maximum limit he or she is willing to spend to detect an additional case.
Sensitivity analysis of screening method-specific parameters showed reasonably stable results. Only uncertainty with respect to the sensitivity of refractive screening had substantial influence on the CER, yet even when the most favorable parameter value was used, refractive screening was less cost-effective than all other methods analyzed.
It is important to point out that the average CER is almost inversely proportional to the prevalence rate of untreated amblyopia in the screening population. If, for example, in a different population the prevalence were twice as high as assumed in the model, then the average CERs for all screening methods would approximately be cut by half. Interested readers may test the influence of the prevalence rate as well as other model parameters on the CER by using a Microsoft Excel spreadsheet provided as freeware by the authors (download available as freeware for scientists at www.medizin.uni-tuebingen.de/jcbarry/goe.html).
The data on screening test characteristics used in the decision-analytic model were obtained from a field study in which screening was performed by orthoptists. The most important screening test item was visual acuity testing. The high sensitivity and specificity of visual acuity testing was most likely attributable to the orthoptists’ training and experience in vision assessment of children. In many European countries, such as Germany and Great Britain, orthoptists are trained in sufficient numbers, and thus an orthoptic screening program could probably be implemented easily. In other countries, such as the United States, orthoptists may not be available, which raises the question of whether screening personnel without orthoptic training could achieve similar results. In Sweden, visual acuity screening has been performed successfully by nurses specialized in screening children,27 and similar screening test characteristics have been reported.2,28 The authors know from experience that nurses and other medical aides can perform visual acuity testing according to ophthalmologic standards in preschool children provided that they have received adequate training and perform visual acuity testing routinely and frequently. Thus, it can be expected that visual acuity testing performed by trained personnel other than orthoptists may be similarly effective and cost-effective.
Other visual acuity tests with standardized optotypes suitable for children5 are likely to yield similar results if used strictly according to their manuals. The authors chose the Lea single optotype test because it combines high testability, high sensitivity for amblyopia, and reduced test time compared with line tests.29 However, if other tests are used, then the thresholds may have to be adjusted to achieve similar test characteristics.
In this study, costs were calculated from a third-party-payer perspective on the basis of resource prices from the German health care system. Because there was no copayment by the parents, neither for the screening nor for the diagnostic ophthalmologic examinations, calculated costs include all medical costs. Obviously, resource prices may be different in other countries, such as the United States. The use of gross domestic product purchasing power parities for currency conversion adjusts for differences in the general price level of different economies. In 2000, the purchasing power of 1 Euro in Germany was almost equal to the purchasing power of 1 US dollar in the United States. However, gross domestic product purchasing power parities do not account for differences in relative prices of health care compared with the prices of all goods and services. According to the most recent data available for 1996,23 relative prices of health care in the United States were approximately one third higher than in Germany, which could cause cost figures for the United States to be higher in this order of magnitude.
The CER of visual acuity screening in kindergarten with and without cover tests and examination of eye motility and head posture found in the study falls within a range likely to be acceptable for decision makers. Because visual acuity testing is a simple and accurate screening method, comparable results can be expected in other health care systems provided that access to children is easy and that the prevalence of untreated amblyopia is not fundamentally different.
Like many published cost-effectiveness analyses of screening programs and diagnostic tests in other areas of medicine, this study considered only costs and effects that occurred up the clinical endpoint "diagnosis." It provides information on how efficient different methods are in achieving the target of early detection of amblyopia. However, diagnosis of amblyopia is only an intermediate target. A more comprehensive evaluation of vision screening would also take into account the cost-effectiveness of subsequent treatment. Such an analysis would have to compare the costs and long-term effects, including the impact on quality of life, associated with treated and untreated amblyopia. At this time, such a comprehensive evaluation is not possible because sufficient data on the effectiveness of treatment and on the disability caused by amblyopia are not available.30
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Reprint requests to (H.-H.K.) University of Ulm, Department of Health Economics, Helmholtzstr 22, D-89081 Ulm, Germany. E-mail: hans-helmut.koenig{at}mathematik.uni-ulm.de
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REFERENCES |
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This article has been cited by other articles:
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  C Williams, K Northstone, R A Harrad, J M Sparrow, and I Harvey Amblyopia treatment outcomes after preschool screening v school entry screening: observational data from a prospective cohort study Br. J. Ophthalmol., August 1, 2003; 87(8): 988 - 993. [Abstract] [Full Text] [PDF]
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