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Editors Selection IGR 10-3

Response

Comment by Nomdo Jansonius on:

21848 The additional yield of a periodic screening programme for open-angle glaucoma: A population-based comparison of incident glaucoma cases detected in regular ophthalmic care with cases detected during screening, Stoutenbeek R; de Voogd S; Wolfs RC et al., British Journal of Ophthalmology, 2008; 92: 1222-1226

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Our colleagues raised a number of interesting and relevant points with regard to our study on the additional yield of a periodic screening program for open-angle glaucoma. In this study, we used follow-up data from the population-based Rotterdam Study to simulate a periodic screening. Time between the studied screening and the previous screening was on average 6.5 years. We estimated that, in a white population with a low prevalence of pseudoexfoliation, about one in 1000 screened persons could be saved from bilateral end stage glaucoma by repeat screening.

The four main issues raised were (1) the fact that the health care system in the Netherlands might be better than average; (2) the less than optimal response rate; (3) the impact of loss of quality of life in earlier disease stages; and (4) the fact that findings at baseline (that is, the previous screening) might have increased awareness especially in persons with a larger CD-ratio or a positive family history of glaucoma.

Data regarding the apparently well-organized health-care system in the Netherlands were derived from an earlier study (Stoutenbeek et al. BJO 2006; 90: 1242). That study was a population-based survey addressing the most recent visit to an optician or ophthalmologist among 1200 inhabitants aged > 40 years of the Netherlands. Eighty- four (84) percent had visited either an optician or an ophthalmologist in the last five years; neither the place of living (city, town or village) nor educational level (a proxy of socio-economical status) was associated with this percentage (but variability in socio-economic status may be smaller in the Netherlands than somewhere else). Although 84% seems high, similar numbers are not available for most other countries and it would be interesting to repeat this study in other countries. Moreover, having visited an optician, or even an ophthalmologist, is not the same as being screened for glaucoma. Increasing glaucoma awareness amongst health care professionals might be more efficient than screening (many glaucoma cases found in population based studies had a history of a recent ophthalmologist visit without a diagnosis of glaucoma or even glaucoma suspect).

The response rate at follow-up was 78%. Non-participants had on average a higher age, more often a history of stroke or dementia and were more often institutionalized (de Voogd et al. Ophthalmology 2005; 112: 1487), suggesting a significantly shorter life-expectancy in non-participants. The average CD-ratio at baseline was similar in participants and non-participants. From the point of view of epidemio logy, any less than perfect response rate has to be regretted. When using these data for studying the yield of a screening program, however, this number is part of the result: it is the best available estimate of (non-)response to a call for a glaucoma screening.

Having visited an optician, or even an ophthalmologist, is not the same as being screened for glaucoma. Many glaucoma cases found in population-based studies have a history of a recent ophthalmologist visit without a diagnosis of glaucoma or even glaucoma suspect

We agree that an earlier stage than bilateral end stage disease may have a significant impact on quality of life. Our discussion on this topic was � due to the BJO word limit � reduced to a single line indicating thatone in 200 screened persons could be saved from unilateral end-stage disease by periodic screening. Even more important could be the prevention of bilateral small but overlapping paracentral scotoma, an issue that is not easily addressed reliably, even in this large study.

One in 200 screened persons could be saved from unilateral end-stage glaucoma by periodic screening

The baseline study (that is, the previous screening) might have influenced the yield of the follow-up examination. Especially participants with ocular hypertension had to be informed. Disc photographs were analyzed later and will therefore not have influenced the awareness of the participants: if the visual field was normal, patients with larger CD-ratios were not informed. Asking for a family history may have induced some awareness, but, within the Rotterdam Study, this question was just one of several hundreds of questions addressing all aspects of health, environment, and so on. But, obviously, some awareness cannot be ruled out and we agree that this might have been a source of confounding, especially when more fundamental epidemiological issues are studied. However, similar to the issue of non-participation, any awareness generated at baseline is, when using these data for studying the yield of a periodic screening program, part of the result. If the yield of a repeat screening is very small because of awareness generated at baseline, then a valid conclusion is that a good glaucoma screening program could be a once-in-a-lifetime screening at a certain age combined with education of the participant at that moment (that is, informing especially those with borderline IOPs or disc findings, a positive family history, and so on).
A good glaucoma screening program could be a once-in-a-lifetime screening at a certain age combined with education of the participant at that moment.

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