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Editors Selection IGR 9-4

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Comment by Felipe Medeiros 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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The results of Stoutenbeek et al. are based on a well-designed population- based study, with standardized criteria for open-angle glaucoma (OAG) definition and carefully selected methods to assess incident OAG (iOAG). However, there are also issues deserving careful interpretation. While we know that possible OAG cases at baseline were included in the incidence study, their distribution among detected and undetected iOAG cases is not reported. Uneven distribution among the groups could mean that there was a bias with regards to awareness for glaucoma, depending on the information provided to participants at baseline. Uneven distribution seems probable, based on the higher vertical cup-to-disc ratio at baseline in detected compared to undetected iOAG. Awareness seems to be an important confounder to consider and this is in line with the finding that family history of glaucoma at baseline, a parameter associated with increased awareness, was significantly more frequent in the detected compared with the undetected cases.

As the goal of glaucoma treatment is not only to prevent severe visual impairment or blindness, but to maintain the patient�s visual function and related quality of life, the prevention of earlier stage of damage than end-stage glaucoma may be of great importance

Undetected iOAG more often had glaucomatous optic neuropathy only as compared with detected cases. Based on this finding the authors conclude that the detected iOAG cases had a faster progressing disease. Higher rates of possible OAG at baseline among detected iOAG cases could explain, at least partially, difference in stage between detected and undetected cases. Further, this difference was not found when more strict criteria for OAG definition were applied and the proportion of definite OAG cases was the same in both the detected and undetected group.

Based on the findings presented in this report, it is fair that the authors conclude that the yield of a periodic screening program in terms of preventing severe visual impairment or blindness is lower than expected from the prevalence of undetected OAG. However, the percentage of 0.1% representing the yield of the periodic screening was calculated based on the four (7% of 55) undetected cases that would presumably become blind without treatment in the population studied. One would expect that this number of cases would have been higher in populations with higher prevalence of glaucoma. Also as the authors mentioned the high percentage of the Netherlands population having regular visits to eye care professionals may have contributed to the poor additional yield of the periodic screening as found in this study.

In addition, we need to keep in mind that these findings pertain to periodic screening and therefore should not be generalized to screening for glaucoma overall. What we should also emphasize is that 71% of iOAG cases had remained undetected. Further to that, one should consider that the goal of glaucoma treatment is not only to prevent severe visual impairment or blindness, but to maintain the patient�s visual function and related quality of life, meaning that the prevention of earlier stage of damage than end-stage glaucoma may be of great importance.

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