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Editors Selection IGR 11-4
Prevention and Screening: Does screening affect glaucoma incidence and disease outcomes?
Comment by Christopher Girkin on:
49208 Projected clinical outcomes of glaucoma screening in African American individuals, Ladapo JA; Kymes SM et al., Archives of Ophthalmology, 2012; 130: 365-372
Lapado and colleagues recently published a study projecting the outcome of glaucoma screening in individuals of African ancestry using a Monte Carlo microsimulation model to project visual field impairment and blindness. Their model found that a nationwide screening program would reduce the incidence of glaucoma from 50% to 27% and the prevalence of blindness from glaucoma from 4.6% to 4.4%. The authors clearly acknowledge the many assumptions in this model and perform a sensitivity analysis on the number needed to screen based on a number of relevant parameters. It would be interesting to see the combined effects on some of these factors in the sensitivity analysis presented in the study. Factors like low followup rates and low treatment efficacy are very likely to been seen in harder to access populations and in combination would significantly alter the effectiveness of any screening program more than these single changes alone. Finally, while beyond the scope of the questions addressed in this excellent study, from a practical standpoint, all of the individuals screened in these high risk populations fall into categories in which the American Academy of Ophthalmology guidelines clearly state a yearly eye exam is recommended. Given this fact, why perform a screening test at all? The outcome is essentially the same in that the subject should be referred for a complete general eye examination whether they have a positive or a negative test. Further, it is unknown if screening has an untoward effect on patient adherence to later eye examinations as screened subjects may assume they have received a full examination and have normal ocular health. This may cause individuals with other diseases and with false negative tests to remain undiagnosed. A major problem in designing a care delivery model for any chronic occult disease is a low adherence to recommended eye examinations. It would be interesting to model how a focused screening program would perform against community-based eye health education programs. Prior studies by Cynthia Owsley and coworkers have shown disappointingly that a rigorously designed health education program does not significantly alter adherence with eye examinations. While the current study on screening does not assess this, the question remains if the screening process itself significantly alters usual care of a population for a prolonged period of time. This is especially important when considering care delivery to underserved populations with limited access and multiple barriers to receiving eye care.
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