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Glaucoma Dialogue IGR 10-1

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Comment by Paul Healey on:

20389 Cost-effectiveness of treating ocular hypertension, Stewart WC; Stewart JA; Nassar QJ et al., Ophthalmology, 2008; 115: 94-98

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The major flaw of the study of Stewart et al. is the use visual acuity for utility values for glaucoma patients. For early glaucoma a utility value 0.68 was used and those with a 'moderate' visual field loss would have a utility value of 0.57. The authors have ignored the work by, e.g., Kobelt (Acta Ophthalmol Scand 2006; 84: 363-371), describing utility values in patients with glaucoma and ignored the impact of age on utilility values. Most of all, we should be worried that this major flaw was not stopped by the peer review process of the journal.

The authors used the OHTS as representative of ocular hypertensive subjects and data from randomized controlled trial for economic evaluation. In general, however, the data from randomized control-led trials are too 'small and tight' due to small sample sizes for economic evaluation, tight inclusion and exclusion criteria (selected patients), protocol driven costs (frequent tests and visits), short follow-up (the time horizon of the Markov model was only five years) considering all costs and outcomes and losses of follow-up. The patients of OHTS study may be regarded as a high-risk subjects, e.g., 35-44% (depending on the published report) of its patients had positive family history of glaucoma compared to 20% of the EMGT study in which subjects were found through screening. The numbers for myopia were 34% in OHTS and 17% in the EMGT study. The OHTS subjects represented 49% of those considered originally for enrollment. In the EMGT study, the enrolled patients represented 37% of glaucoma patients found through screening.

The fundamental question is, of course, whether we want to prevent glaucoma or glaucoma induced visual disability

In addition, there are several disruptive imprecisions and inconsis-tencies in the article regarding the referred literature which diminish the credibility of the scientific approach, e.g., the follow-up in the the EMGT study was six years leading to a 16% progression rate instead of 18% used by the authors. In addition, the medication use for OHT and non-progressed glaucoma in the model were the same (1.4). One would assume that with progression from OHT to glaucoma the medication would be increased. Re protocol driven costs, it is unlikely that visual fields will be tested twice a year in real life in every-day clinics.

It is not clear why the sensitivity analysis were performed for cost data only,e.g., not for sensitivity and specificity of diagnostic tests. The impact of false positives were not considered in the model. Finally, the fundamental question is, of course, whether we want to prevent glaucoma or glaucoma induced visual disability.

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