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Editors Selection IGR 12-2
Structure and function measurements: Visual field index and rate of progression
Comment by Chris Johnson on:
20340 A visual field index for calculation of glaucoma rate of progression, Bengtsson B; Heijl A, American Journal of Ophthalmology, 2008; 145: 343-353
In recent years, there has been considerable emphasis on the early detection of structural and functional glaucomatous damage. However, to most glaucoma specialists, a critical concern for monitoring the status of glaucoma patients is to be able to determine the rate or progression to estimate the impact of glaucoma on quality of life and make informative management and treatment decisions. Bengtsson and Heijl (442) have now introduced a visual field index for calculating the rate of progression of glaucomatous visual field loss. The study has been performed carefully and should be a valuable clinical tool. In particular, the authors have conducted an evaluation of the influence of cataract on the rate of progression index. Representative examples are presented in the paper. Ultimately, the value of this procedure will depend on whether or not it is clinically useful, which will be determined when other glaucoma specialists have an opportunity to employ this procedure. A key factor in this determi-nation, which is true for all research, is the validity of assumptions that are incorporated in this model of the rate of glaucomatous visual field progression.
Are the assumptions that are incorporated in this model of the rate of glaucomatous visual field progression valid?For example, the authors use the pattern deviation values as a means of minimizing diffuse loss from the influence of cataract. However, there are several investigators who have demonstrated that diffuse visual field loss can also be produced by glaucoma, and that total deviation values can sometimes be more informative than pattern deviation values. Additional considerations are whether the rate of visual field progression is linear (as the authors assume) or non-linear, and the period of follow-up time that is necessary to use this tool effectively. Other assumptions may also impact on the validity and usefulness of this procedure, and the response from other glaucoma specialists will help to define its final role. It is encouraging that this procedure will now be available for clinicians who follow glaucoma patients because there has been a lack of thorough, careful research on this topic in the past.
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