The measurement of bulbar hyperemia: challenges and pitfalls

To review methods of assessing bulbar redness, particularly with respect to the practicality of comparing different rating systems.

The published literature was reviewed and discussed by a panel of experts and a narrative review prepared.

Bulbar hyperemia is a common clinical sign and an important indicator of ocular disease. As bulbar hyperemia is a frequent side effect of topical glaucoma medications, accurate objective measurement is important to allow comparison of clinical studies. A number of different measurement systems have evolved to allow quantification of subjectively assessed redness to be rendered into a form that allows between-treatment comparisons and longitudinal changes in both clinical research and practice. Whereas widespread use of image-based rating scales has improved the assessment of bulbar redness in clinical practice and clinical research, these techniques are less than ideal. The scales are subject to an intrinsic subjectivity and are suboptimal in differentiating the physiologic phenomenon of bulbar hyperemia. There is also a degree of interobserver and intraobserver variation; in some studies, average variation in scores exceed half the extent of the whole scale. Moreover, a lack of interscale validation has led to confusion in comparing the results from clinical studies that use different scales. In a recent series of studies, cross-calibration between the various scales in use has been attempted.

Whereas naive comparisons between the results obtained in studies using different bulbar redness scales can lead to erroneous conclusions, the tools exist to permit meaningful comparisons between rating systems and scales.