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Editors Selection IGR 16-4

Clinical Examination Methods: Reliability of Visual Fields

Comment by Chris Johnson on:

73414 Evidence-based Criteria for Assessment of Visual Field Reliability, Yohannan J; Wang J; Brown J et al., Ophthalmology, 2017; 124: 1612-1620

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Perimetry and visual field testing are diagnostic test procedures that are typically employed to evaluate the status of peripheral visual function in patients with glaucoma or who are at risk of developing glaucoma. Because this is a test that requires subjective responses to stimuli presented at key locations in the peripheral visual field, the reliability of the test results is an important factor for the practitioner to assess in order to determine how much importance to assign to the perimetric findings.

Fixation losses did not influence MD values to any appreciable extent, but false positives elevated MD, and increasing amounts of false negatives and test time decreased MD values

The impact of reliability criteria on sensitivity measures and summary statistics is crucial for proper interpretation of these test results. Methods of monitoring the accuracy of steady fixation through gaze tracking (monitoring the location of the corneal reflex in relation to the edges of the pupil) and fixation losses (responses to a stimulus presented to the blind spot) provide a means of determining the level of cooperation demonstrated by the patient during a visual field examination. Additionally, catch trials in the form of false positives (responses when no stimulus is presented, or responses that fall outside of a predetermined time window in relation to the stimulus presentation) and false negatives (lack of responses to a stimulus presented at a higher intensity than a previously determined threshold at locations with normal or near-normal sensitivity) provide information about the consistency of the response properties of the patient. As indicated by the authors, the normal "cutoffs" for these values were determined through population studies that provided a distribution of results. Moreover, the criteria were binary (reliable versus unreliable) rather than continuous. In this investigation, the authors evaluated visual fields from a very large population of patients and used a multilevel model of longitudinal data to determine the influence of false positives, false negatives, fixation losses and test time on visual field mean deviation (MD) which is often used as an indicator of visual field status in glaucoma. It was found that fixation losses did not influence MD values to any appreciable extent, but false positives elevated MD, and increasing amounts of false negatives and test time decreased MD values. These evidence-based results provide important information for eye care specialists that rely on visual field testing for monitoring glaucoma patients and those at risk of developing glaucoma. In this view, the authors are to be congratulated for providing a well-constructed evaluation of visual field reliability and their influences on test results.

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