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Pay attention to examination quality
- Examinations of poor quality will likely lead to an erroneous assessment of progression.
Comment: The most important factors to reduce test variability are a proper explanation of the test to the patient, appropriate instrument setup and 1:1 monitoring of the patient by a trained technician.
- Do not rely automatically on the VF reliability indices.
Comment: The VF reliability indices may be unreliable! The most useful index is the ‘False Positive’ rate; values greater than 15% likely represent a less reliable performance; values less than 15% do not guarantee reliability. The technician is the best judge to exam quality.
- If unreliable tests require repeating, the patient should be carefully re-instructed.
Use the same threshold test
- Clinicians should select their preferred perimetry technology, test pattern, and thresholding strategy for the baseline tests and stick with the same test throughout the follow up.
Comment: any analysis of progression can only be performed if a compatible threshold algorithm and test pattern is used.
- In advanced glaucoma, smaller angular size SAP testing grids, e.g., HFA 10-2 may be of value in a minority of patients.
Comment: Kinetic perimetry and SAP with larger targets (e.g., size V) may also be useful.
Comment: The advantages of a change in test pattern (e.g., from a 24-2 to a 10-2 grid) should also be weighed against the disadvantages for progression analysis by commercial software.
Clinical trials
- Event analyses aim to identify a statistically significant difference between study arms and not necessarily a clinically significant difference.
Comment: As glaucoma is a chronic progressive disease and progression is generally linear, small amounts of progression that reach statistical significance become larger, clinically significant amounts of progression if there is no additional therapy.
- Rate analyses of VF indices are an appropriate statistical approach to identify differences between treatment groups.
Comment: Rate analysis methods have been used often in trials for other chronic progressive diseases, such as dementia.
- Difference in the progression ‘event’ criterion applied in the various clinical trials limits comparison of the incidence of progression determined in those trials.
Comment: Comparison of groups in different clinical trials is also hampered by mismatch of subjects with regard to stage of glaucoma, quality of visual field exams, and other traits.
Research needs
- The development of ‘event’ criteria for progression based on individual patient test-retest variability.
- There is a need to compare event-based endpoints and rate of progression outcomes in a data set with data acquired with appropriate frequency and test intervals with respect to clinical trials.
- Further research is needed into the added value of smaller angular size test grids, and different size stimuli, e.g., size V, in advanced glaucoma.
- Determine appropriate dynamic ranges of stimulus contrasts for size III, and develop new stimuli with larger dynamic ranges of appropriate stimulus contrasts.
- Improve the interface between perimetrist and device, and between patient and device.
- Identify, or develop, stimulus types (e.g., FDT) and test algorithms which provide optimal information content for progression analysis in children and adults who have difficulty performing a reliable SAP test.
- Develop alternate methods for selecting stimulus locations in order to avoid extensive testing of blind areas and to focus on areas of interest.
- Further assess the benefits of using prior threshold as a starting point in a follow-up test (or if threshold is < 0 dB previously, confirmation at that point that a 0 dB stimulus is not seen is sufficient).
- Determine the optimal frequency and timing of tests for individual patients.
- Use of good mathematical modeling.
- Develop better approaches to identify learning effects.
- Identify the appropriate test and frequency of testing for patients with progressive glaucomatous optic neuropathy and SAP within normal limits.
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