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Assessing Early Stage Open-Angle Glaucoma in Patients by Isolated-Check Visual Evoked Potential
Published on: May 25, 2020
Measurement error of visual field tests in glaucoma
P G D Spry1, C A Johnson, A M McKendrick
1Discoveries in Sight, Devers Eye Institute, Portland, OR, USA. paul.spry@ubht.swest.nhs.uk
The British Journal of Ophthalmology
|December 19, 2002
Summary
Staircase visual field testing algorithms used in clinical settings introduce measurement errors, particularly Standard Automated Perimetry (SAP) which overestimates sensitivity in damaged areas of the visual field.
Area of Science:
- Ophthalmology
- Visual Neuroscience
- Medical Technology
Background:
- Clinical visual field testing employs psychophysical strategies for rapid threshold estimation, balancing test quality with efficiency.
- Standard Automated Perimetry (SAP) and Frequency Doubling Perimetry (FDP) are common methods, but their accuracy can be influenced by the algorithms used.
Purpose of the Study:
- To evaluate the measurement error of a staircase algorithm, similar to full threshold, used in SAP and FDP for glaucoma patients.
- To compare the accuracy and precision of SAP and FDP using a specific staircase strategy.
Main Methods:
- Seven early open-angle glaucoma patients underwent testing at three locations using SAP and FDP.
- A 4-2-2 dB staircase strategy was employed, with each location tested twice.
- Thresholds were compared against measurements from the method of constant stimuli (MOCS) to quantify accuracy and precision.
Main Results:
- Both SAP and FDP showed high precision, with FDP being more precise at lower sensitivity levels.
- The staircase strategy significantly underestimated true threshold sensitivity for both tests.
- Mean differences between staircase and MOCS thresholds were 4.48 dB for SAP and 1.35 dB for FDP.
- Agreement (weighted kappa) was 0.48 for SAP and 0.85 for FDP, indicating better agreement for FDP.
Conclusions:
- Staircase algorithms in clinical visual field testing introduce measurement errors that vary by test type and visual field sensitivity.
- Standard Automated Perimetry (SAP) significantly overestimates sensitivity, especially in damaged areas, necessitating cautious interpretation of clinical data.
- Frequency Doubling Perimetry (FDP) demonstrated better accuracy and agreement with the method of constant stimuli compared to SAP.
