A cross-sectional study published in Clinical and Experimental Optometry revealed a pilot model for 10-2 visual field (VF) testing.
Give me some background first.
The 24-2 test grid is commonly used in clinical practice to cover field defects that are typically affected by glaucoma.
The central visual field is also important in glaucoma; defects in this area often indicate the disease has progressed to its more advanced stages.
However, there are conflicting reports regarding the relative effectiveness of 24-2 in comparison to the 10-2 test grid for identifying central VF defects.
Got it. Now talk about the study.
Investigators gathered sensitivity results, probability scores, and global indices from the 24-2 and 10-2 test grids to compare the dynamic range between the respective VF test grids.
And the participants?
A total of 133 eyes from 133 glaucoma patients from the Center for Eye Health, University of New South Wales were observed.
All participants must have met the reliability criteria for the 10-2 (SITA-FAST) and 24-2 (SITA-FASTER) VF data.
Patients with the following characteristics were excluded:
- Less than 18 years old
- History of ocular trauma or surgery
- Any macular, retinal, or neurological pathology that may affect VF measurement
- Dense cataracts that impact integrity of the VF
Describe the functional vulnerability zone model.
The functional vulnerability zone (FVZ) is a zone of VF that can be identified on the 10-2 grid, but not on the 24-2 grid.
An FVZ indicates to clinicians that the 10-2 test grid may provide additional information compared to the 24-2 about a glaucoma patient.
How were FVZs used?
Researchers identified three possible FVZ outcomes in this study:
- The 24-2 and 10-2 defects are identical (no FVZ).
- The 10-2 provides no additional information due to the depth of the defect (no FVZ).
- The 10-2 locations have a higher sensitivity result than the predicted slope and provide additional information (FVZ present).
In outcomes 1 and 2, the 10-2 test grid will not provide any additional information, though it can be used to confirm findings from the 24-2 test grid.
In outcome 3, there are areas that can only be found using the 10-2 test grid.
Findings?
Patients exhibiting a more positive mean deviation in the 10-2 test with proportionally fewer defects compared to the 24-2 were more likely to have an FVZ.
To note, though, not all subjects were found to have an FVZ. Because of this, the 10-2 test grid provided little useful information regarding dynamic range.
Tell me more.
The study authors proposed three instances in which the 10-2 VF field may maximize dynamic range:
- Identification of five or more defective locations in the central VF in the 24-2
- Mean deviation of 10-2 is less severe relative to the 24-2
- Less than four affected 10-2 locations per one 24-2 test location with a defect
Limitations?
More data is needed to test the external validity of this pilot study. After years of data have been produced, a longitudinal analysis may be completed to compare results over time. It is also beneficial to include more repeatable test data, which was not the focus of this study.
Only the most common test grids on the Humphrey Field Analyzer—the 24-2 and 10-2—were analyzed in this study. Further research on other test grid assessments will provide more depth regarding optimal test grid usage.
Take home.
This pilot study provides a framework proposing indicators for maximal use of the 10-2 test grid in clinical settings. Additional data can further develop this model for the greater benefit of clinical examination of glaucoma.