Visual field tests every 6 months optimal for high-risk patients with ocular hypertension
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Key takeaways:
- Visual field tests are warranted every 6 months in high- and medium-risk patients with ocular hypertension.
- To reduce the burden of office visits, low-risk patients can be tested every 12 months.
Patients with ocular hypertension may undergo visual field tests every 6 months if they are at high or medium risk for progression to primary open-angle glaucoma, and every 12 months if they are at low risk, according to a study.
The study, published in the Journal of Glaucoma, used computer simulations to calculate the time it would take for different intervals of visual field (VF) testing to detect rapidly progressing, clinically meaningful perimetric loss.
Drawing on data from the Ocular Hypertension Treatment Study (OHTS), researchers found that the 6-month interval used in that study was optimal, though low-risk patients could be seen every 12 months.
The finding could ease the burden of frequent office visits, especially in low-risk patients, and sheds light on how frequently patients with untreated ocular hypertension should be examined for progression to primary open-angle glaucoma (POAG), researchers wrote.
Participants from OHTS phase 1 with more than five visits and 2 years of follow-up data were divided into three groups based on a calculation of their 5-year risk for developing POAG.
For each group, a Stata 16 simulation estimated the time to detect a rapid rate of VF progression — defined as –0.42 dB/year — at 80% power and intervals of 4, 6, 12 and 24 months. Researchers also calculated the time for each group to reach a clinically meaningful perimetric loss (CMPL), defined as –3 dB.
In each risk group, detection time decreased by about 18% by testing every 6 months vs. every 12 months, as well as every 12 months vs. every 24 months. There were fewer reductions — around 11.5% in each risk group — by testing every 4 months vs. every 6 months.
Shorter testing intervals of 6 months were necessary for detecting CMPL in high- and medium-risk patients. The findings suggest a 12-month interval for low-risk patients, because “long-term results from OHTS demonstrated that only one-fourth of patients showed evidence of VF loss in either eye, whereas the low-risk patients presented with a cumulative POAG incidents of 31.7%,” researchers wrote.
The study’s limitations included its use of an arbitrary estimate of –3 dB for CMPL. Researchers also noted their use of a global, trend-based method of detecting glaucoma progression, which could miss a conversion to glaucoma that a pointwise, event-based approach would catch.
The study authors wrote that based on their findings, “clinicians may choose the best interval for repeating the VF test, taking into account each patient’s risk factors.”
Perspective
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Selecting an appropriate interval for perimetric testing in ocular hypertensive glaucoma suspects is critical for earlier detection of glaucoma, but evidence regarding the frequency at which testing should occur in this group is lacking.
While this model would support biannual testing in medium- and high-risk glaucoma patients, it is worth mentioning that the times to reach the cutoff were considerable, ranging from 6 to 8.5 years in the 6- and 12-month interval analysis for all levels of risk of conversion. In addition, testing at 4-month intervals showed only a modest increase in time-to-detect over the 6-month interval across all risk groups, implying there is a saturation point with this model.
More importantly, as the authors state, these times reflect only the time it would take for a rapid rate of progression (–0.42 dB/year) to reach the threshold of –3 dB and do not incorporate the pointwise perimetric events or any structural assessments that might indicate glaucoma.
Nonetheless, the argument for biannual perimetric testing in high- and medium-risk ocular hypertensives is worth considering, as the pointwise analysis is also likely improved by shortening testing intervals.
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