What’s relevant: IOP peak or range?
Another question when monitoring IOP concerns the value of using the peak IOP or the range in the patients’ IOP levels, according to Dr. Coleman.
Collaer and associates evaluated 53 patients with normal-tension glaucoma (NTG), 28 with POAG, and 12 glaucoma suspects who had visual field progression despite the fact that the IOPs were controlled in the office.
The investigators performed sequential Goldmann tonometry measurements in the office hourly from 7 a.m. to 5 p.m. during the course of 1 day.
They found that in the patients with NTG, there were significant correlations between the deterioration in the visual fields and the peak IOP (p < 0.001) and with the range of the IOP (p = 0.05).
“However, the peak IOP was the factor that really seemed to be associated with the deteriorating visual fields in this group,” Dr. Coleman said.
Interestingly, not all large population-based studies reach the same conclusions. The Early Manifest Glaucoma Trial reported that inter-visit IOP fluctuations were not an independent risk factor for glaucoma progression.
In contrast, in the Advanced Glaucoma Intervention Study, greater IOP fluctuations were associated with higher odds of visual field progression in patients with a low mean IOP but not in those with a high mean IOP, she noted.
“This indicates that there are some differences in terms of the types of patients being evaluated and how much IOP fluctuations play a role,” Dr. Coleman said.
The take-home message regarding the challenge of setting the target IOP for patients is that knowledge about IOP variations is important, she noted.
“This knowledge can help set the target IOP, but clinicians must be aware of the degree of the IOP variations,” Dr. Coleman said. “This requires follow-up and frequent diurnal measurements in the office, which most clinicians are no longer doing.”
It can be difficult initially to use IOP fluctuations to set the target IOP, but the variations can be used to help modify the chosen target IOP while patients are being followed to ascertain that the glaucoma is not progressing and that the damage remains stable, she concluded.
Dr. Coleman advised that further research be performed to understand how the 24-hour IOP parameters—i.e., peak IOP, mean IOP, and fluctuations—might be predictive of disease progression.