When setting a target IOP for patients with glaucoma, consideration of IOP fluctuations and the degree to which they vary is important.
Reviewed by Anne Louise Coleman, MD, PhD
All areas of medicine are undergoing important innovations, and the primary movement is in the direction of individualized medicine.
This individualization also is evident to the clinical level, where consideration is being given to personalizing IOP levels in patients with fluctuating IOPs and using diurnal IOP fluctuation data to treat glaucoma and set target pressures.
The American Academy of Ophthalmology Preferred Practice Pattern recommends a blanket approach to IOP reduction-i.e., that the IOP should be reduced by 20% to 30% in order to avoid damage to the visual fields in patients with primary open-angle glaucoma (POAG) followed by monitoring of the structure and function of the optic nerve if treatment adjustments are needed.
With this generalized approach, the challenge is determining the appropriate target IOP, according to Anne Louise Coleman, MD, PhD.
“When setting the target pressure, there are many factors to consider, and unfortunately, the percent reduction might not always be 20% to 30%,” said Dr. Coleman, the Fran and Ray Stark Foundation Professor of Ophthalmology, Stein Eye Institute, David Geffen School of Medicine, UCLA, Los Angeles.
“Clinicians must consider the type of glaucoma, visual field loss, nerve damage, progression rate, corneal properties, and the risk profile that includes age, race, family history, and IOP fluctuations,” she added.
A caveat regarding management of IOP is that clinicians should not put all of their stock into one IOP measurement, despite the fact that the population-based and epidemiologic glaucoma studies view one measurement as important and reliable.
A one-time IOP measurement can be misleading and can be a poor indicator for diagnosis and treatment, Dr. Coleman noted.
In individual patients, the IOPs, like blood pressure, can vary substantial from one hour to the next and from one day to the next because of the measurement reproducibility, patient activity levels, fluid intake, body position, and circadian rhythm.
“Many factors can influence that one-time pressure reading,” she said.
Large fluctuations in IOP seem to be a risk factor for progression of visual field damage.
Dr. Coleman cited a study by Asrani and colleagues (J Glaucoma. 2000;9:134-142) that evaluated 64 patients with POAG who measured their IOP at home five times daily for 5 days during waking hours. All patients had an IOP under 25 mm Hg and were followed for a minimum of 1 year (mean, 5 years).
“The investigators found that larger pressure fluctuations were a risk factor for visual field progression that was independent of all the parameters that were obtained in the office including the baseline IOP and visual field damage,” Dr. Coleman said.
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.
Anne Louise Coleman, MD, PhD
This article was adapted from Dr. Coleman’s presentation at the 2016 meeting of the American Academy of Ophthalmology. Dr. Coleman has no financial interest in any aspect of this report.