Association found between office-hour, peak nocturnal IOP readings
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Researchers observed a link between office-hour IOP and peak nocturnal IOP in a group of patients with primary open angle glaucoma and ocular hypertension, according to a study published in the American Journal of Ophthalmology.
“There is a correlation between office-hour IOP reading and peak nocturnal IOP in this group of prostaglandin analogs-treated patients with glaucoma and ocular hypertension,” Diya Yang, MD, PhD, from the Shiley Eye Institute at the University of California and the Beijing Tongren Eye Center in the Beijing Institute of Ophthalmology at Beijing Tongren Hospital at Capital Medical University in Beijing, and colleagues wrote. “However, the correlation is less than what occurs without IOP-lowering medication.”
Fifty-one patients (22 with open angle glaucoma, 29 with ocular hypertension) were included in this study. Baseline 24-hour IOP was measured every 2 hours using a pneumotonometer in the sitting and supine position during the diurnal/wake period (7:30 a.m. to 9:30 p.m.) and the supine position during the nocturnal/sleep period (11:30 p.m. to 5:30 a.m.). Researchers analyzed individual and average IOP during office hours (9:30 a.m. to 3:30 p.m.). Patients did not receive IOP-lowering medication.
After baseline, patients received latanoprost (n = 18), travoprost (n = 17) or bimatoprost (n = 16) every day for 4 weeks with 24-hour IOP measurements performed in the same preparation and laboratory procedures.
Results showed statistically significant correlations for all variables in the analysis. Average office-hour IOP reading showed a higher correlation with peak nocturnal IOP than individual office-hour IOP. Under no IOP-lowering treatment, nocturnal peak IOP was significantly correlated with individual office-hour IOP in sitting (r = 0.462) and supine positions (r = 0.510).
After receiving IOP-lowering treatment, the correlation coefficients were reduced in office-hour sitting (r = 0.34) and office-hour supine (r = 0.336). When analyzing average office-hour IOP, there was a high correlation between nocturnal peak IOP in office-hour sitting (r = 0.517) and office-hour supine (r = 0.386).
“The weaker correlation under prostaglandin analogs treatment may be due to various factors associated with the 24-hour IOP pattern and the IOP-lowering medication that was administered,” the researchers wrote. “One should be more cautious with the use of office-hour IOP readings to predict the nocturnal IOP level in treated patients than in patients under no treatment.”
Perspective
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Derek MacDonald, OD, FAAO
It’s been said that glaucoma is a 24-hour (perhaps even nocturnal) disease that we try to manage over 8 (office) hours of the diurnal period.
We know that most patients experience their peak IOP at night, and the negative impact of that spike may be compounded by a decrease in systemic blood pressure that compromises ocular perfusion pressure. We also know that accurately measuring nocturnal IOP, particularly in a supine position, is very difficult in a dedicated sleep lab, let alone an office environment. Further, the already modest correlation between in-office and nocturnal IOP in untreated eyes is weakened by treatment, primarily because of the relatively greater diurnal impact of most medications, leading Yang and colleagues to caution against predicting nocturnal IOP from diurnal measurements in treated patients.
However, it is interesting and logical to note that the 24-hour variability of supine IOP is significantly less than that of habitual (daytime upright and nighttime supine) IOP. Particularly in patients who are progressing at target IOPs, consideration may be given to obtaining supine early- to mid-morning tonometry readings. You may be surprised at what you find and change your management as a result.
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