Initial Noncontact Intraocular Pressure Readings Artificially High

Intraocular pressure (IOP) measurements have a tendency to decrease when measured repeatedly via noncontact tonometry (NCT), according to a study published in Clinical Ophthalmology. The result brings into question the accuracy of the measurements obtained during the first day of measurement.  

The researchers included 84 eyes of 42 university students (34 women, 8 men) who did not have any eye disease or blood pressure abnormalities. Participants refrained from smoking or exercising prior to any measurements.

IOP was measured 3 times in the right eye and 3 times in the left eye each day for a period of 4 days. Participants were randomly assigned to group A or group B. Group A had their right eye measured first on day 1 and group B had their left eye measured first on day 1. Both groups alternated which eye was measured first on day 2 and continued to alternate throughout the 4-day study. Blood pressure and cardiac rate were also measured at the same time as IOP. 

The investigators noted an average increase in IOP associated with a 10 mm Hg increase in systolic blood pressure of 0.26 mm Hg (95% CI 0.23 to0.28), and an average increase associated with a 5 mm Hg increase in diastolic blood pressure of 0.17 mm Hg (95% CI 0.11 to 0.23).

“The results showed that there was a difference in sequentially measured IOP on day 1, with a tendency toward decreased IOP as the number of measurements increased,” according to the study. “IOP reportedly decreases with repeated measurements, whether during the same day or on different days.” While similar results have been obtained using applanation tonometry, this is one of few studies to report on the accuracy of these measurements using NCT.  

Researchers suggest their results can possibly be attributed to participant nervousness. While no significant changes in participant blood pressure were noted throughout the course of the study, cardiac rate was higher for participants on day 1 than on days 2 through 4. 

Study limitations include the influence of ocular pulse and diurnal IOP fluctuations, a single-center design, a narrow range of ages, and unequal gender distribution of participants. 

Disclosure: Multiple study authors declared affiliations with the biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.  

Reference    

Tatara S, Maeda F, Tsukahara Y, Handa T, Yaoeda, K. Intrasession and intersession variabilities of intraocular pressure measured by noncontact tonometer in normal volunteers. Clin Ophthalmol. 2021; 11(15):4507-4512 doi:10.2147/opth.s342014