Potential effects of systematic errors in intraocular pressure measurements on screening for ocular hypertension

Abstract

Aim Raised intraocular pressure (IOP) increases the risk of glaucoma. Eye-care professionals measure IOP to screen for ocular hypertension (OHT) (IOP421 mm Hg) and to monitor glaucoma treatment. Tonometers commonly develop significant systematic measurement errors within months of calibration, and may not be verified often enough. There is no published evidence indicating how accurate tonometers should be. We analysed IOP measurements from a population study to estimate the sensitivity of detection of OHT to systematic errors in IOP measurements. Methods We analysed IOP data from 3654 participants in the Blue Mountains Eye Study, Australia. An inverse cumulative distribution indicating the proportion of individuals with highest IOP421 mm Hg was calculated. A second-order polynomial was fitted to the distribution and used to calculate over-and under-detection of OHT that would be caused by systematic measurement errors between À 4 and þ 4 mm Hg. We calculated changes in the apparent prevalence of OHT caused by systematic errors in IOP. Results A tonometer that consistently under-or over-reads by 1 mm Hg will miss 34% of individuals with OHT, or yield 58% more positive screening tests, respectively. Tonometers with systematic errors of À 4 and þ 4 mm Hg would miss 76% of individuals with OHT and would over-detect OHT by a factor of seven. Over-and under-detection of OHT are not strongly affected by cutoff IOP. Conclusion We conclude that tonometers should be maintained and verified at intervals short enough to control systematic errors in IOP measurements to substantially less than 1 mm Hg.

Novel dynamic corneal response parameters in a practice use: a critical review

“…Error values vary and depend especially on the accuracy and reliability of the operator’s (ophthalmologist) work. These errors range from a few to several percents [105].…”

Evaluation of a new rebound tonometer for self-measurement of intraocular pressure

“…Using data from the Blue Mountains Eye Study, it was shown that 34% of individuals with ocular hypertension (OHT) would be missed using a tonometer that underestimated IOP by 1 mm Hg. Conversely, 58% false-positive screening tests would occur using a tonometer that over-read by 1 mm Hg 5. Within-subject variation may also contribute.…”

Aktueller Stellenwert der Druckmessung: Messverfahren und Fehlerquellen

“…B. nach LA-SIK, wo sich abhängig vom verwendeten Ablationsprofil noch weitaus größere Abweichungen ergeben können [19,20] oder etwa bei Keratokonus [21]. Eine Unsicherheit ergibt sich auch aus den zahlreichen, mittlerweile gebräuchlichen Messverfahren für die zentrale Hornhautdicke, die nur bis zu einem gewissen Grad mit der von Kohlhaas [22]. In der klinischen Praxis wurden Kalibrierungsfehler von 1 bis 3 mmHg berichtet [23,24].…”