Elsevier

Ophthalmology

Volume 105, Issue 10, 1 October 1998, Pages 1849-1854
Ophthalmology

Positive correlation between Tono-pen intraocular pressure and central corneal thickness

https://doi.org/10.1016/S0161-6420(98)91029-6Get rights and content

Abstract

Objective

To examine the relationship between intraocular pressure (IOP) readings taken by the Tono-Pen tonometer (Mentor O&O, Norwell, MA) and central corneal thickness (CCT).

Design

Prospective cross-sectional population study.

Participants

There were 651 eyes of 332 healthy subjects.

Main outcome measures

A questionnaire was given to each subject requesting information on gender, age, race, and other factors that can influence IOP. The IOP then was measured using the Tono-Pen followed by measurements of CCT using an ultrasonic pachymeter.

Results

The IOP was found to increase by 2.9 mmHg/100 μm CCT in males and 1.2 mmHg/100 μm in females. For males, CCT was found to be statistically significant in predicting IOP (P < 0.001 in the right and left eyes) and diabetes was of borderline significance (P = 0.012 in the right eye, P = 0.089 in the left eye). For females, CCT was of borderline significance (P = 0.064 in the right eye, P = 0.019 in the left eye). In females, a family history of glaucoma (P = 0.021 in the right eye, P = 0.022 in the left eye) and hypertension (P = 0.010 in the right eye, P = <0.001 in the left eye) were also significant in the prediction of IOP. Race was found to be a significant predictor of CCT (P < 0.001 in both right and left eyes) for both males and females.

Conclusion

Clinicians should be aware that, as with the Goldmann applanation tonometer, the Tono-Pen has a systematic error in IOP readings caused by its dependence on CCT. Tono-Pen IOP readings are positively correlated to CCT in males and, to a lesser extent, in females as well. The CCT measurements should be considered to ensure proper interpretation of IOP measurements in the diagnosis and management of disorders in which the CCT or IOP readings are outside normal limits.

Section snippets

Methods

A prospective study was conducted at four public buildings (3 malls, 1 hospital) between 9 am and 4 pm as part of an eye health information and glaucoma-screening program. Participation was strictly voluntary, and all individuals who were willing to be tested were included. Initially, each participant filled out an anonymous questionnaire that asked for information pertaining to possible risk factors and exclusion criteria (Fig 1).

Subjects were then given topical anesthesia (Alcaine; Alcon, Ft.

Results

A total of 351 subjects were tested in the screening protocol. Subjects were excluded from the study if they were diagnosed with glaucoma (n = 7), were wearing contact lenses (n = 7), had no CCT or IOP measurements for both eyes (n = 3), had prior eye trauma (n = 1), or had pseudophakos (n = 1). In total, 19 of 351 subjects were excluded completely from the study. Of the remaining 332 subjects, 651 eyes were included in the study. Some eyes (5 right and 8 left) were excluded because prior

Discussion

Previous investigators have reported on the relationship between CCT and measured IOP for Goldmann applanation tonometry.1, 2, 3, 4, 10, 11 The Goldmann tonometer has been calibrated for a CCT of approximately 0.52 mm and will tend to overestimate IOP in structurally thicker corneas and underestimate IOP in thinner corneas. In corneas with a CCT greater than 0.52 mm, this systematic error in IOP measurement is related to more corneal rigidity due to the increased CCT. This increase in rigidity

Acknowledgements

The authors thank Mentor Canada for supplying the Tono-Pens used in this study.

References (29)

  • F.K. Hansen

    A clinical study of the normal human central corneal thickness

    Acta Ophthalmol (Copenh)

    (1971)
  • N. Ehlers et al.

    Applanation tonometry and central corneal thickness

    Acta Ophthalmol (Copenh)

    (1975)
  • V. Hessemer et al.

    Tono-Pen, a new tonometer

    Int Ophthalmol

    (1989)
  • J.A. Khan et al.

    Comparison of Oculab Tono-Pen readings obtained from various corneal and scleral locations

    Arch Ophthalmol

    (1991)
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