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D.C. Pye, K.E. Hamilton; True Intraocular Pressure and Young's Modulus of the Cornea May Vary With Corneal Thickness in vivo . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4450.
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© ARVO (1962-2015); The Authors (2016-present)
Variations in corneal thickness are believed to cause an error in intraocular pressure (IOP) measurement by the Goldmann tonometer. The aim of this study was to determine whether the calculated true IOP and Young’s modulus of the cornea varies with corneal thickness in young adult humans in vivo.
Central corneal curvature (Reichert EyeChek autokeratometer), central corneal thickness (BVI ultrasonic pachymeter) and applanation IOP (Goldmann tonometer) were measured in 99 right eyes of normal healthy human subjects (21.1±2.9 y) in vivo. The algorithms of Doughty and Zaman, Ehlers et al., Orssengo and Pye, Whitacre et al. and the Dresden correction table were used to correct the applanation IOP for the effects of corneal thickness. Young’s modulus of the cornea was calculated using the Orssengo–Pye algorithm.
The mean central corneal curvature of the subjects was 7.8 mm (95% CI 7.2–8.3 mm), central corneal thickness was 547.3 µm (95% CI 480.5–614.0 µm) and applanation IOP was 15.2 mmHg (95% CI 9.8–20.6 mmHg). There was no statistically significant Pearson correlation between the corneal thickness and Goldmann applanation IOP (R=0.007, p=0.945). Linear regression revealed a statistically significant negative relationship between corneal thickness and the corrected IOP for all algorithms: Doughty and Zaman (–0.62 mmHg/10 µm), Ehlers et al. (–0.62 mmHg/10 µm), Orssengo–Pye (–0.38 mmHg/10 µm), Whitacre et al. (–0.20 mmHg/10 µm) and the Dresden correction table (–0.41 mmHg/10 µm). All slopes were statistically significant (p<0.05). Young’s modulus of the cornea decreased with increasing corneal thickness at a rate of 7.51 kPa/10 µm (R=0.426, p<0.001, linear regression).
The results suggest that, in healthy young humans in vivo, the true IOP and Young’s modulus of the cornea may decrease as corneal thickness increases.
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