Intra-Ocular Pressure Measurement in a Patient with a Thin, Thick or Abnormal Cornea

Abstract

Accurate measurement of intra-ocular pressure is a fundamental component of the ocular examination. The most common method of measuring IOP is by Goldmann applanation tonometry, the accuracy of which is influenced by the thickness and biomechanical properties of the cornea. Algorithms devised to correct for corneal thickness to estimate IOP oversimplify the effects of corneal biomechanics. The viscous and elastic properties of the cornea influence IOP measurements in unpredictable ways, a finding borne out in studies of patients with inherently abnormal and surgically altered corneal biomechanics. Dynamic contour tonometry, rebound tonometry and the ocular response analyzer provide useful alternatives to GAT in patients with abnormal corneas, such as those who have undergone laser vision correction or keratoplasty. This article reviews the various methods of intra-ocular pressure measurement available to the clinician and the ways in which their utility is influenced by variations in corneal thickness and biomechanics.

A comparison of NCT, Goldman application tonometry values with and without fluorescein

“…In clinical practice, Goldmann applanation tonometry (GAT) is the gold standard and the most widely method for measuring IOP. 11 , 12 Noncontact tonometer (NCT) is a commonly used method in IOP measurement, and works following similar principles with GAT without the need for topical anesthetics. NCT is well correlated with GAT.…”

A comparison of intraocular pressure values obtained using a Goldmann applanation tonometer and a handheld version of applanation resonance tonometer: A preliminary report

“…Goldmann applanation tonometry is a tonometer calibrated to the mean corneal thickness -520 nm, thus, it is not accurate for every type of the cornea. 3 The studies show that the values of IOP measured by GAT are underestimated in patients after refractive eye surgery, and the number of those patients is still increasing. It was proven that ablation of the center of the cornea results in a constant decrease of IOP values by approx.…”

Intraocular Pressure Measurement by Goldmann Applanation Tonometer and Noncontact Tonometers Taking Consideration of Central Corneal Thickness- A Comparative Cross-Sectional Study

“…A thinner cornea may require lesser force to applanate it leading to underestimation of the IOP and vice versa. 2 There is also evidence that central corneal thickness and IOP also changes on day and night cycle. 3 An alternative method, in which corneal applanation is produced by an air pulse, so called 'noncontact' tonometry.…”