Applanation Tonometry and Central Corneal Thickness

Abstract

Readings with the Goldmann applanation tonometer were made at various intraocular hydrostatic pressures and compared with central corneal thickness and radius in rabbit and in man. Linear correlations were established between hydrostatic pressure and applanation readings, with correlation coefficients close to 1.0. In rabbits the tonometer readings were generally too low. In human eyes with a normal corneal thickness tonometer readings and hydrostatic pressure coincided, with thick corneas the readings were too high, with thin corneas too low. The correlation between corneal thickness and the error of applanation tonometry (LIP) was statistically highly significant (P < 0.001). No statistical correlation could be established between corneal radius and AP. Multiple regression, taking thickness as well as corneal radius into consideration, revealed only slightly higher correlation coefficients. It is concluded that the central corneal thickness is a parameter which should be taken into consideration when evaluating applanation tonometer readings. A Table is presented showing the correction to be added to the applanation reading at differing corneal thickness. A clinical study of the normal human central corneal thickness. Kruse Hansen, F. PC Ehlers, N. (1971) Elevated tonometer readings caused by a thick Mishima, S. & Hedbys, B. 0. (1968). Measurement of corneal thickness with the Haag-Acta ophthal. (Kbh.) 49, 82-89. cornea. Acta ophthal. (Kbh.) 49, 775-778. Streit pachometer. Arch. Ophthal. (Chicago) 80, 710-7 13.

Increased intraocular pressure on the first postoperative day following resident-performed cataract surgery

“…46 It is well known that thicker cornea in non-surgical patients causes an overestimation of IOP measured by applanation tonometry. [47][48][49] However, as the measurements compared preoperative with postoperative IOP for each individual patient rather than the mean between groups, the corneal pachymetry will have a lesser role in the variability of the values.…”

Corneal hysteresis in patients with dry eye

“…GAT measured IOP accurately when CCT was 520 mm, and each 10% difference of CCT would result in 1.1 mm Hg differences in IOP. [18][19][20] In this study, the correlation between CH and IOPcc was also searched. There was a positive correlation and this is statistically significantly different (Pearson correlation test, r ¼ 0.466, Pr0, 05).…”

Comparison of three methods of intraocular pressure measurement and their relation to central corneal thickness

“…5 It is well known that GAT is affected by the central corneal thickness (CCT). 6,7 The Ocular Hypertension Treatment Study showed that CCT is an important and independent risk factor for the progression of ocular hypertension to a first diagnosis of glaucoma. 8 It has been estimated that a measurement error of between 0.11 9 and 0.71 mmHg 7 occurs per 10 mm deviation from the average CCT of 550 mm.…”