Posters

The coefficient of rigidity of the human keratoconic, post cross-linked and normal cornea measured by Schiøtz tonometer

Poster Details

First Author: L.Tutchenko UKRAINE

Co Author(s):    S. Patel   O. Voytsekhivskyy   M. Skovron   O. Horak           

Abstract Details

Purpose:

To determine if differential tonometry, using a Schiøtz tonometer, can distinguish between keratoconic, keratoconic corneas treated by cross-linking to offset progression and normals.

Setting:

Department of Ophthalmology, Shupyk National Medical Academy of Postgraduate Education, Kyiv, Ukraine; Kyiv City Clinical Ophthalmological Hospital “Eye Microsurgery Center”, Ukraine.

Methods:

This was a partially masked randomised study involving keratoconic (A, n=61), post cross-linked cases (post-CXL, B, n=44) and age/gender matched normals (C, n=30). Schiøtz tonometry was performed using 5.5, 7.5, 10.0 & 15.0mgm weights in ascending order. After a 10-minute rest, procedure was repeated in descending order starting with 15.0mgm. All possible combination pairs of data were used to determine the corneal coefficient of rigidity (CoR) of each case value using Friedenwald’s nomogram. Central pachymetry (CCT) was performed using Orbscan II (Bausch & Lomb). The group B cases had previously been treated by CXL (epi-off, 3mW/cm2, 30 min).

Results:

The chief findings (p<0.05) were as follows. 1) Mean (±sd) Schiøtz tonometer scale readings during the ascending phase for the 5.5mgm weight were: A, 6.79(1.73); B, 6.09(2.09); C, 5.42(1.47). 2) The CoR values during the ascending mode using 5.5&10mgm weights, the mean (±sd) CoR values were A, 0.0177(0.0108); B, 0.01629(0.0081); C,0.02587(0.0222). Differences between A&C, B&C were significant but not between A&B. 3) Mean pachymetry values(µ) were A, 453.97(66.29); B, 354.36(70.61); C, 551.40(35.13). Inter-group differences were significant. There was no correlation between response to individual weights or CoR with CCT in each group.

Conclusions:

The traditional method for estimating CoR using Friedenwald’s nomogram could not differentiate between post-CXL and keratoconic corneas. Nevertheless, post-CXL cases responded differently to a Schiøtz tonometer compared with the keratoconics and normals. For a 5.5mgm weighted Schiøtz tonometer and arbitrary cut-off value of 5, the results show the sensitivity and specificity for differentiating between keratoconic and post-CXL cases is 61% and 77% respectively.

Financial Disclosure:

None