Posterior corneal curvature changes in patients with keratoconus

Session Details

Session Title: Corneal Biomechanics

Session Date/Time: Sunday 15/09/2019 | 16:30-18:00

Paper Time: 17:18

Venue: Free Paper Forum: Podium 4

First Author: : N.Menassa UK

Co Author(s): :    M. Brunner   C. de Lossada   D. Borroni   G. Czanner   S. Kaye   V. Romano              

Abstract Details

Purpose:

To investigate a method for precision analysis to discriminate corneal change from measurement imprecision in patients with keratoconus (KC).

Setting:

St. Paul's Eye Unit, Royal Liverpool University Hospital, Liverpool, United Kingdom

Methods:

Patients with KC and healthy controls were included in a prospective study. Posterior corneal tomographic parameters using a Pentacam HR were analysed. Patients had 3 measurements undertaken on 2 occasions. Coefficients of repeatability and limits of agreement (LOA) were compared using single and multiple measurements for each observer. Correlation of repeated measurements was evaluated using a linear mixed effect model. A formula was derived for the theoretical expected change in precision and compared with measured change.

Results:

Sixty eyes of sixty patients were included: 30 healthy subjects (mean age 31.6±10 years) and 30 patients with KC (mean age 26.7±8 years). High quality scans were achieved in all healthy eyes (180 scans) and in 91.7% of the keratoconic eyes (165 scans). Posterior corneal curvature values were significantly higher in the KC group (p<0.01). Intra- and inter-observer 95% and 99.73% limits of agreement (LOA) for K1 flat [D], K2 steep [D], K mean [D], and K2-K1 [D] in healthy and keratoconic eyes showed 99.73% LOA using mean of 3 measurements were narrower than one-measurement 95% LOA.

Conclusions:

The 99.73% LOA (3 SD) using the mean of three measurements, provides better precision than 95% LOA (2 SD) using a single measure. A change in the back surface of the cornea of more than 0.21D K1 or 0.17D K2 using the mean of 3 measurements can be used as a cut-off for change in the back surface of the cornea in patients with KC.

Financial Disclosure:

None