Repeatability And Agreement Of Chord Mu Using Scheimpflug Tomography And Optical Coherence Reflectometry In Myopes And Keratoconus

To assess the repeatability and agreement of Chord mu using Scheimpflug tomography and Optical Coherence Reflectometry in Myopes and Keratoconic population

Wagh Eye Clinics

30 patients (60 eyes) in each group fulfilling inclusion and exclusion criteria underwent subjective refraction, slit lamp examination and three measurements using Oculyzer II (Oculus Optikgeräte GmbH, Wetzlar, Germany)  and Lenstar (Lenstar LS 900, HAAG-STREIT AG, Switzerland). Outcome measures were X and Y Cartesian distance (the distance between the corneal vertex and the pupil center, Px and Py), pupil diameter, and chord mu. Oculyzer II, and the Lenstar 900 provides only Px and Py values. Thus, chord mu measured by these instruments was calculated using the formula “r = (X² + Y²)^1/2

In both groups , the ICC values for x, y, Chord mu, pupil diameter were excellent for the Oculyzer and Lenstar. In the myopic group, while comparing the two devices, the correlation was strong for all parameters as per the Pearsons correlation coefficient (r > 0.5). However, the difference between the mean values for all parameters except the x value were statistically significant. In Keratoconus group, when comparing the two devices, the correlation was strong for all parameters except pupil diameter and y values. The differences between the mean for x and Chord mu values were found to be statistically significant (p > 0.05) between these 2 devices.

The Oculyzer and Lenstar showed good repeatability and agreement for Chord Mu in Myopic and Keratoconic eyes. However, the mean differences between the parameters were statistically significant which suggests that these devices may not be used interchangeably for assessing chord mu and pupil diameter.