Clinical evaluation of the Oculus Keratograph

To determine the validity and reliability of the measurement of corneal curvature and non-invasive tear break-up time (NITBUT) measures using the Oculus Keratograph.

One hundred eyes of 100 patients had their corneal curvature assessed with the Keratograph and the Nidek ARKT TonorefII. NITBUT was then measured objectively with the Keratograph with Tear Film Scan software and subjectively with the Keeler Tearscope. The Keratograph measurements of corneal curvature and NITBUT were repeated to test reliability. The ocular sensitivity disease index questionnaire was completed to quantify ocular comfort.

The Keratograph consistently measured significantly flatter corneal curvatures than the ARKT (MSE difference: +1.83 ± 0.44D), but was repeatable (p > 0.05). Keratograph NITBUT measurements were significantly lower than observation using the Tearscope (by 12.35 ± 7.45 s; p < 0.001) and decreased on subsequent measurement (by -1.64 ± 6.03 s; p < 0.01). The Keratograph measures the first time the tears break up anywhere on the cornea with 63% of subjects having NITBUTs <5 s and a further 22% having readings between 5 and 10 s. The Tearscope results were found to correlate better with the patients symptoms (r = -0.32) compared to the Keratograph (r = -0.19).

The Keratograph requires a calibration off-set to be comparable to other keratometry devices. Its current software detects very early tear film changes, recording significantly lower NITBUT values than conventional subjective assessment. Adjustments to instrumentation software have the potential to enhance the value of Keratograph objective measures in clinical practice.