Evaluation of the EyeSys model II computerized videokeratoscope. Part I: Clinical assessment

To compare the agreement and repeatability of keratometry measurements with simulated keratometry measurements from the EyeSys (model II) corneal analysis system (CAS). Furthermore, to establish any relationship between the repeatability of peripheral corneal measurements and the spatial location at the cornea.

Measurements using a Bausch & Lomb keratometer in 19 eyes (19 subjects) were compared with the simulated keratometry values using the EyeSys CAS. Repeatability of the keratometer (14 eyes, 14 subjects) and the EyeSys simulated keratometry values (10 eyes, 10 subjects) was assessed by comparing the difference of two measurements. Peripheral repeatability of the EyeSys CAS was compared in a similar manner in a sample of 10 eyes (10 subjects).

The 95% confidence limits (-0.529 to +0.149 D) showed a lack of agreement between both instruments. With respect to the repeatability, both the keratometer (SD = +/- 0.103 D) and the EyeSys (SD = +/- 0.072 D) were found to exhibit approximately similar degrees of repeatability. The repeatability of peripheral corneal measurements using the EyeSys CAS showed changes in repeatability dependent on the corneal meridian and the distance from the point of alignment. Measurements along the superior and nasal meridians showed poorest repeatability. Repeatability was also found to deteriorate away from the point of alignment.

EyeSys simulated keratometry values were not interchangeable with the keratometer. This could be due to differences in the method of alignment or measurements from different areas on the corneal surface. Repeatability of both the Bausch & Lomb keratometer and the EyeSys CAS was found to be similar. The spatial dependency of peripheral corneal radius repeatability measurements could be attributed to interference of the ocular adnexa in those areas of measurement.