Validation of a handheld automated keratometer in adults

To evaluate the Nidek handheld automated keratometer and compare it with the manual Zeiss keratometer.

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

Forty-five normal adult volunteers were included in the study. Three sets of randomized keratometry measurements were taken from both eyes of each adult, with both instruments by two independent observers. Readings included powers of the steep and flat meridians and axis of the flat meridian. The mean difference between the two instruments was calculated. The variance of each instrument was calculated for the axis, the steep and flat meridians, and the mean of the two meridians.

There was no significant difference between the mean Nidek and Zeiss keratometry readings for the steep (0.015 mm; P = .167) or flat (0.054 mm; P = .069) meridian or axis measurements (P = .172). On repeated measurements, the within-subject and within-group variabilities, calculated separately for each instrument, were significantly less for the Nidek automated keratometer than the Zeiss keratometer (P < .01) when measuring the steep and flat meridians. There was however, a significant increase in axis variability using the Nidek keratometer (range 20 degrees; P < .01).

The Nidek automated keratometer was accurate, reliable, and easy to use and compared favorably with the manual Zeiss keratometer when measuring corneal curvature. In the handheld mode, the Nidek is not suitable for axis measurements. It has the additional advantage of portability.