Comparison of Keratometric Values Measured by the Handheld Autokeratometer, On-table Autokeratometer and Manual Keratometer

PURPOSE: To compare the keratometry measurements by the handheld Nikon Retinomax K-plus2, the on-table Canon RK-5 autokeratometer, and the manual Topcon OM-4 keratometer and to evaluate the degree of agreement among the three instruments. METHODS: Adults (n=30) and children (n=40) presenting toa tertiary eye hospital clinic were examined by an optometrist. Topcon OM-4 keratometer, Nikon Retinomax and the on-table Canon RK-5 autokeratometer analyses were performed in order. The horizontal and vertical keratometry data were measured. The vector components of astigmatism, mean bias and agreement among the three types of measurements were evaluated. RESULTS: There were no significant differences among the three keratometers in horizontal or vertical keratometry or in central corneal astigmatism in both the adult and child groups (p-value>0.05). The keratometers which were estimated with Retinomax K-plus2 were highly correlated with those by on-table RK-5 autokeratometer (min. 0.89, max. 0.97) and Topcon OM-4 keratometer (min. 0.67, max. 0.94) in the adult group, while in the child group, the three instruments showed slightly decreased correlation (min. 0.45, max. 0.97 on RK-5, min. 0.36, max. 0.92 on OM-4), especially in the left eyes. CONCLUSIONS: The handheld Retinomax K-plus2 provided comparable data to that of the conventional on-table Topcon and manual keratometers. This instrument will beuseful in the clinic to measure keratometry in children or immobilized patients who have difficulty sitting during the examination.

Position-induced Cyclotorsion under Monocular Fixation

PURPOSE: To determine whether cyclotorsion occurs when a patient moves from the seating to supine position fixating with one eye. METHODS: The axis of astigmatism was measured with the handheld automated refractometer (Retinomax K-plus, Nikon, Japan) in 33 eyes having more than -1.0D cylinder in seated and supine positions under monocular fixation. RESULTS: There was a cyclotorsional deviation in 30 eyes (90.90%). Excyclotorsion was shown in 22 eyes (66.67%) and incyclotorsion in 8 (24.24%). Seventeen eyes (51.50%) had a torsional deviation less than 4 degrees, 5 eyes (15.15%) from 5 to 6 degrees, 7 eyes (21.21%) from 7 to 14 degrees and one eye greater than 15 degrees. CONCLUSIONS: Positionally induced cyclotorsion occurs under fixation with one eye simulating refractive surgery. Surgeons should therefore make an effort to align the wavefront measurement to the ablation onto the cornea.