To compare refractive measurements, keratometry, pachymetry, and tonometry between two commercially available systems: Visionix VX650 (Luneau Technologies, France) and Nidek TonoRef III (Nidek, France).

This is a retrospective cohort study in which 415 valid eye measurements of 206 patients were obtained using both machines. Three groups were created: 1. The refraction group included 206 patients (400 eyes); 2. The keratometry group included 147 patients (293 eyes); 3. The pachymetry and tonometry group included 123 patients (245 eyes). To test agreement, each subject was measured once with each instrument.

In the first group, there was no statistically significant difference in sphere measurements (p = 0.072), but there was a significant difference in cylinder power (p = 0.014) and axis (p = 0.009) measurements. The second group had a strongly significant difference between keratometry power measurements (p = 2.784 × 10 ⁻⁵ ), but no statistically significant difference in mean keratometric axis measurements (p = 0.191). The third group found a strongly significant difference for pachymetry (p = 9.632 × 10 ^-10 ), but none for corrected tonometry (p = 0.064).

The two devices demonstrated variable levels of agreement depending on the parameter analyzed. Nevertheless, both machines have merit in measuring refraction and detecting glaucoma.

Good agreement between the two instruments was found for sphere power and corrected tonometry. Nevertheless, differences in refractive and keratometric axis measurements, as well as pachymetry, highlight the fact that the same instrument should be used for follow-up.