We recently conducted a study to evaluate the consistency of measurements provided by the VX120 system.9,10 In this study, we evaluated a total of 107 healthy eyes of 107 patients with ages ranging from 23 to 65 years at the Optometric Clinic of the University of Alicante.
Inclusion criteria were: age of more than 18 years, refraction error between +5.00 and -10.00 D and eyes without pathology. Exclusion criteria were previous ocular surgery; glaucoma; fewer than 18 complete consecutive Placido rings projected on the cornea and therefore considered for the corneal analysis pseudophakia; corneal ectatic diseases; and any other type of pathologic condition of the eye.
A complete eye examination was performed in all cases, using the device to measure uncorrected visual acuity, and to obtain objective refraction, air tonometry and corneal topographic and anterior segment readings. In all cases, three consecutive measurements of objective refraction and ocular aberrations were obtained to assess intrasession consistency.
The within-subject standard deviation (Sw) and intrasubject precision (1.96xSw) for refractive data were below 0.12 D and 0.20 D in all cases, respectively. Concerning the aberrometric measurements, Sw and intrasubject precision values were below 0.05 µm and 0.10 µm, respectively. No statistically significant correlations of refractive measurements with their Sw associated were found (-0.033 ≤ r ≤0.053, P ≥ 0.064).9
Regarding topographic parameters of the anterior corneal surface, all Sw for curvature measurements were below 0.05 mm. The Sw for the magnitude of corneal astigmatism calculated for different areas of analysis was below 0.21 D.
Concerning the axis of corneal astigmatism, its Sw was below 11.27º. Corneal eccentricity showed Sw of 0.067. The analysis of the consistency of corneal aberrometric measurements showed a Sw of 0.048 µm for the root mean square associated to higher-order aberrations (HOA). For the aberrometric parameters of the third and fourth order, all Sw were below 0.037 µm.10
Concerning the anatomical measurements of the anterior segment, the results were excellent, with Sw within acceptable ranges. The Sw for anterior chamber depth (ACD) was 0.03 mm and remained below 9 µm for central and peripheral pachymetry.
For iridocorneal angle (IA) measurements, SW values of 0.84 or lower were found. The SW for white-to-white corneal diameter was 0.24 mm. No statistically significant correlations were found between any anatomical parameter evaluated and their associated Sw values (-0.220 ≤ r ≤ 0.204, P ≥ 0.125).