Validity and precision of a novel instrument that combines wavefront aberrometry, autofraction and corneal topography with a stationary Scheimpflug camera.

Abstract

Purpose : To evaluate the validity and precision of a novel instrument, the VX120 (Visionix Luneau, Chartres, France), that combines wavefront based autorefraction with stationary Scheimpflug imaging of the anterior chamber.

Methods : In this prospective study, subjects were recruited from healthy first year students at Hadassah Academic College, ages 18-38. Subjects were measured 3 times with the Sirius rotating Scheimpflug camera (CSO, Italy) and the VX120, by different technicians. Subjective refraction was carried out by one qualified optometrist. The optometrist and technicians were masked to one another's results and exams were performed in a random order. A subset of subjects was tested one week later for repeatability evaluation. Bland and Altmann analysis was used to assess agreement and precision. Only the right eye was included for analyses.

Results : 61 subjects (42 women) participated in the refraction validation study (24.36±7.29 years old). The mean difference between subjective refraction and the VX120 autorefraction for sphere, spherical equivalent (SE) and astigmatic vectors J₀ and J₄₅ was, 0.14±0.47D, 0.01±0.34D, 0.10±0.18D and 0.047±0.17D, respectively. Repeatability was assessed on 37 patients. Intra-test repeatability showed small within-subjects standard deviation (Sw=0.38 to 0.39) and inter-test repeatability showed no statistically significant difference between the first and the second session for all parameters (p>0.33).
71 subjects (49 women) participated in the Scheimpflug imaging validation study (24.30±6.61 years old). The difference between the VX120 and Sirius for central corneal thickness (CCT), iridocorneal angle and anterior chamber depth (AD) were 26.12±11.46µm (-3.51±11.46µm with calibration offset), 0.93 ± 3.83° and -0.005 ± 0.118mm, respectively.
Repeatability was assessed on 35 subjects. Intra-test repeatability showed small Sw of 2.85, 1.08 and 0.21 for CCT and iridocorneal angle and AD, respectively. Inter-test repeatability showed no statistically significant difference for any of the anterior chamber parameters measured by the VX120 (p>0.25).

Conclusions : The VX120 shows good agreement and repeatability values.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.