Comparison Between the Instant Vision Assessment Device (IVAD) and the Focometer in Determining Refractive Error

Background: Uncorrected refractive error is a common cause of preventable blindness. In developing countries, eye care professionals and refraction tools are in scarce supply to meet the great demand for correcting refractive error.
This study aims to compare the Focometer and the Instant Vision Assessment Device (IVAD) in obtaining subjective refractions.

Methods: Self-refractions were performed with the Focometer and the IVAD, respectively, on the right eye of 27 subjects. The range of age was from 23
to 51 years, and the mean age was 37.4±7.8 years. Subjects were in a rehabilitation center in Osaka, Japan. The spherical equivalent refraction findings
obtained with both instruments were compared. Paired t-test, regression analysis, and Bland-Altman plot were used for statistical analysis.

Results: The mean spherical equivalent refraction and the standard error measured by the IVAD in the right eye was -2.00±0.46 D. With the Focometer, these were -1.89±0.47 D. The difference in the measurement and the standard error between the IVAD and the Focometer was -0.12±0.16 D, which
was not statistically significant (p = 0.46, t = 0.75). The results obtained by the 2 instruments were highly correlated (R2 = 0.89; p = 0.00), and there was no systemic measurement difference between the two instruments.

Conclusions: Refractive error findings obtained with the Focometer and the IVAD are comparable to each other. Both instruments are valid and useful tools for determining spherical equivalent refractive error.