Instant vision assessment device for measuring refraction in low vision

Clinical relevance: Refracting low vision patients require special procedures and strategies. A device-taking the reduced visual acuity and higher blur tolerance into account-is designed to measure refraction in this group.Background: Instant Vision Assessment Device (IVAD) is a stenopaeic slit refraction system in a binocular telescopic optometer calibrated to measure refraction. This study aims to validate IVAD in measuring refraction of low vision patients.Methods: Refractions were measured with IVAD on the right eyes of 35 normal subjects (ages nine to 69) and on the better eyes of 20 low vision subjects (ages 60 to 90) and compared with subjective refraction (SR). The visual acuities were compared in the low vision group. Paired Student t-test and Bland-Altman analysis were used to test the significance of difference and limits of agreement between methods, respectively.Results: In normal subjects, mean spherical equivalent refraction (M) measured by IVAD and SR was -2.88 ± 2.51 D and -2.72 ± 2.29 D, respectively, and the difference of -0.16 ± 0.47 D was not statistically significant (p = 0.05, t = 2.03). In low vision subjects, M measured by IVAD and SR was-0.66 ± 2.64 D and -0.55 ± 2.61 D, respectively, and the difference of -0.11 ± 0.59 D was also not statistically significant (p = 0.43, t = 2.09). Only the astigmatism J0 in the normal subject group of -0.03 ± 0.24 D by IVAD and 0.07 ± 0.17 D by SR showed a statistically significant difference of -0.10 ± 0.25 D (p = 0.04, t = 2.03). In low vision subjects, mean visual acuities with refraction from IVAD and SR were 0.52 ± 0.32 logMAR and 0.53 ± 0.32 logMAR, respectively, and the difference of 0.01 ± 0.07 logMAR was not statistically significant (p = 0.51, t = 2.09). At least 80% of the IVAD measure of refraction components (M, J0, J45) were within ±0.50 D of SR measure.Conclusion: IVAD is a practical and valid refraction method for low vision patients.