PURPOSE: To assess the influence of reliability (repeatability and reproducibility) of eye parameter measurements on the prediction refraction by using the outcomes of nine optical biometers reported in the literature. METHODS: A search was conducted in PubMed focused on the outcomes from original studies regarding reliability. The mean population of within-subject standard deviation (Sw) was estimated from the mean samples reported in the included studies. Repeatability coefficients ( R ) for the mean population were computed as 2.77 × Sw. The influence of reliability on the prediction refraction for eye biometric parameters, such as mean corneal power in diopters (D) (Km), anterior chamber depth (ACD), and axial length (AXL), were evaluated using a thick lens formula. The lens thickness (LT), central corneal thickness (CCT), and white-to-white (WTW) distance were also evaluated. RESULTS: The repeatability of optical biometers ranged from 0.19 to 0.42 D for Km, from 0.04 to 0.13 mm for ACD, from 0.03 to 0.22 mm for AXL, from 0.06 to 0.13 mm for LT, from 5.5 to 17.7 µm for CCT, and from 0.18 to 0.48 mm for WTW distance. Total prediction refraction due to repeatability ranged from 0.21 to 0.61 D, with Km the variable that caused the major part of total prediction refraction variability, followed by AXL and ACD. Reproducibility for the evaluated variables was generally inside the repeatability ranges. CONCLUSIONS: New optical biometers are equally reliable as earlier technologies. Special attention should be focused on Km and AXL, which explain the major part of prediction refraction variability. [ J Refract Surg . 2022;38(2):120–127.]