PURPOSE: To evaluate the effectiveness and agreement of 3 optical biometers in measuring axial length (AL) and biometric parameters in the eyes of patients with mature cataracts. SETTING: Oftalmosalud Instituto de Ojos, Peru. DESIGN: Prospective, comparative study. METHODS: Eyes with mature cataracts were examined. Three consecutive scans were performed with each device: the IOLMaster 700, the Galilei G6, and the Pentacam AXL. The following parameters were recorded: AL, anterior flat keratometry (K1), steep K (K2), anterior astigmatism, mean K (Km), anterior chamber depth (ACD), central corneal thickness (CCT), and lens thickness. Agreement between devices was assessed using the coefficient of correlation of concordance (CCC). RESULTS: Forty-five eyes were included. After 3 attempts, the acquisition success rates in measuring mature cataracts were 84.4% (38/45), 42.2% (19/45), and 37.7% (17/45) for the IOLMaster, the Galilei, and the Pentacam, respectively. Significant differences were found between the Pentacam and the IOLMaster in terms of AL, K2, and CCT. Significant differences were found in terms of K1, K2, Km, ACD, and CCT between the Pentacam and the Galilei; and significant differences were found in AL, K1, Km, and ACD between the Galilei and the IOLMaster (P < .05 all). Good correlations were found between devices (>0.90) in terms of keratometries and AL. CONCLUSIONS: The IOLMaster 700 had the highest AL acquisition success rate when compared with the Pentacam AXL and Galilei G6. Good agreement between devices was found in terms of AL and K readings.