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Objective: The primary aim of this study was measure and compare the axial length (AXL), keratometric indices (K1, K2) and anterior chamber depth (ACD) by biometric devices; IOL Master and OB 820, to seek evidence on level of agreement for these parameters between these two devices. Study Design: Quasi-experimental study. Place and Duration of Study: Armed Forces Institute of Ophthalmology, Rawalpindi Pakistan, from Jul 2016 to Apr 2018. Methodology: This study was carried out at Armed Forced Institute of Ophthalmology on seventy eyes of 53 patients with senile grade II and grade III cataract. All patients underwent comprehensive ophthalmic and biometric examination using two different optical biometry devices the IOL-Master (Carl Zeiss Meditec, Jena, Germany) and OB-820 (Wave Light, Germany). Parameters of study were axial length (AXL), kera to metric indices (K1, K2) and anterior chamber depth (ACD). The results were evaluated using Bland-Altman analyses for level of agreement (LoA). The differences between both methodologies were assessed using the paired samples t test, and their correlation was evaluated by intra class correlation coefficient (ICC). Results: The mean age was 62.97 ± 7.97 years with the male/female ratio of 28/25. Mean axial length assessed by OB820 and IOL Master differed significantly in two groups, with a p-value of 0.018. Bland-Altman analysis further confirm significant difference range and 95% limits of agreement and ICC=0.659) of agreement for AXL. While, other parameters, K1, K2 and ACD showed an outstanding agreement (range within 95% confidence interval by Bland-Altman analysis) and internal consistency and reliability (ICC=0.960, 0.968. 0.976 respectively). Conclusion: The IOL-master and OB-820 should not be used interchangeably due to lack of agreement in axial length measurement the most important parameter for biometry. Both devices may provide consistent results regarding keratometry K1, K2 and ACD. [ABSTRACT FROM AUTHOR]