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Purpose: To compare applanation biometry (A-Scan) and optical coherence biometry (AL-Scan) methods for IOL power calculation based on Axial Length and post operative refractive outcome. Methodology: Prospective and Interventional Randomized Comparative Study, Sample size of 400, studied under two sub groups, for Axial Length readings and IOL power calculation by A-Scan (Biomedix) and AL-Scan (Nidek). Keratometry readings are taken only by AL-Scan.Results: Mean ± St. dev. of A.L. measured by App. Biometry was low (22.79 ± 0.9 mm) than Opt. Coh. Biometry (23.16 ± 0.78 mm) to be significant (P= .0001). Mean ± St. dev. IOL power was higher (21.75 ± 2.1D) than App. Biometry (20.88 ± 1.59 D) to be significant (P= 0.0001). Mean ± St. dev. of refractive status for Myopia is higher -0.97 ± 0.53 by App. Biometry than Opt. Coh. Biometry -0.5 ± 0.19, to be significant (P= 0.0001) and Mean ± St.dev. for Hyperopia is higher 0.98 ± 0.59 by App. Biometry than Opt. Coh. Biometry 0.46 ± 0.18, to be significant (P= 0.0001). Bland–Altman plots showed perfect agreement between both methods regarding A.L. and calculated IOL power. Further subgroup analysis revealed a statistically significant difference in different age groups and types of cataract for Posterior Sub capsular cataract alone and Nuclear Sclerosis with Posterior Sub capsular cataract (P= 0.001). Conclusion: There is significant difference between App. and Opt. Coh. Biometry; however, certain situations of Cataract is demanding mandatory role of App. Biometry.