The goal of this study is to assess the effect of pupillary dilation on predicted post-operative  refraction  (the Plano or least minus refraction) and on recommended intraocular lens (IOL) power calculated by using the third generation and fourth generation formula to measure the difference  between pre  and   post   pupil  dilation  on ACD. This   study included 40 eyes with cataract will undergo phacoemulsification and divided into two   group  Group (A): 20 cataract patients with biometry by third formula (SRK/T and Hoffer Q).  Group (B):  other 20 cataract patients with biometry by fourth formula (Holladay 2). There were statically non-significant differences found between PPR before and after  pupil dilation in    Group A and  Group B with p value 0.861and 0.181 respectively. The main age of our patient in group A ranged from (21 – 42) years and age ranged from (25 to 45) in group B with statically   non-significant differences between two groups.