Abstract Background: Keratoconus is a progressive bilateral disease characterized by corneal thinning. Cross linking is one of the most effective treatments of keratoconus and here we studied its objective and subjective effects. Aim of Study: This study aims to investigate differences in objective and subjective outcome of collagen corneal crosslinking of different keratoconus grades. Patient and Method: Twenty-four eyes of twenty-four patients with keratoconus were enrolled in this prospective study arranged into 2 groups according to k reading (Group I: Less than 48, Group II: 48-52); 12 eyes of patients in each group all the eyes underwent full ophthalmological clinical evaluation (Best Spectacle Corrected Visual Acuity (BSCVA) by log MAR and wave light Pentacam assessment to investigate Keratometry readings, Central Corneal Thickness (CCT), and Aberrations scan by Zernike analysis. Evaluations were done at baseline and 3 months' post CXL. Results: The BCVA insignificantly deteriorated in group I & II after 3 months follow-up by (0.016±0.04) p=0.166 and (0.016±0.08) p=0.503 respectively. The mean average K insignificantly decreased in group I & II by (0.216±0.63) p=0.261 and (0.250±1.66) p=0.619 respectively. The mean central corneal thickness increased in group I by (11.00±31.97) p=0.258 while decreased in group II by (5.750±16.75) p=0.259. The mean of total aberration of group I decreased by (0.033±  0.09) p=0.219, while in group II increased by (0.666±0.49) p=0.503. Conclusion: We found insignificant decrease in (BCVA, Average K,) in the two groups the mean CCT increased in group I and decreased in group II. The mean of total aberration decreased in group I while increased in group II.