Thesis (M.Sc.) - Cairo University - Faculty of Medicine - Department of Ophthalmology

Background: Accurate measurement of total corneal astigmatism is critical in correcting astigmatism following cataract surgery and in accurate calculation of toric Iols .The astigmatism of the anterior and posterior corneal surfaces both contribute to the total corneal astigmatism. Previously, the posterior corneal astigmatism was neglected during measurement of total corneal astigmatism which resulted in errors during calculation and correction of astigmatism. Purpose: To determine the percentage of contribution of the magnitude of posterior corneal astigmatism to total corneal astigmatism using Pentacam (Scheimpflug) imaging . Method: This is a prospective cross sectional study conducted on 356 eyes of 356 patients, where the total corneal astigmatism was calculated by addition of anterior and posterior corneal astigmatism using vector analysis and then the percentage of posterior to total corneal astigmatism was calculated . Results: The percentage of contribution of posterior to total corneal astigmatism was about 30 % in patients 2 With the rule 3astigmatism and about 8% in patients 2Against the rule 3 astigmatism.Conclusion: posterior corneal astigmatism shouldn{u2019}t be neglected during calculation of total corneal astigmatism as neglecting posterior corneal astigmatism can result in errors during calculation and correction of astigmatism

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