However, using a digital image-guidance system has disadvantages of high cost and need for special equipment. A digital image-guidance system used during toric IOL surgery is more reliable and precise than manual marking. Accurate preoperative marking of the eye with the patient in the sitting position can minimize the intraoperative misalignment errors. All manual methods for corneal marking can cause errors. Manual methods for horizontal meridian limbal marking were commonly used preoperatively, including the slit-lamp marking, surgeon's direct visual marking, bubble marker-assisted method, pendular marker-assisted method, and tonometer marking. The average cyclotorsion of the eye when the patient is changed from the upright position to the supine position is approximately 2°–4° but can be up to 15°. When the patient is changed from the standing or sitting position to the supine position, cyclotorsion of the eye can cause misalignment. Precise preoperative limbal marking is crucial for an accurate alignment of toric IOLs. Toric intraocular lens (IOL) implantation during cataract surgery was more widely used owing to its reliability and effectiveness. Several surgical techniques, such as limbal relaxing incisions, peripheral corneal relaxing incisions, and excimer laser surgery, are used to eliminate or decrease coexisting astigmatism in patients with cataract. Because persisting astigmatism can decrease the visual acuity and the vision quality of patients after cataract surgery, predictable correction of the preexisting corneal astigmatism is critical and popular. It has been estimated that 30% of patients with cataract have preexisting astigmatism of over 0.75 D 8% of the eyes have corneal astigmatism of over 2.00 D and 2.6% of the eyes have corneal astigmatism of over 3.00 D.
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