The preoperative corneal marking is an initial and crucial procedure for the accurate alignment of toric IOLs. For toric IOLs, every deviation of 3° from the intended meridian results in an astigmatic undercorrection of approximately 10%.
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The alignment axis of the toric IOL was obtained with the Calculation Tool software (version 3.2.4) provided on the Alcon website ( ).Įrrors in alignment can occur at several stages in cataract surgery and toric IOL implantation, including preoperative corneal biometry measurement, preoperative referent limbal marking, alignment on the intended meridian of toric IOL, and postoperative IOL rotation. An AcrySof® Toric IOL (Alcon Laboratories, Inc., Fort Worth, TX, USA) was implanted. The surgeries were performed by a single surgeon (HZ) as a routine procedure. The patients with previous intraocular surgery, corneal opacities, irregular astigmatism, glaucoma, macular disease, or diabetic retinopathy were excluded. Keratometry was performed using the iTrace aberrometer during corneal limbal marking. The axis length was measured with IOLMaster 500 (Carl Zeiss Meditec). The visual acuity was converted to the logarithm of the minimum angle of resolution. Uncorrected distance visual acuity (UDVA) and best-corrected visual acuity (BCVA) were recorded before and after surgery. The study complied with the principles laid down in the Declaration of Helsinki and was approved by the Ethics Committee of Guangdong Provincial People's Hospital. Written informed consent was obtained from the patients. Randomization was performed using computerized random number tables. Houston, TX).Īll patients were randomly divided into the TRP marking group (15 eyes) and slit-lamp horizontal meridian (SHM) marking group (15 eyes). The aim of this study was to introduce the three-random-point (TRP) marking method performed using the iTrace system (Tracey Technologies Corp.
However, using a digital image-guidance system has disadvantages of high cost and need for special equipment.
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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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