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First Author: N.Shroff INDIA
Co Author(s): R. Dutta A. Koul J. Farooqui
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To compare two different methods of determining the post-operative position of the Toric IOL and to calculate the alignment error with each method
Cataract & Intraocular Lens Implantation Service, Shroff Eye Centre, New Delhi, India.
89 eyes of 61 patients with cataract and coexisting corneal astigmatism ranging from 1 to 4 diopters planned for Toric IOL implantation were included. All eyes underwent pre-operative automated keratometry and biometry. Toric IOL cylindrical power, axis of implantation and anticipated residual astigmatism was calculated using the web based Acrysof Toric calculator. All eyes underwent pre-operative reference marking to denote the 0Ḟ and the 180Ḟ positions (using bubble marker) followed by digital slit-lamp photography. All eyes were operated by the same surgeon, at the same incision location. At 3 months, the achieved IOL alignment was analyzed by aligning the slit-beam of the slit-lamp with the pair of marks denoting the axis of the IOL after pupillary dilation. Additionally, the IOL position was determined after capturing a digital retro-illuminated slit-lamp photograph, which was superimposed on the pre-operative photograph using single prominent major episcleral vessel around the limbus as landmark. The axis of orientation of the Toric IOL was determined using tools in Adobe Photoshop (version 7.0) by aligning a line through the marks denoting the IOL axis. The amount of alignment error (in degrees) by both methods induced with respect to the desired axis of alignment was calculated and statistically analyzed.
The mean pre-operative keratometry was 44.19 ±1.51 D, and the mean corneal cylinder was 2.54 ±0.90 D. The mean postoperative absolute cylinder was 0.57 ±0.28D. Toric IOL models used were T3(1.03 D): 28 eyes (31.5%), T4(1.55 D): 21 eyes (23.6%), T5(2.06 D): 18 eyes (20.2%), T6(2.57 D): 11 eyes (12.4%), T7(3.08 D): 4 eyes (4.5%), T8(3.60 D): 4 eyes (4.5%) and T9(4.11 D): 3 eyes (3.4%). Mean postoperative alignment error was 3.44 ±2.60D by the slit lamp method, and 3.89 ±2.86D by the Photoshop method with no significant difference seen between the two methods (p=0.384). 56 eyes (62.9%) by the Slit-lamp method and 52 eyes (58.4%) by the Photoshop method had rotation error ? 5 degrees (p = 0.526); and 78 eyes (87.6%) by the Slit-lamp method and 75 eyes (84.3%) by the Photoshop method had rotation error ? 10 degrees (p = 0.422).
Both Adobe Photoshop method and slitlamp observation were reliable and predictable methods of assessing IOL alignment. Although the sensitivity is more with the Photoshop method, the slit-lamp method is more accessible in an outpatient setup. The clinical outcome following Toric IOL implantation can be refined by reducing the alignment error which is dependent on an accurate keratometry and biometry, surgeon specific SIA, reference and intraoperative marking and finally placement of IOL in the bag.