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Session Title: Intraoperative Biometry and Correction of Astigmatism
Session Date/Time: Monday 07/10/2013 | 08:00-10:00
Paper Time: 08:58
Venue: Main Lecture Hall (Ground Floor)
First Author: : N.Shroff INDIA
Co Author(s): : R. Dutta A. Koul G. Singh
To compare two different methods of analysis of pre-operative reference marking for Toric IOL after marking with an electronic two step reference marker.
Cataract & Intraocular Lens Implantation Service, Shroff Eye Centre, New Delhi, India.
44 eyes of 22 patients planned for Toric IOL implantation were included. All patients had pre-operative marking of both eyes done with an electronic pre-operative Toric IOL reference marker (ASICO AE-2929 Two Step Reference). All the markings were done by a single investigator with the patient sitting in an upright position fixating on a distant object. Reference marks were placed at 3- and 9-o"clock positions on the limbus with the pre-inked electronic marker. The marks were analysed with two systems with the patient seated in an upright position. Firstly, slit-lamp digital photographs taken by a single masked observer and analyzed using tools in Adobe Photoshop (version 7.0) by aligning a line through the nasal and temporal marks. Secondly, Tracey iTrace Visual Function Analyser (version 5.1.1) was used for capturing a corneal topograph exam and the position of the marks was read out from the grid at the limbus. The amount of alignment error (in degrees) from the horizontal, as well as any inter eye difference within the same group by both methods was calculated.
The Photoshop method showed a mean rotation of the reference marks of 0.52 ± 2.94 degrees clockwise from the horizontal axis, and the iTrace method showed a mean rotation of 0.59 ± 3.49 degrees anti-clockwise; the difference was significant (p =0.010). The mean absolute rotation error was 2.38 ± 1.78° by the Photoshop Group and 2.87 ± 2.03° in the iTrace method which was not statistically significant (p = 0.215). 72.7% eyes by the Photoshop method and 61.4% by the iTrace method had rotation error ? 3 degrees (p = 0.359); and 90.9% eyes by the Photoshop method and 81.8% by the iTrace method had rotation error ? 5 degrees (p = 0.344). While analyzing the inter eye difference, there was no significant difference in the absolute amount of rotation in degrees between the eyes when analyzed by either method.
A new method of pre-operative marking was evaluated. Both the analysis methods showed an approximately 3 degrees of alignment error, which could contribute to a 10% loss of astigmatic correction of a Toric IOL. We found that the alignment error with the electronic marker was not less than other markers (Bubble & Pendulum Marker). The iTrace provided a quick estimate of the alignment error of the reference marks. If the amount of error in pre-op marking is known for a particular eye one can adjust for it while performing the intra-operative marking to optimize the outcome.
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