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Calculation of corneal astigmatism axis for accurate installation of Toric intraocular lenses with five different techniques

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Session Details

Session Title: Cataract II
Session Date/Time: Saturday 27/02/2016 | 08:30-11:00
Paper Time: 10:36
Venue: Trianti Room
First Author: : D.Eleftheriadou GREECE
Co Author(s): :    L. Mavroudis              

Abstract Details


Correction of astigmatism during cataract surgery with toric IOLs requires accurate preoperative determination of the positioning axis and precise intraoperative IOL alignment. With the advent of intraoperative image guided systems allowing precise IOL alignment, preoperative axis determination has become the most critical factor affecting the final outcome.


Ophthalmic Day Care Microsurgery Clinic Leonidas Mavroudis, Thessaloniki, Greece


Comparison of the preoperative corneal astigmatism axis measured with five different techniques. The refractometry-topography - keratometry Topcon KR7000P, IOL Master optical biometry, Biograph (Lenstar) optical biometry, iTrace Visual Function Analyser with the Osher marking system and the Verizon Image Guided System were used to measure corneal astigmatism axis in twelve eyes of nine patients. Measurements were performed preoperatively after slit lamp marking of the horizontal axis by experienced operators. Image analysis was also used for the Itrace, the Biograph and the Verion systems to avoid calculation errors due to incorrect head placement.


Statistically significant difference of the astigmatism axis was not observed between techniques (ANOVA p<0,05). When clinically signifficant difference was sought, significant difference was observed between the measurements of the Verion system and the mean of the five measurements. Moreover six of the twelve eyes measured with the Verion system had more than five degrees difference from the average of measurements. Significance was not reached for any of the other systems and difference of more than 5 degrees was found in one measurement of the Topcon and Biograph systems and in two measurements of the Itrace and IOL Master systems.


Although statistically significant diference was not observed when the means of the measuremet systems where compared, probably due to the small number of measurements, clinically signifficant errors may result if only one technique is used for the determination of the toric IOL positioning axis. The finding that a more than five degrees difference in the astigmatism axis was measured in a number of eyes with all systems leads to the recommendation that more than one measurement method should be used for the correct axis determination when Toric IOLs are implanted.

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