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Posterior corneal astigmatism contribution to residual astigmatism following cataract surgery
Session Title: Assessment of Astigmatism
Session Date/Time: Saturday 05/10/2013 | 11:00-12:30
Paper Time: 11:24
Venue: Main Lecture Hall (Ground Floor)
First Author: : Y.Ton ISRAEL
Co Author(s): : A. Abulafia O. Reitblat A. Levy E. Assia
To compare the residual astigmatic error following cataract surgery and toric intra-ocular lens (IOL) implantation using either anterior corneal keratometry, anterior and posterior corneal astigmatism measurements or anterior corneal measurements with adjustment according to the Baylor Toric IOL Nomogram.
Ein-Tal Ophthalmology Center, Tel Aviv, Israel
Corneal astigmatism was measured pre-operatively and post-operatively in consecutive cataract cases with a toric IOL implantation, using an optical biometer (Lenstar LS 9oo) and Scheimpflug Camera (Pentacam). Post operative residual astigmatic error vector analysis, including IOL toricity and location and surgically induced incisional astigmatism, was used to compare 3 different methods of corneal astigmatism measurements: (1) Optical biomentry (2) Anterior corneal astigmatism using the Lenstar and vector subtraction of the posterior corneal astigmatism measured by the Pentacam, and (3) True net corneal power as given by the Pentacam device.
The above calculations were repeated, substituting the implanted IOLs with the IOL toricity recommended by the Baylor Toric IOL Nomogram.
Residual astigmatism using optical biometry, anterior optical biometry with posterior tomographic measurements and true net power of the cornea, was determined to be 0.71D at 158°, 0.66D at 132° and 0.96D at 139°, respectively. In 50% of cases IOL toricity adjustment according to the Baylor Nomogram was required. Following the adjustment, simulated residual astigmatism with each method was 0.69D at 152°, 0.7D at 131° and 1.0D at 138°, respectively.
Posterior corneal astigmatism was found to reduce residual corneal astigmatism following cataract surgery with toric IOL implantation. Furthermore, post-operative astigmatic error meridian has shifted from against-the-rule dominance towards the vertical orientation. Incorporating either measured or estimated posterior corneal astigmatism in the calculation of IOL toricity amount and axis improves refractive astigmatic outcome.