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Session Title: New evaluation tools in refractive surgery
Session Date/Time: Sunday 06/10/2013 | 08:00-09:30
Paper Time: 09:06
Venue: Forum (Ground Floor)
First Author: : V.Sicam THE NETHERLANDS
Co Author(s): : R. Ensing R. van der Heijde N. Reus
To investigate the performance of corneal topographers compared to a standard optical biometer in corneal astigmatism measurements.
The study was performed at the Rotterdam Ophthalmic Institute, Rotterdam, The Netherlands. the patients recruited were catarct surgery patients from the Rotterdam Eye Hospital, Rotterdam, The Netherlands.
Corneal measurements were gathered from 34 eyes of 30 pre cataract surgery patients. Keratron (Optikon, Rome, Italy): Placido Ring Pattern, Pentacam (Oculus, Wetzlar, Germany): Rotating Scheimpflug, Lenstar LS 900 (Haag-Streit, Koeniz, Switzerland): Monochromatic LED reflections and Cassini (i-Optics, The Hague, The Netherlands): Color LED reflections were used to determine keratometric indices of the anterior cornea: Ksteep, Kflat and axis of flattest meridian from which corneal astigmatism is derived. Three trials per eye were done to assess for precision and the trial with the median astigmatism was chosen for inter-instrument comparison.
The magnitude of astigmatism measured was 0.92 ± 0.56, 1.03 ± 0.52, 0.84 ± 0.60 and 0.75 ± 0.54 Diopters for Keratron, Pentacam, Lenstar and Cassini respectively. The axis of astigmatism measured was 141 ± 39, 152 ± 48, 154 ± 48 and 150 ± 53 for Keratron, Pentacam, Lenstar and Cassini respectively.The precision in the magnitude of astigmatism measured was 0.16 ± 0.15, 0.23 ± 0.12, 0.14 ± 0.13 and 0.11 ± 0.13 Diopters for Keratron, Pentacam, Lenstar and Cassini respectively. The precision in the axis of astigmatism measured was 9.2 ± 10.5, 13.0 ± 12.6, 5.3 ± 5.8 and 4.8 ± 4.6 Diopters for Keratron, Pentacam, Lenstar and Cassini respectively. There was no statistically significant difference between instruments in measured astigmatism and its axis. The precision of the axis of astigmatism measurement of the Keratron differs significantly (p = 0.0091) to that of the Lenstar. For the Pentacam precision both the astigmatism and its axis differ significantly (p = 0.0014 and p = 0.0008) to that of the Lenstar. The difference between Lenstar and Cassini precision is not significant.
There was no significant difference in astigmatism measurements between the four intruments used in this study. However, significant differences were found in the precision of astigmatism measurements. For both the magnitude and angle axis of astigmatism, Color LED Corneal Topography and the Lenstar produced the best repeatability. The sensitivity of corneal topography to the irregular features of the cornea may worsen repeatability of astigmatism measurements but it appears that this is not the case for Color LED corneal topography. This may be useful in the clinical practice involving astigmatism correction.
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