Reliable calculation
Using steep and flat meridians to improve refractive predictions
Roibeard O’hEineachain
Published: Tuesday, May 1, 2018
[caption id="attachment_11607" align="alignleft" width="1024"]
Jorge Calvo-Sanz MD[/caption]
A new bicylindric intraocular lens calculation method based on the cornea’s steep and flat meridians appears to predict refractive outcomes with greater accuracy than the Haigis formula in cataract patients with low corneal astigmatism, said Jorge A Calvo-Sanz OD, MSc, Institute of Visual Sciences, Hospital La Zarzuela, Madrid, Spain.
“Bicylindric method showed an improvement in the refractive management of cataract patients predicting refractive outcomes up to 8% more accurately than classical IOL calculation methods,” Dr Calvo-Sanz told the 22nd ESCRS Winter Meeting in Belgrade, Serbia.
He presented the findings of a study in which he compared the predictability of bicylindric IOL power calculations with that of the Haigis formula in 62 eyes of 62 patients with a mean age of 71.63 years (49 to 87 years).
Four weeks after surgery, the mean difference between the spherical equivalent predicted by the Haigis formula and that achieved was -0.117 D, whereas the mean difference between the spherical equivalent predicted by the bicylindric approach and that achieved was -0.054 D, he noted.
Furthermore, the percentage of patients who achieved predicted refraction by the Haigis and the bicylindric method was 76.70% and 84.30% respectively. Moreover, the linear correlation between bicylindric formula and achieved result was positive and statistically significant (p<0.001), but the correlation between Haigis prediction and the achieved outcome was also positive but not statistically significant.
None of the patients had undergone previous ocular surgery or had ocular pathology other than cataract. In addition, all had axial lengths greater than 21mm, and a flat keratometry axis between
0 and 90 degrees. Optical biometry was performed using the IOLMaster700 (Carl Zeiss Meditec). All patients underwent implantation of an acrylic monocular lens through a 2.8mm clear paralimbal corneal incision at 135 degrees.
Dr Calvo-Sanz noted that IOL lens power calculation for cataract surgery is generally performed using biometrical measurements such as mean keratometry and axial length, and several regression formulas to obtain IOL power to get emmetropia in spherical equivalent. The bicylindric method of IOL power calculation uses both keratometry readings, steep and flat, to improve the reliability and precision of the prediction of refractive outcomes, he explained.
“IOL power calculation according to the bicylindric method of intraocular lens power calculation is a simple and reliable way to predict the final refractive outcomes in patients with low corneal astigmatism,” he concluded.
Jorge A Calvo-Sanz: jacalvosanz@gmail.com
Jorge Calvo-Sanz MD[/caption]
A new bicylindric intraocular lens calculation method based on the cornea’s steep and flat meridians appears to predict refractive outcomes with greater accuracy than the Haigis formula in cataract patients with low corneal astigmatism, said Jorge A Calvo-Sanz OD, MSc, Institute of Visual Sciences, Hospital La Zarzuela, Madrid, Spain.
“Bicylindric method showed an improvement in the refractive management of cataract patients predicting refractive outcomes up to 8% more accurately than classical IOL calculation methods,” Dr Calvo-Sanz told the 22nd ESCRS Winter Meeting in Belgrade, Serbia.
He presented the findings of a study in which he compared the predictability of bicylindric IOL power calculations with that of the Haigis formula in 62 eyes of 62 patients with a mean age of 71.63 years (49 to 87 years).
Four weeks after surgery, the mean difference between the spherical equivalent predicted by the Haigis formula and that achieved was -0.117 D, whereas the mean difference between the spherical equivalent predicted by the bicylindric approach and that achieved was -0.054 D, he noted.
Furthermore, the percentage of patients who achieved predicted refraction by the Haigis and the bicylindric method was 76.70% and 84.30% respectively. Moreover, the linear correlation between bicylindric formula and achieved result was positive and statistically significant (p<0.001), but the correlation between Haigis prediction and the achieved outcome was also positive but not statistically significant.
None of the patients had undergone previous ocular surgery or had ocular pathology other than cataract. In addition, all had axial lengths greater than 21mm, and a flat keratometry axis between
0 and 90 degrees. Optical biometry was performed using the IOLMaster700 (Carl Zeiss Meditec). All patients underwent implantation of an acrylic monocular lens through a 2.8mm clear paralimbal corneal incision at 135 degrees.
Dr Calvo-Sanz noted that IOL lens power calculation for cataract surgery is generally performed using biometrical measurements such as mean keratometry and axial length, and several regression formulas to obtain IOL power to get emmetropia in spherical equivalent. The bicylindric method of IOL power calculation uses both keratometry readings, steep and flat, to improve the reliability and precision of the prediction of refractive outcomes, he explained.
“IOL power calculation according to the bicylindric method of intraocular lens power calculation is a simple and reliable way to predict the final refractive outcomes in patients with low corneal astigmatism,” he concluded.
Jorge A Calvo-Sanz: jacalvosanz@gmail.com
Tags: iol power calculations
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