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Comparison of optical coherence biometry and conventional ultrasound biometry in intraoculer lens power calculation

Poster Details

First Author: A.Yazici TURKEY

Co Author(s):    E. Söğütlü Sarı   M. Yüceur   G. Şahin   A. Kılıç   S. Ermiş  

Abstract Details



Purpose:

To compare the measurements of optical coherence biometry and ultrasonic biometry and evaluate the impact of experience in ultrasonic biometry.

Setting:

Fifty-four consecutive cataract patients were recruited to the study. Secondary cataracts due to trauma, chronic uveitis and previous intraocular surgery was excluded.

Methods:

IOLMaster (Carl - Zeiss IOLMaster 500) was used as the optical coherence biometry in the calculation of intraocular lens (IOL) power. The ultrasonic axial measurements and conventional keratometry was performed by a senior and junior registrar in order to evaluate effect of experience in conventional biometry calculation. Keratometry was done by Huvitz(HR 7000A) and ultrasonic axial measurements were done using Nidek(us-4000 ECHOSCAN). The formula used in both IOLMaster and conventional biometry was SRKII. Cataract surgery was performed using a 2,8 clear corneal incision with two side incisions. A foldable intraocular lens was used in all patients. Patients were evaluated postoperatively on day 1, week 1 and on the first month. Postoperatively refraction was measured at the end of first month using an autorefractometer. The spheric equivalents were recorded for statistical compairisons. Keratometric, axial length, calculated IOL power and postoperative refractive error were compared among IOLMaster, senior and junior registrar measurements and calculations. One way ANOVA and post-hoc tukey tests were performed.

Results:

Axial length measurements between the IOLMaster and the ultrasonic measurements of the junior and senior registrar were statisticaly significant (p<0.05, t test). However, there was no statistical difference between the measurements made by the junior and senior registrar (p>0.05). There was no significant difference between mean values of K1 and K2 (p>0.05). The calculated mean IOL power calculations for IOLMaster, senior and junior registrars were 22,0±1,5, 23,4±2,1 and 23,6±1,9 diopters respectively. The difference was significant between IOLmaster and registrars (p<0.05 and p<0.05) for senior and junior registrars respectively) but no statistical difference existed in comparison of senior and junior registrars (p>0.05). The mean postoperative refraction calculated by the IOLMaster was -0,48 ± 0,74 diopters. Whereas the predicted postoperative refraction for senior and junior registrars was -1,06±1,33 and -1,22±1,08 respectively.

Conclusions:

The intraocular lens selected according to the IOLMaster calculation, was found to be very successful in predicting postoperative refraction. Studies have shown the reason for an inaccurate postoperative refraction is due to faulty axial length measurements with an error of 100 micrometers leading to an error of 0,28 D in postoperative refraction. A lack of indentation of the eye, a higher chance of a measurement through the optic plane, lack of intra/interobserver variance are the reasons for the IOLMaster being superior to conventional ultrasonic biometry. With conventional measurements due to contact with the cornea the axial length measurement is calculated to be shorter then in reality and due to this there was a myopic shift in the predicted postoperative refraction. Another disadvantage in conventional ultrasonic biometry is the intra/interobserver variance of the measurements. There was no statistically significant difference in our study, however the standard deviation in the postoperative predicted refractive values between 1,33 and 1,08 show that intra/interobserver variation may exist. In conclusion, we recommend that due to its preoperative patient comfort as well as its success in limiting postoperative refractive error, IOL master should be preferred to the conventional methods. FINANCIAL INTEREST: NONE

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