الفهرس 
The Aim of The WorkOnly 14 pages are availabe for public view
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Abstract
Summary
Cataract is the leading cause of preventable blindness worldwide. Cataract extraction surgery and implantation of intraocular lens (IOL) is the most frequently performed ophthalmic surgical procedure worldwide. That makes accurate calculation of the IOL power to attain the best postoperative refraction a research issue.
A lot of factors has an affect on the refractive outcome after cataract extraction surgery, including axial length, keratometry, and lens formulas. The preoperative axial length measurement is a key determinant in the choice of intra-ocular lens power.
This study was aiming to compare between optical biometry and ultrasound biometry regarding the accuracy of Intra-Ocular Lens Power calculations for cataract surgery as measured by postoperative refraction improvement in Emmetropic eyes and High myopic eyes.
Traditionally, contact A-scan ultrasonography is used. This measures the time taken for sound to traverse the eye and converts it to a linear value (spikes) using a velocity formula. The distance between the corneal and retinal spikes gives the axial length of the eye. keratometry reading (K1&K2) taken by manual keratometer.
The Optic Biometry (IOL-master 700) device is a computerized biometry device consisting of an OCT system to measure distances within the human eye along the visual axis, a keratometer system to measure the corneal surface.
60 eyes from patients scheduled for phacoemulsification were included in the study. A scan biometry was done to 30 of them where 15 eyes were highly myopic and 15 eye were emmetropic. IOL master biometry was done to the other 30 eyes where 15 of eyes were highly myopic and 15 eyes were emmetropic.
Results show that the axial length measured using the IOL master was 0.25mm longer than that measured using A- scan which was statically insignificant (p=0.741).
In the emmetropic group, the mean difference between the two methods was 0.9 mm, which was statically significant (0.002). In the high myopic group, we found that the mean difference between the two methods was 0.41 mm, which was statically insignificant (p=0.544).
The difference between the mean absolute errors (MAE) measured by IOLM and the mean absolute errors (MAE) measured by A scan was 0.25 (P=0.019) which was statistically significant improving a 0.44 D error (MAE measured by A-scan) to 0.19 D error (MAE measured by IOLmaster).
We can observe that the optical biometry (IOL master) provides more accurate axial length measurement and thus results in more accurate calculations of intraocular lens power. Despite the fact that, IOL master shows a failure rate in the presence of dense cataracts.