Comparative Study of Pre-Operative IOL Power Calculation by IOL Master, Immersion and Non Immersion Techniques (A Scan, Manual Keratometer)

Comparative study of pre-operative IOL power calculation by IOL master, immersion and non immersion techniques (a scan, manual keratometer) Dr. Hiral Solanki1, Dr. Dhara Patel2, Dr. Aishwarya Chhabra3 Gujarat University, M and J institute of ophthalmology, 6 Nirmala Appt, Maninagar, Ahmedabad, India Hiral. solanki@gmail. com Gujarat University, M and J institute of ophthalmology, 11/ganesh park-2, opp. vishvas city-2, RC technical road, ghatlodia, Ahmedabad, India. dhara_patel08@yahoo. com Gujarat University, M and J institute of ophthalmology, 11, bajaj nagar enclave, opposite gandhinagar railway station, Jaipur, India. aishwaryachhabra@gmail. com Cataract removal and artificial intraocular lens implantation is one of the most frequent and successful ophthalmic surgical procedures today. One of the remaining problems, however, is the accurate calculation of intraocular lens power necessary for attaining the desired postoperative refraction. Refractive outcome following phacoemulsification depends upon accuracy in multiple variables used in biometry technique. In this study I have compared the intraocular lens power calculation by conventional applanation ultrasound, conventional immersion ultrasound and partial coherence laser interferometry. intraocular lens power calculation, IOL Master, keratometry, immersion technique and contact technique of axial length measurement. A-scan.1. Introduction Cataract removal and artificial intraocular lens implantation is one of the most frequent and successful ophthalmic surgical procedures today. One of the remaining problems, however, is the accurate calculation of intraocular lens power necessary for attaining the desired postoperative refraction. Refractive outcome following phacoemulsification depends upon accuracy in multiple variables used in biometry technique. Individual contribution is as follows Variable in biometry its attributable error in % in predicting post operative refraction following cataract surgery Keratometry 54 % AC depth 8 % IOL power formula 38 % Quality of an IOL Variable Preoperative biometry of intraocular distances, especially the axial eye length, is the most critical step for an accurate calculation of the intraocular lens refractive power. A-scan ultrasonography is routinely used in ophthalmologic biometry. Recently a new technology has been included in a machine called IOL master which is claimed to be comparable to the time tested Ultrasound biometry. But as always a new technology has to undergo multiple tests before it can take a place of gold standard test. There are many studies done and being done worldwide over the predictability of IOL Master (in comparison to the ultrasound biometry) for post operative refraction in cataract surgery. Mixed responses have been seen so far. The clinical accuracy of the axial eye length measurement using conventional ultrasound biometry has been reported to be approximately 100 to 120 mm. An axial eye length measurement error of 100 mm would result in a corresponding postoperative refractive error of 0.28 diopter.2. Aims and objectives The purpose of the study was to compare 3 different methods of IOL power calculations [ i. e. (1) conventional applanation ultrasound (2) conventional immersion ultrasound (3) partial coherence laser interferometry. ] for the accuracy of intra ocular lens (IOL) power calculation and thereby to evaluate the predictability of each technique in terms of refractive outcome of patients undergoing cataract surgery.3. Materials and Methods In this Prospective Randomized clinical trial, 75 patients undergoing phacoemulsification cataract surgery by same surgeon were randomized to undergo biometry with either A-scan applanation ultrasound, A-scan immersion ultrasound or partial coherence laser interferometry (optical biometry). Patients were divided in three groups. Each group consisting of 25 patients.1st group of patients (n=25) underwent IOL power calculation by A-scan applanation ultrasound.2nd group of patients (n=25) underwent IOL power calculation by A-scan immersion ultrasound.3rd group of patients (n=25) underwent IOL power calculation by IOL master. Confounding factor between two groups is axial length which is between 21-25 mm. PATIENT EXCLUSION CRITERIA - 80 years of age - Mature cataracts, dense cataracts - ANY MACULAR PATHOLOGY - Retinal Detachment, Vitreous hemorrhages - Corneal scars, tear film abnormalities - Mentally challenged patients or - patients with ocular Motility disorder - AL more than 25 and less than 21 mm - Prior history of refractive surgery in same eye. The applanation A-scan, BIOMEDIX Echo RULE-2 was used for ultrasound biometry and the IOL MASTER ( Zeiss Humprey Sys