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Introduction: The evolution of modern technologies for cataract surgery has made it crucial for aiming emmetropia with highly defined vision. The key factor responsible for postoperative emmetropia is an accurate biometry, along with various other factors. Ultrasonic biometry is the gold standard method of Intraocular Lens (IOL) power calculation but the corneal indentation with the probe underestimate the axial length and result in a myopic shift which is overcome by the newer optical biometry devices, including swept source optical coherence biometry which uses infrared light to measure the ocular distances. Aim: To determine the precision and accuracy of IOL power calculation by ultrasound A-scan and optical IOL master and their refractive outcomes. Materials and Methods: This prospective, and observational study was conducted between September 2019 to February 2021 in 155 patients with cataract undergoing phacoemulsification in Kalinga Institute of Medical Sciences, KIIT University, Bhubaneswar, Odisha, India. All subjects underwent comprehensive ocular examination and biometry with two formulae {Sanders-Retzlaff-Kraff (SRK) and Holladay-I}. Biometry included corneal curvature (keratometry), axial length, anterior chamber depth, IOL power calculation, predicted refractive error. There were two broad groups. One group underwent biometry by ultrasound A-scan and the other group underwent optical biometry by IOL Master 700. The IOL power was calculated with the two formulae in both the groups. Comparisons between variables measured using the IOL master and A-scan were done using paired t-test. The p-values <0.05 were considered statistically significant. results: In a 18 month period, 155 eyes were consecutively enrolled in the study. The mean age of all enrolled patients was 62.1±8.65 years (range 34-80 years) with male:female ratio of approximately 1.25:1. The mean axial length measured by IOL master was higher (23.15 ± 0.85) than that by A-scan (22.96±0.81 diopters) with a mean difference of 0.197±0.35 mm (p-value <0.001, paired t-test). The mean predicted IOL power was 20.81±1.84 diopters by IOL master and 21.13±1.62 by A-scan by SRK-II formula (p-value <0.001). While mean predicted IOL power with Holladay-I by IOL Master 700 was 20.61±1.92 and 21.44±1.98 diopters by A-scan with a mean difference (-0.82±0.76 diopters) with a significant p-value <0.001. Bland-Altman analysis plots showed almost perfect agreement between both methods regarding predicted IOL power. conclusion: The swept source Optical Coherence Tomography (OCT) based IOL master 700 proved to be a faster non contact device to use with a shorter learning curve, higher accuracy in average axial length eye and less refractive surprises. [ABSTRACT FROM AUTHOR]

Introduction: At present, refractive accuracy is the demand of cataract surgery which can be achieved by providing precise post-operative vision without spectacles. One of the important factors required to give spectacle free vision is calculation of accurate biometry. In developing countries like India, Small Incision Cataract Surgery (SICS) is done more commonly than phacoemulsification with foldable Intraocular Lenses (IOLs). Aim: To evaluate the accuracy of Immersion A-scan and Optical biometry in patients undergoing SICS with foldable IOLs by assessing their one month post-operative refraction and converting these values in predicted emmetropic IOL powers. Materials and Methods: Prospective study was conducted on 60 patients to be posted for cataract extraction in Department of Ophthalmology, Bharati Medical College and Hospital (Deemed to be university), Sangli, Maharashtra, India, for two months from the period of January 1, 2019 to March 1, 2019. Preoperatively patients were randomly divided in two groups containing 30 patients each, Group A was subjected to Immersion A-scan and Group B to Optical biometry. Patients included in the study preoperatively also underwent Best Corrected Visual Acuity (BCVA) estimation, applanation tonometry, slit lamp examination of anterior and posterior segment and Keratometry. Patients were examined post-operatively on 1st, 7th, and 30th day, for slit lamp examination of anterior and posterior segments and also their BCVA was noted. Final refraction was given on 30th postoperative day based on their auto-refractometer readings. Postoperative refraction and actual IOL power placed was used to calculate IOL power that would have produced emmetropia in that particular patient by the help of regression formula. Difference in actual IOL power placed and predicted emmetropic IOL power was also noted in each patient of both groups. Unpaired t-test was used for the statistical analysis. Results: The mean Axial Length (AXL) measured by immersion A-scan in group A was lesser (22.91 mm) than that with IOL master (23.15 mm) with a mean difference of 0.24 mm (p=0.133). Mean actual post-operative refraction at one month in group A was higher (0.90) than that of group B (0.70) with a mean difference of 0.20 (p=0.166). Mean difference between actual IOL (aIOL) placed and predicted emmetropic IOL (eIOL) was higher in group A (1.35) than that of group B (0.96) with a mean difference of both group was 0.39 (p=0.021). Conclusion: In the range of AXL 22 mm to 24.50 mm, used in this study, there is no statistically significant difference in axial length measurements between two methods of Ultrasound biometry and Optical biometry. Patients in Group A of present study had significant post-operative residual refraction as compared to Group B patients, which can be attributed to inaccurate Keratometry as two different methods of Keratometry were done in two groups. Keratometry values can influence post-operative refraction and inaccurate Keratometry may land with post-operative refractive errors. Current study showed certain advantages of optical biometry over USG biometry in that Optical biometry is Non-contact, fast and accurate, but optical biometry cannot be done in mature cataracts and dense posterior subcapsular cataract where immersion USG biometry is required. [ABSTRACT FROM AUTHOR]