Comparative Evaluation of Accuracy of Immersion A-scan Ultrasound Biometry and Optical Biometry in Cases Undergoing Small Incision Cataract Surgery

Abstract

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.

Keywords

• auto-refractokeratometry
• axial length
• cataract
• intraocular lens
• phacoemulsification