Axial-length computation using corneal dimensions and A-scan biometry

Abstract

Objective: To compare the axial length derived from a formula incorporating corneal dimensions with the results obtained by A-scan biometry. Methods: This is a nonrandomized comparative study of patients from the outpatient department of a tertiary-care academic medical institution who were screened for cataract surgery. Corneal diameter and slope were measured with a Vernier no. 6 caliper and axial length determined using Ophthasonic A-Scan III machine. Computed axial lengths were arrived at using a formula incorporating corneal diameter and slope. The mean difference of measured and computed axial lengths were statistically analyzed using paired t test and general linear model tests. Results: A total of 105 eyes (96 patients) were included in the study. The mean difference between computed and measured axial lengths was not statistically significant (p = 0.64 for computed axial length < 22.00 mm, p = 0.11 for computed axial length of 22.00 to 22.99, p = 0.81 for computed axial length of 23.00 to 23.99, and p = 0.03 for computed axial length ≥ 24.00 mm). Conclusion: Axial length measured with an A-scan can be reliably approximated by using Surrell’s formula based on corneal length measurements.

Keywords

• axial length
• corneal diameter
• corneal slope
• biometry