Noninvasive estimation of the ocular elastic modulus for age-related macular degeneration in the human eye using sequential ultrasound imaging

Abstract

Introduction: Elastic modulus estimation may be an important clinical criterion, as it seems to affect such eye parameters as intraocular pressure, ocular pulsation, blood flow, effect of topical medications, and post-refractive surgery complications. The purpose of this study was to examine the differences in elasticity in the ocular axial length, posterior wall thickness (posterior pole), and retina-choroid thickness under normal and aged-related macular degeneration (AMD) conditions in the human eye by directly estimating the elastic modulus with sequential and noninvasive ultrasound image processing.

Materials and methods: In this study, 25 healthy subjects and 20 patients with non-neovascular AMD participated in the experiment. The deformation of the ocular axial length, posterior wall thickness and retina-choroid complex thickness was captured using high-resolution ultrasonography before and after loading. The B-mode (20MHz) and A-mode (8MHz) frames were obtained and processed with an echo tracking technique. The elastic modulus was estimated using changes in ocular axial length, posterior wall thickness and retina-choroid complex thickness and with applied stress measurements.

Results: There was a significant difference (p<0.05) in the ocular axial length elastic modulus between the AMD and healthy subjects (AMD patients: 95.165±26.431kPa, vs. healthy subjects: 49.539±25.867kPa). Moreover, there was a statistically significant difference (p<0.05) in the posterior wall thickness elastic modulus between AMD patients and healthy subjects (AMD patients: 50.519±12.295kPa, vs. healthy subjects: 20.519±11.827kPa). However, no statistically significant difference (p-value>0.05) was found in the retina-choroid complex elastic modulus between the two groups (AMD patients: 20.134±3.898kPa, vs. healthy subjects: 15.630±4.250kPa).

Conclusion: Although the results were obtained examining a relatively low number of patients, it would appear that noninvasive ultrasound estimation of the local elastic moduli of ocular axial length and posterior wall thickness is suited to aid in detection of the non-exudative AMD thus manifesting its potential as a screening tool in symptom-free individuals.