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Acoustic Radiation Force for Noninvasive Evaluation of Corneal Biomechanical Changes Induced by Cross‐linking Therapy
Author(s) -
Urs Raksha,
Lloyd Harriet O.,
Silverman Ronald H.
Publication year - 2014
Publication title -
journal of ultrasound in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 91
eISSN - 1550-9613
pISSN - 0278-4297
DOI - 10.7863/ultra.33.8.1417
Subject(s) - medicine , stiffness , cornea , ophthalmology , in vivo , strain (injury) , elastic modulus , biomedical engineering , anatomy , materials science , composite material , microbiology and biotechnology , biology
Objectives To noninvasively measure changes in corneal biomechanical properties induced by ultraviolet‐activated riboflavin cross‐linking therapy using acoustic radiation force (ARF). Methods Cross‐linking was performed on the right eyes of 6 rabbits, with the left eyes serving as controls. Acoustic radiation force was used to assess corneal stiffness before treatment and weekly for 4 weeks after treatment. Acoustic power levels were within US Food and Drug Administration guidelines for ophthalmic safety. Strain, determined from ARF‐induced displacement of the front and back surfaces of the cornea, was fit to the Kelvin‐Voigt model to determine the elastic modulus ( E ) and coefficient of viscosity (η). The stiffness factor, the ratio of E after treatment to E before treatment, was calculated for treated and control eyes. At the end of 4 weeks, ex vivo thermal shrinkage temperature analysis was performed for comparison with in vivo stiffness measurements. One‐way analysis of variance and Student t tests were performed to test for differences in E , η, the stiffness factor, and corneal thickness. Results Biomechanical stiffening was immediately evident in cross‐linking–treated corneas. At 4 weeks after treatment, treated corneas were 1.3 times stiffer and showed significant changes in E ( P = .006) and η ( P = .007), with no significant effect in controls. Corneal thickness increased immediately after treatment but did not differ significantly from the pretreatment value at 4 weeks. Conclusions Our findings demonstrate a statistically significant increase in stiffness in cross‐linking–treated rabbit corneas based on in vivo axial stress/strain measurements obtained using ARF. The capacity to noninvasively monitor corneal stiffness offers the potential for clinical monitoring of cross‐linking therapy.