Abstract
Purpose :
Chemical crosslinking (CXL) treatments offer a minimally invasive method of treating corneal ectasia and may also provide a method to halt the progression of myopia by strengthening the posterior sclera. Effective clinical use would require methods to evaluate longitudinal efficacy of CXL. Prior studies revealed the potential of quantitative ultrasound (QUS) to evaluate microstructural changes in the myopic posterior sclera. This study used QUS to monitor changes in sclera microstructure caused by CXL.
Methods :
Seven adult ex vivo porcine eyes were procured from a supplier and placed in a -80oC freezer for later use. Prior to data acquisition, eyes were thawed and excess tissue was removed from the posterior pole. Eyes were divided into control (3 eyes) and treated (4 eyes) groups. Control eyes were mounted in the experimental setup and immersed in room temperature phosphate buffered saline whereas treated eyes were immersed in 26mM sodium hydroxymethylglycinate (SHMG), a CXL agent. Eyes were scanned by an 80MHz ultrasound transducer at regular time intervals and the RF echo data were analyzed to compute ten QUS parameters: 5 from backscatter coefficient methods, 4 from envelope statistics, and shear wave speed (SWS) to infer tissue stiffness. Resulting QUS estimates were correlated with immersion time to evaluate the efficacy of QUS to monitor CXL treatment.
Results :
Among control eyes, a significant increase in value was measured for spectral intercept (I0, R2=0.94, p=0.01), midband fit (R2=0.91, p=0.01), and effective acoustic concentration (R2=0.88, p=0.02). When considering treated eyes, positive temporal changes were measured for spectral slope (R2=0.88, p=0.02) whereas significant decreases were observed for I0 (R2=0.86, p=0.02) and effective scatterer diameter (R2=0.89, p=0.02). SWS estimated by passive elastography showed a significant increase for treated eyes (R2=0.85, p=0.03) and no significant correlation with immersion time for control eyes (R2=0.09, p=0.63).
Conclusions :
QUS parameters estimated from high frequency ultrasound data are correlated with CXL-induced changes in scleral tissue microstructure. In addition, CXL leads to an increase in tissue stiffness that is measured as an increase in SWS. Results of this study provide preliminary evidence that high frequency QUS may be a useful tool for monitoring CXL treatment in a clinical setting.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.