Quantitative-ultrasound assessment of the myopic sclera in the guinea pig

Abstract

Purpose : Quantitative ultrasound (QUS) permits estimation of QUS parameters associated with tissue microstructure and organization. In this study, QUS parameters were obtained using 80-MHz ultrasound (US) images from the posterior sclera in myopic guinea pigs (GPs). We hypothesize that QUS may provide a new and quantitative contrast mechanism that could ultimately assess ocular biomechanical properties in vivo.

Methods : US radiofrequency data were collected using a broadband 80-MHz transducer (Figs. 1a,b) from both eyes of GPs that had undergone form deprivation in the right eye (5-20 days). Intact, normotensive eyes were immersed, “levitated” in Dulbecco's phosphate buffered saline and anchored in a nearly in vivo anatomic position with partial thickness corneal sutures (Fig. 1c). With the transducer aimed at the posterior pole of the eye, a 2D scan centered at the optic nerve was acquired and the data were processed to derive several QUS parameters.

Results : Figure 1d depicts results obtained from an animal that had -7.24D of induced relative myopia (left +6.72D, right -0.52D). Specifically, it shows conventional US images augmented with color-coded information corresponding to the value of the effective scatterer diameter (ESD), which is a QUS parameter providing the effective size of the structures responsible for US scattering. A striking quantitative contrast is visible, with ESD values lower in the myopic right eye (9.0 +\- 0.50 µm) than in the contralateral control eye (10.4 +\- 0.50 µm, t-test, p<0.0001).

Conclusions : This study establishes that QUS methods may be sensitive to changes occurring in the posterior sclera during myopia. For example, US scattering could be dominated by collagen fibrils and QUS methods and ESD could potentially be sensitive to these structural changes. QUS may provide a new means of quantitatively assessing myopia progression, severity, and treatment efficacy.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Figure 1: a) Photograph of the 80-MHz QUS experiments, b) 80-MHz transducer above the posterior eye surface, and c) eye “levitating” in solution with the sclera essentially under zero tension, mimicking in vivo conditions. QUS images obtained from the control (d, bottom) and myopic (d, top) eyes. The color-coded information is the effective scatterer diameter, which shows contrast between thy myopic and control eyes.