An ultrasound-based biomarker of myopia in the guinea pig sclera

Abstract

Purpose : Raw ultrasound (US) data can be processed using quantitative US (QUS) methods to obtain biomechanical parameters associated with changes in tissue microstructure. In this study, QUS estimates were obtained from the posterior sclera in myopic guinea pigs (GPs) using an 80-MHz US system. We hypothesize that QUS estimates can provide an independently-measured, novel myopia biomarker that correlates with axial length (AL) and refractive error (RE).

Methods : 21 GPs underwent form deprivation (FD) in one eye from 5 to 20 days. At 20 days, intact, normotensive eyes were immersed, “levitated” in PBS and anchored in a nearly in vivo anatomic position with partial-thickness corneal sutures. 3D raw US data were collected by raster scanning with an 80-MHz transducer. The scan was centered at the posterior pole, and the data were processed to derive 12 QUS estimates in six regions of each eye. QUS estimates were linearly combined and correlated with ALs and REs measures.

Results : Figure 1a depicts results obtained from the right eye of a GP with -4.71D of induced relative myopia. 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 that provides the effective size of structures responsible for US scattering. A striking quantitative contrast is visible with lower ESD values in the superior sclera (blue outline) than in the inferior sclera (green). Figures 1b and 1c show correlation plots obtained using 4 QUS estimates to predict RE (R=0.816) and AL (R=0.791).

Conclusions : This study suggests that QUS methods could provide a new biomarker of scleral remodeling in myopia. High correlations were found between QUS-based prediction and independently-obtained biomarkers. Ultimately, QUS estimates are likely to be sensitive to microstructural changes in the posterior sclera during myopia development.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Figure 1: a) Illustrative QUS images obtained from a myopic right eye with vertical scans running 1 mm nasal to, 0.5 mm nasal to, and through the optic nerve head nasal edge. The color-coded information is the effective scatterer diameter. b) and c) Interocular differences(IOD) were calculated between the FD eye and the untreated fellow eye in each animal. IOD in refractive error and axial length were correlated with IOD in QUS estimates (best prediction with 4 parameters).