Abstract
Purpose :
Vision degrading myodesopsia (VDM) occurs when vitreous opacities cause clinically significant degradation in contrast sensitivity (CS) and visual quality-of-life (VQOL). Past studies demonstrated efficacy of quantitative ultrasound (QUS) in quantifying vitreous echodensities that correlated with CS and VQOL. However, prior QUS VDM studies utilized log-compressed envelope data which had two major drawbacks: 1) a limited ability to quantify the fundamental ultrasound (US) scattering properties of opacities that most affect CS and VQOL and 2) an inability to develop an absolute machine-independent QUS index. Advances in US scanner technology now permit access to raw radiofrequency (RF) data which we employed to compute system-independent QUS parameters that characterize the scattering properties of vitreous opacities.
Methods :
31 eyes from 18 patients (age ± years, 12 males) experiencing VDM had CS measured using Freiburg Acuity Contrast Testing. Vitreous was scanned with a 20-MHz annular array probe (B20, ABSolu, Quantel Medical, France). RF data were exported and data were processed to obtain backscatter coefficient (BSC) values and envelope statistic parameters. A total of 9 QUS parameters were generated that quantified scatterer size, concentration, and organization (Table 1). Linear and multi-linear regression were used to identify correlations between QUS parameters and CS.
Results :
Six QUS parameters relating to scatterer size and concentration correlated with CS (p ≦ 0.02 for each). Multi-linear regression analysis revealed significant correlations between the set of QUS parameters and CS (R = 0.66, p < 0.001 ). The parameters with the strongest correlation to CS were spectral slope (R = -0.46, p < 0.003), which relates to scatterer size, and effective acoustic concentration (R = 0.47, p = 0.007), which relates to scatterer number density and relative acoustic impedance.
Conclusions :
QUS parameters computed from RF data effectively quantified vitreous echodensities that correlate with CS. Unlike past QUS approaches to evaluate VDM, our method is based on the backscatter coefficient and envelope statistics which provides more accurate and robust measurements of acoustic scattering properties. Such system-independent QUS methods can provide information about the characteristics of vitreous opacities that most affect CS and VQOL, enabling new diagnostic approaches and evaluation of therapies.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.