High–Resolution Ultrasound Spectral and Wavelet Analysis of the Choroid in AMD

Abstract

Abstract: : Purpose: Age related macular degeneration (AMD) is the leading cause of blindness in people over 65 in the developed world. Several new therapies to slow or stop choroidal neovascularization are currently undergoing extensive clinical evaluation, but are limited by present imaging techniques. High–resolution 20 MHz ultrasound is a unique new method that permits high resolution imaging of the entire retina and choroid and can be used to study changes in choroid architecture that supplement standard clinical measures. This study evaluates changes in ultrasound backscatter in the non–exudative and the exudative form of AMD. Methods: Patients with ARM and AMD, seen in a university based practice, were recruited for high–resolution choroidal imaging in addition to fundus photography, FA and OCT exam of the retina. Digital RF scans of the macular region were acquired to examine backscatter changes in the retina, choriocapillaris and choroid. High resolution biometry of the retino–choroidal complex was performed and wavelet analysis ultrasound parameter images (WAUPI) were used to identify changes in scattering structure. Microarchiecture of vascular dimensions and thickness of the choroid can be accurately imaged and measured. Results: An overall shift in the distribution of choroidal backscatter size and concentration was seen in patients along with changes in the distribution of wavelet coefficients that denote increased disorder in the spacing of the choroidal vascular matrix. Increased boundary enhancement from protein and lipid deposition and thickening of Bruch’s membrane could be seen at the retinal choroidal boundary. Average choroidal thickness was seen to initially increase. The existence of focal areas of pigment epithelial detachment, disciform lesions, active neovascularization and geographic atrophy can modify this overall trend in some cases. Conclusions: High resolution choroidal imaging with spectral and wavelet analysis can provide additional information for examining the natural history of AMD and treatment monitoring. Larger scale studies are in progress to provide age–based population estimates of normal values to improve the efficacy of these ultrasound techniques.

Keywords: age-related macular degeneration • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • choroid: neovascularization