Application of acoustic radiation force in ophthalmic ultrasound

The vitreous body of the eye is a collagen gel supported by hyaluronic acid (HA) molecules. As one ages, HA diffuses out of the eye, eventually leading to collapse of the vitreous body. Resultant changes in the material and structural properties of the vitreous are associated with a variety of sight threatening conditions, including retinal detachment. Unfortunately these changes are often difficult to quantify or counteract other than through invasive surgery. The authors are developing non-invasive techniques which utilize ultrasonic radiation force to diagnose changes in the vitreous and to treat retinal detachments which result in part from degradation of the vitreous. The authors are currently developing a novel technique, known as Kinetic Acoustic Retinal Evaluation (KARE), which would non-invasively generate and image vitreal motion as a means of diagnosis and localization of a variety of vitreo-retinal disorders. KARE utilizes acoustic radiation force to generate small, localized displacements of the vitreous body. These displacements are quantified using either Doppler or speckle tracking algorithms. The authors present encouraging simulation and experimental results using excised porcine eyes. They also present simulation results which predict the risks of acoustic heating associated with this technique. They are also working to develop a two step method for non-invasive repair of retinal detachments. In the first step, a new technique known as Acoustic Retinal Manipulation (ARM) is applied to move the detached retina into contact with the retinal pigment epithelium. Next, standard techniques such as laser photocoagulation or cryopexy are used to form a lasting bond between the retina and underlying tissues. ARM utilizes both direct acoustic radiation force and acoustic streaming to displace the retina. The authors present initial experimental results acquired using retina mimicking material in a water tank and excised porcine eyes. They also present simulation results which predict the risks of acoustic heating associated with ARM.