Design and validation of a telemetrically drived implantable glaucoma drainage device

Glaucoma is one of the leading cause of irreversible blindness in the world and it usually occurs when the pressure inside the eyes gradually rises, permanently damaging the optic nerve. Medications and filtering surgery are two possible therapies available for patients suffering from this disease. In the same perspective, glaucoma drainage devices allowing a better outflow of the aqueous humor have been developed to address most of the problems present with the classic surgical techniques. However none of the implants currently available on the market have been able to date to address the problems related to the postoperative hypotony, the long-term fibrosis formation as well as the requirements to adjust filtration to the specific needs of the patients. In this context a new adjustable glaucoma drainage device is being currently developed that allows a continuous control of the outflow resistance. Its optimization and validation depends on previous outflow facility and resistance measurements. Thus 5 enucleated eyes from white New-Zealand rabbits have been perfused with a saline solution using a micropump before surgery and after implantation of a microtube (V-50 ${Ex-PRESS}^{TM}$). The resulting outflow facilities were respectively 0.35 and 1.31 $\mu$l/min/mmHg when the compliance was not altered by the filtering surgery and the microtube insertion. The tube composing the device showed a resistance equivalent to $23\times{10}^{-3}$ mmHg/$\mu$l/min with an internal diameter equal to 250 $\mu$m. From a theoretical point of view the linear relation between the adjustment of the resistance and the intraocular pressure has been verified. This relation was obtained by crushing the tube with a disc acting within the implant. The energy required to crush the tube was estimated to be at least ${10}^{-6}$ Nm. These results support the idea that the construction of an adaptable glaucoma drainage device is possible opening the doors to an automatically driven sensor device