The elastic properties of the eyewall, the effect of focal pressure on the retina, and the development of reversible bioadhesives for utilization in a retinal prosthesis

2011-08-08Degenerative retinal diseases such as Retinitis Pigmentosa and Age-Related Macular Degeneration are leading causes of blindness. Retinal prostheses have been developed to bypass the degenerate photoreceptors and stimulate the viable bipolar and retinal ganglion cells. These prostheses are designed to apply electrical stimulation directly to the viable cells, creating an artificial version of sight in implanted patients. Epiretinal prostheses utilize a polymer electrode array, which is affixed to the inner limiting membrane of the retina, using a retinal tack. The electrode array and tack creates varying focal pressure across the interface and subsequent retinal damage. In order to assist bioengineers to make design changes that can minimize these effects, firstly the elastic properties of the eyewall tissues must be accurately established. These properties can be utilized in computerized modeling (Finite Element Analysis) of the interface and enable refinement of future array designs. Secondly, defining safe limits of the amount of focal pressure that the retina can withstand without significant pathological damage is equally important. Thirdly, the integration of reversible bioadhesives could allow intraocular arrays to maintain intimate contact with the retina and may eliminate the need for a retinal tack. ❧ I have defined the elastic properties of the porcine and human posterior ocular poles including the retina, choroid and sclera in both the vertical and horizontal meridian. I describe the biological effect of focal pressure on the retina and attempt to define safe limits for future designs. I have also developed and tested reversible bioadhesives that could be integrated into the intraocular electrode array, in order to eliminate the tack. We have implanted these adhesive biomaterials onto the retina of both rabbits and dogs. These bioadhesives may have multiple applications not only in ophthalmology, but in a wide variety of surgical implants. The potential benefits for the retinal prosthesis could include removing the need for the tissue destructive tack, a reduction in focal pressure effects, improved apposition of the intraocular array to the retina, minimization of the current required to stimulate neurons, extended battery life, diminished heat production, and ultimately improved visual acuity