Parylene also has unique advantages for eye implants. Parylene Coating For Medical Devices such as intraocular lenses used to replace defective natural crystals. They can also be applied to visual aids in patients with retinitis pigmentosa. Retinitis pigmentosa is an irreversible disease that destroys peripheral vision and leaves the patient with only central vision. There are two photoreceptors on the retina: rods and cones. The rod cells are concentrated in the periphery of the retina, and the cone cells are concentrated in the central part of the retina (ie, the macular area). Rod cells help us see images that enter the perimeter or side view. They also help with vision in dark environments and low-light environments. The cones allow us to perceive the color and see the fine details in the central field of view.
Rod cells and cones convert light stimuli into electrical impulses that are then transmitted to the brain to "see" the actual image. The most common feature of retinitis pigmentosa is the progressive degeneration of rods and cones. As the disease progresses, more and more rod cells become degenerated and their vision is gradually lost. Developers and research institutions of visual aid devices are looking for a way to stimulate nerve endings in the retina to reconstruct vision.
A device currently under development has a special camera that captures external images and converts the images into electrical signals that are then sent to the human eye (where the implant is located). The patient wears a signal processor and a pair of special glasses containing the camera.
The eyepiece assembly contains an inductive coil for transmitting signals to the human eye. The electronic components in the assembly are capable of converting the signals coupled by the coils into signals that are transmitted through the matrix of electrodes connected to the retina. The electrode matrix stimulates the retinal nerve to reproduce the base image, similar to a video display generated by a lattice excitation. The stimulated nerve endings then send a preliminary image to the brain through the optic nerve. The use of Parylene coatings in such applications can help the device designer in a number of ways.
The ocular implant is about the size of a matchstick, with electronic components and coils at one end and an electrode matrix at the other end. After the electronic components and coil ends are placed in the iris and pupil, the electrode matrix is placed close to the retina. The device works in the eyeball and must, therefore, have an impedance effect on the fluid in the eye. Parylene Coating protects the device from the physiology of the eye and protects the eyes from the device. The coating must be biocompatible to provide insulation and moisture barrier protection without affecting the size or stiffness of the implant.
The success of this technology is in the ability to generate and transmit electrical signals and reconstruct images. The Parylene coating is thin enough to not affect the flexibility of the device, allowing the device to be adapted to the curvature of the retina.
The device creates a sufficient contrast between light and dark to enable the patient to identify the surrounding environment and personnel. Although this technical ability is far from perfect, it can improve the quality of life of patients and give them more freedom than total blindness. As such devices are further refined, designers will find various ways to increase the density of these electrode matrices to improve the image.
The use of Conformal Coatings Parylene allows designers to design, test and improve smaller devices. Parylene coatings provide a biocompatible barrier that protects delicate devices and components, and their chemical inertness further benefits implantable devices and electronic components. The use of such coatings can help designers ensure that future devices will perform their functions even in the harsh environment of the body.