Showing papers by "Mark S. Humayun published in 2001"

Devices for intraocular drug delivery

Abstract: A therapeutic agent delivery device that can allows is particularly suitable for delivery of a therapeutic agent to limited access regions, such as the posterior chamber of the eye and inner ear. Preferred devices of the invention are minimally invasive, refillable and may be easily fixed to the treatment area. Preferred delivery devices of the invention also include those that comprise a non-linear shaped body member housing one or more substances and a delivery mechanism for the sustained delivery of the one or more substances from the non-linear shaped body member to the patient.

Intraocular retinal prosthesis

Abstract: PURPOSE: An electronic implant that can bypass the damaged photoreceptors and electrically stimulate the remaining retinal neurons to restore useful vision has been proposed. A number of key questions remain to make this approach feasible. The goal of this thesis is to address the following 2 specific null hypotheses: (1) Stimulus parameters make no difference in the electrically elicited retinal responses. (2) Just as we have millions of photoreceptors, so it will take a device that can generate millions of pixels/light points to create useful vision. METHODS: For electrophysiologic experiments, 2 different setups were used. In the first setup, charge-balanced pulses were delivered to the retinal surface via electrodes inserted through an open sky approach in normal or blind retinal degenerate (rd) mice. In the second setup, the rabbit retina was removed under red light conditions from an enucleated eye and then maintained in a chamber while being superfused with oxygenated, heated Ames media. In both setups, stimulating electrodes and recording electrodes were positioned on the retinal surface to evaluate the effect of varying stimulation parameters on the orthodromic retinal responses (i.e., recording electrode placed between stimulating electrodes and optic nerve head). For psychophysical experiments, visual images were divided into pixels of light that could be projected in a pattern on the retina in up to 8 sighted volunteers. Subjects were asked to perform various tasks ranging from reading and face recognition to various activities of daily living. RESULTS: Electrophysiologic experiments: In a normal mouse, a single cycle of a 1-kHz sine wave was significantly more efficient than a 1-kHz square wave (P < .05), but no such difference was noted in either of the 8- or 16-week-old rd mouse groups (8-week-old, P = .426; 16-week-old, P = .078). Charge threshold was significantly higher in 16-week-old rd mouse versus both 8-week-old rd and normal mouse for every stimulus duration (P < .05). In all groups, short duration pulses (40, 80, and 120 microseconds) were more efficient in terms of total charge (the product of pulse amplitude and pulse duration) than longer (500 and 1,000 microseconds) pulses (P < .05). In all groups, applying a pulse train did not lead to more efficient charge usage (P < .05). Psychophysical experiments: In high-contrast tests, facial recognition rates of over 75% were achieved for all subjects with dot sizes of up to 31.5 minutes of arc when using a 25 x 25 grid with 4.5 arc minute gaps, a 30% dropout rate, and 6 gray levels. Even with a 4 x 4 array of pixels, some subjects were able to accurately describe 2 of the objects. Subjects who were able to read the 4-pixel letter height sentences (on the 6 x 10 and 16 x 16 array) seemed to have a good scanning technique. Scanning at the proper velocity tends to bring out more contrast in the lettering. The reading speed for the 72-point font is a bit slower than for the next smaller font. This may be due to the limited number of letters (3) visible in the window with this large font. CONCLUSIONS: Specific parameters needed to stimulate the retina were identified. Delineating the optimum parameters will decrease the current requirements. Psychophysical tests show that with limited pixels and image processing, useful vision is possible. Both these findings should greatly simplify the engineering of an electronic retinal prosthesis.

Device and method for manual retinal vein catheterization

Abstract: A microcatheter system that allows for vascular infusion into retinal veins for extended periods of time. The microcatheter system includes a flexible cannula that is inserted into the retinal vein lumen and that remains stably within the retinal vein lumen without being held by a robot, micromanipulator or similar holding devices. The microcatheter system is particularly suitable for the treatment of retinal venous occlusive disease.

Light-driven retinal ganglion cell responses in blind rd mice after neural retinal transplantation.

Abstract: PURPOSE. Light-elicited retinal ganglion cell (RGC) responses after fetal neural retinal transplantation have not been demonstrated in animal or human subjects blind from outer retinal degeneration, despite apparent morphologic success. This study was designed to test the hypothesis that the functional success of retinal transplantation may be enhanced by using a young host retina (13 days old). METHODS. At postnatal day (P)13 C3H/HeJ (rd/rd) retinal degenerate mice received a subretinal transplant, in one eye only, of neural retinal tissue isolated from newborn normal C57/BL6J mice. Between 33 and 35 days after transplantation, local electroretinograms (ERGs) and ganglion cell responses were recorded directly from the retinal surface using a differential bipolar surface electrode. Measurements were performed both with and without light stimulation. Similar recordings were also performed in age-matched eyes subjected to sham transplantation, in control eyes that were not subjected to surgery, and in animals eyes that underwent transplantation at 8 weeks of age. After the recordings, the eyes were processed for light and transmission electron microscopy. RESULTS. Three of 10 mice showed bursts of ganglion cell action potentials (ON response only) as well as recordable intraocular ERGs over the transplant in response to 1-second and 200-msec light stimuli. Light-driven ganglion cell responses could not be recorded in areas outside the transplant in all transplant-recipient eyes, age-matched control eyes, and sham-transplantation eyes. Light responses also could not be recorded in animal eyes that received transplants at an older age (8 weeks). Electron microscopic examination confirmed the presence of photoreceptor outer segments in the areas affected by transplantation. CONCLUSIONS. This study demonstrates the presence of light-driven ganglion cell responses after subretinal transplantation in a retinal degenerate model. This finding may reflect functional integration of the transplant with the host, but a rescue effect on remaining host photoreceptors cannot be ruled out. The findings suggest, however, that modification of host parameters, such as host age, may be important approaches for improving the functional success of retinal transplantation.

Elevated vitreous concentration of monoclonal immunoglobulin manifesting as schlieren in juvenile rheumatoid arthritis-associated uveitis.

Abstract: We report the clinical findings and analysis of the immunoglobulin (Ig) composition of the vitreous of a 10-year-old girl with juvenile rheumatoid arthritis–associated uveitis. The vitreous had a schlieren appearance at the time of pars plana lensectomy and vitrectomy. Analysis of the vitreous fluid revealed marked elevation of IgG, IgM, IgA, and albumin levels relative to vitreous fluids from control patients without uveitis. The immunoglobulin coefficients were also elevated for the IgG and IgM classes of immunoglobulins. Immunofixation electrophoresis of the vitreous fluid revealed 2 distinct bands of restricted electrophoretic mobility. These studies suggest that there may be local (intraocular) production of immunoglobulins as an immunologic response in ocular inflammatory diseases such as juvenile rheumatoid arthritis–associated uveitis and that this immunologic response may be monoclonal (possibly biclonal or oligoclonal) in nature.

Towards a completely implantable, light-sensitive intraocular retinal prosthesis

Abstract: A completely implantable, light-sensitive retinal prosthesis must include the capability for both phototransduction and stimulus current generation, two power intensive functions. These devices will be implanted in the eye, creating a significant source of heat that must be dissipated by the ocular tissue without damaging the retina. However, significant technological hurdles remain. The amount of heat that can be safely dissipated by the eye and surrounding head without harming the retina, depends significantly on the position of the heater. Technology for, a high-density electrode array is advancing, but high-quality wires of biocompatible material in dimensions usable for a retinal prosthesis material have yet to be achieved.

Application of photosynthesis to artificial sight

Abstract: Using the technique of Kelvin force microscopy, we have performed the first measurements of photovoltages from single photosynthetic reaction centers. The measured values, typically 1 V or more, are sufficiently large to trigger a neural response. The goal of this project is insertion of purified Photosystem I (PSI) reaction. centers or other photoactive agents into retinal cells where they will restore photoreceptor function to people who suffer from age-related macular degeneration (AMD) or retinitis pigmentosa (RP), diseases that are the leading causes of blindness world-wide. Although the neural wiring from eye to brain is intact, these patients lack photoreceptor activity. It is the ultimate goal of this proposal to restore photoreceptor activity to these patients using PSI as the optical trigger. In principle, the approach should work. PSI is a robust integral membrane molecular photovoltaic device. Depending on orientation, it can depolarize or hyperpolarize the cell membrane with sufficient voltage to trigger an action potential.