EC0271 BIONIC EYE (“Offers new hope of restored vision”)

[1]SOWMYA.U.L [2] KALYANI.D.P ICE-2/4 ICE-2/4 GNITS-Hyderabad GNITS-Hyderabad

BIONIC EYE (“Offers light at the end of tunnel for blind”)

Introduction:

Blindness is more feared by the people than any ailment except cancer and AIDS. The bionic eye is a bionic replacement part in the human body. Bionic eyes allow for advanced vision and repairs sight like a camera. Scientists are developing a bionic eye that may help to restore sight to people affected by two of the most common forms of blindness. They are:

1. Retinitis Pigmentosa 2. Age-Related Macular Degeneration.

In these diseases the photoreceptor cells slowly degenerate, leading to blindness. However, many of the retinal neurons that transmit signals from the photoreceptors are preserved for a prolonged period of time. The tiny implant employs technology similar to that of a digital camera. The device would contain an imaging detector with hundreds of pixels coupled to microscopic stimulating electrodes. If light forms an image on the detector, then the result will be electrical stimulation of the retina in the shape of this image. A bionic eye that can restore sight to the blind should be available commercially. The artificial retina has been cleared by US regulators to begin trials on between 50 and 75 people suffering from two of the most common causes of blindness, opening the way for millions more to benefit from similar implants in the future. If the research progresses well, a device could be on the market early in 2009.

 An early version of the prosthetic retina has already been fitted to six patients with retinitis pigmentosa, a degenerative and incurable eye condition that affects 1 in 3,500 people. All have recovered the ability to detect light and motion, and even to make out large letters and to distinguish between objects such as a cup, a knife and a plate.  The second-generation device that is now starting trials should provide even better vision, as it contains 60 light-sensitive electrodes, compared with 16 in the previous model.  More improvements are expected within five to seven years with a 1000-electrode implant that will enable previously blind people to recognize faces.

“The ultimate aim is to allow people recognize faces, and to allow the completely blind to get around on their own.”

Specifications:

This diagram shows the functioning of a bionic when arranged in a human eye.

BIONIC EYE TECHNOLOGY

1: Camera on glasses views image 2: Signals are sent to hand-held device 3: Processed information is sent back to glasses and wirelessly transmitted to receiver under surface of eye 4: Receiver sends information to electrodes in retinal implant 5: Electrodes stimulate retina to send information to brain

History:

Scientific research since at least the 1950s has investigated interfacing electronics at the level of the retina, optic nerve, thalamus, and cortex. Visual prosthetics, which have been implanted in patients around the world both acutely and chronically, have demonstrated proof of principle, but do not yet offer the visual acuity of a normally sighted eye.

Biological considerations:

The ability to give sight to a blind person via a bionic eye depends on the circumstances surrounding the loss of sight. For retinal prostheses, which are the most prevalent visual prosthetic under development (due to ease of access to the retina among other considerations), vision loss due to degeneration of photoreceptors (retinitis pimentosa, choroideremia, geographic atrophy macular degeneration) is the best candidate for treatment. Candidates for visual prosthetic implants find the procedure most successful if the optic nerve was developed prior to the onset of blindness. Persons born with blindness may lack a fully developed optical nerve, which typically develops prior to birth.

Technological considerations:

Visual prosthetics are being developed as a potentially valuable aide for individuals with visual degradation. The visual prosthetic in humans remains investigational.

Field of View:

 The first implant had just 16 electrodes on the retinal pad and, as a result, visual information was limited.  The new device has 60 electrodes and the receiver is shrunk to one-quarter of the original's size. It is now small enough to be inserted into the eye socket itself. The operation to fit the implant will also last just 1.5 hours, down from 7.5 hours.  Currently recipients of the device experience a relatively narrow view, but more electrodes should provide a greater field of vision.  By stimulating more ganglion cells, one can hope that visual acuity will increase dramatically. Hence, scientist’s next goal is to design a device with 1000 electrodes.  Regaining sight has felt like a miracle to those involved in the preliminary trial. At the beginning, it was like seeing assembled dots - "now it's much more than that."  People, whose blindness results from a range of causes, including retinitis pigmentosa and macular degeneration could benefit from it.  Although not truly an active prosthesis, an Implantable Miniature Telescope is one type of visual implant that has met with some success in the treatment of end-stage age-related macular degeneration.  This type of device is implanted in the eye's posterior chamber and works by increasing (by about three times) the size of the image projected onto the retina in order to overcome a centrally-located scotoma or blind spot.  Brain change: The new implant has a higher resolution than the earlier devices, with 60 electrodes. It is also a lot smaller, about one square millimeter, which reduces the amount of surgery that needs to be done to implant the device.  The technology has now been given the go-ahead by the US Food and Drug Administration to be used in an exploratory patient trial.  Using space technology, scientists have developed extraordinary ceramic photocells that could repair malfunctioning human eyes.

Capabilities:

The idea of a bionic eye might sound like something out of science fiction. Instead it is serious research that is going on.

 Bionic eye encompasses both night vision (zero moon illumination) and infrared (IR) capabilities with auto focus 20/15 clarity at all distances.  Automatic adjustment to all light levels.  Flash resistant.  Biological eye will be banked and replaced at the end of member’s service.  Fifteen year internal power source based on normal combat age range.  Selected units with night missions, voluntary receiver and mandatory removal.  Enables IR identification of friendly forces.  Limited battery life ensures return for replacement of original eye.  This would be capable of producing an image similar to that of the LED display of a digital camera.

 This photo is a simulated comparison of normal vision (left),  Vision impaired by acute macular degeneration affecting the area of the retina responsible for detailed central vision (center) and  The vision of a person using the Implantable Miniature Telescope (right).

Functioning:

Rods and Cones. Millions of them are in the back of every healthy human eye. They are biological solar cells in the retina that convert light to electrical impulses -- impulses that travel along the optic nerve to the brain where images are formed. Without them, we're blind.

 Indeed, many people are blind -- or going blind -- because of malfunctioning rods and cones.  Retinitis pigmentosa tends to be hereditary and may strike at an early age, while macular degeneration mostly affects the elderly.  The tiny implant employs technology similar to that of a digital camera.  It works by mimicking the action of the retina, the lining at the back of the eye that converts light into signals to the brain.  The implant translates light into electrical impulses and stimulates the retina, fooling the brain into thinking the damaged eye works.  The device would contain an imaging detector with hundreds of pixels coupled to microscopic stimulating electrodes. “If light forms an image on the detector, then the result will be electrical stimulation of the retina in the shape of this image.  The stimulated cells then send the information via the optic nerve to the brain.  The imaging part of the system is based upon the technology used in any digital camera.

When looking into someone's eyes, we can easily see several structures:

 A black-looking aperture, the pupil that allows light to enter the eye (it appears dark because of the absorbing pigments in the retina).

 A colored circular muscle, the iris, which is beautifully, pigmented giving us our eye's color (the central aperture of the iris is the pupil). This circular muscle controls the size of the pupil so that more or less light, depending on conditions is allowed to enter the eye. Eye color, or more correctly, iris color is due to variable amounts of eumelanin (brown/black melanins) and pheomelanin (red/yellow melanins) produced by melanocytes. More of the former is in brown eyed people and of the latter in blue and green-eyed people. The Melanocortin-1 Receptor Gene is a regulator of eumelanin production and is located on chromosome(MCIR) 16q24.3. Point mutations in the MCIR gene will affect melanogenesis. The presence of point mutations in the MCIR gene alleles is a common feature in light skinned and blue/green eyed people a transparent external surface, the cornea that covers both the pupil and the iris. This is the first and most powerful lens of the optical system of the eye and allows, together with the crystalline lens the production of a sharp image at the retinal photoreceptor level.

 The "white of the eye", the sclera, which forms part of the supporting wall of the eyeball. The sclera is continuous with the cornea. Furthermore this external covering of the eye is in continuity with the durra of the central nervous system.

When we remove the eye from the orbit, we can see that the eye is a slightly asymmetrical sphere with an approximate sagittal diameter or length of 24 to 25 mm. and a transverse diameter of 24 mm. It has a volume of about 6.5 cc.

A cross-sectional view of the eye shows:

 Three different layers;

1. The external layer, formed by the sclera and cornea 2. The intermediate layer, divided into two parts: anterior (iris and ciliary body) and posterior (choroid) 3. The internal layer, or the sensory part of the eye, the retina

 Three chambers of fluid:  Anterior chamber (between cornea and iris), Posterior chamber (between iris, zonule fibers and lens) and the Vitreous chamber (between the lens and the retina). The first two chambers are filled with aqueous humor whereas the vitreous chamber is filled with a more viscous fluid, the vitreous humor. The sagittal section of the eye also reveals the lens which is a transparent body located behind the iris. The lens is suspended by ligaments (called zonule fibers) attached to the anterior portion of the ciliary body. The contraction or relaxation of these ligaments as a consequence of ciliary muscle actions, changes the shape of the lens, a process called accommodation that allows us to form a sharp image on the retina. Light rays are focused through the transparent cornea and lens upon the retina. The central point for image focus (the visual axis) in the human retina is the fovea. Here a maximally focused image initiate’s resolution of the finest detail and direct transmission of that detail to the brain for the higher operations needed for perception. Slightly more nasally than the visual axis is the optic axis projecting closer to the optic nerve head. The optic axis is the longest sagittal distance between the front or vertex of the cornea and the furthest posterior part of the eyeball. It is about the optic axis that the eye is rotated by the eye muscles. Some vertebrate retinas have instead of a fovea, another specialization of the central retina, known as an area centralis or a visual streak.

Extraocular muscles:

http://webvision.med.utah. edu/imageswv/scan.jpegEach eyeball is held in position in the orbital cavity by various ligaments, muscles and facial expansions.

Inserted into the sclera are three pairs of muscles (6 muscles altogether). Two pairs are rectus muscles running straight to the bony orbit of the skull orthogonal to each other (the superior rectus, the inferior rectus, the lateral rectus and the medial rectus muscles). A further pair of muscles, the oblique muscles (superior oblique and inferior oblique) are angled as the name implies obliquely. These muscles, named extra ocular muscles rotate the eyeball in the orbits and allow the image to be focused at all times on the fovea of central retina.

Development of the eye:

The retina is a part of the central nervous system and an ideal region of the vertebrate brain to study, because like other regions of the central nervous system, it derives from the neural tube. The retina is formed during development of the embryo from optic vesicles out pouching from two sides of the developing neural tube. The primordial optic vesicles fold back in upon themselves to form the optic cup with the inside of the cup becoming the retina and the outside remaining a single monolayer of epithelium known as the retinal pigment epithelium. Initially both walls of the optic cup are one cell thick, but the cells of the inner wall divide to form a neuroepithelial layer many cells thick: the retina

Sensory retinal development begins as early as the optic vesicle stage, with the migration of cell nuclei to the inner surface of the sensory retina. Additional retinal development is characterized by the formation of further layers arising from cell division and subsequent cell migration. The retina develops in an inside to outside manner: ganglion cells are formed first and photoreceptors cells become fully mature last.

http://webvision.med.utah.edu/imageswv/5months.jpegFurther changes in retinal morphology are accomplished by simultaneous formation of multiple complex intercellular connections. Thus by 5 months of gestation most of the basic neural connections of the retina will be established.

The functional synapses are made almost exclusively in the two plexiform layers and the perikarya of the nerve cells are distributed in the three nuclear layers. Photoreceptor cell maturation begins with the formation of outer segments (OS) containing visual pigment from multiple infoldings of the plasma membrane of each cell. Outer segment formation proceeds and the eye become sensitive to light at about 7 months' gestation.

The final portion of the sensory retina to mature is the fovea, where the ganglion cell layer thickening begins during midge station. The outer nuclear layer is also wider here than elsewhere in the retina and consists almost entirely of developing cone cells. The ganglion cell nuclei migrate radially outwards in a circle, leaving the fovea free of ganglion cell nuclei. Cell-cell attachments persist, however and foveal cone cells alter their shape to accomodate the movement of ganglion cells. Foveal development continues with cell rearrangements and alteration in cone shape until about 4 years after birth

Surface membranes cover the eye cup and develop into lens, iris and cornea with the three chambers of fluid filled with aqueous and vitreous humors.

Surface membranes cover the eye cup and develop into lens, iris and cornea with the three chambers of fluid filled with aqueous and vitreous humors.

Retinal prosthesis has been for restoration of sight in patients suffering from degenerative retinal diseases such as Retinitis Pigmentosa and Age-Related Macular Degeneration. In these diseases the photoreceptor cells slowly degenerate, leading to blindness. However, many of the retinal neurons that transmit signals from the photoreceptors are preserved for a prolonged period of time. It has been shown that electric stimulation of retinal neurons can produce perception of light (“phosphenes”) in patients suffering from retinal degeneration. Current devices for retinal stimulation involve a very small number of electrodes (16), while thousands of pixels are required for functional restoration of sight. Spatial resolution and number of electrodes in the array are limited by such physical factors as divergence of electric field, electrochemistry at the metal-liquid interface and heating of the retina. Lateral spread of electric field, as well as threshold current required for cellular stimulation strongly depend on the distance between the electrodes and the target cells. For the pixel density geometrically corresponding to visual acuity of 20/400 (the level of “legal blindness”) the cells should not be farther away from electrodes than 60 micrometers, and for visual acuity of 20/80 this distance should not exceed 10 micrometers. Such stringent requirements of proximity between thousands of electrodes and their target cells preclude application of a flat array of electrodes for high resolution retinal stimulation on either epiretinal or sub retinal sides.

System Design: A video camera transmits 640x480 pixel images at 25-50 Hz to a pocket PC. The computer processes the data, and displays the resulting images on an LCD matrix of similar resolution, mounted on goggles worn by the patient. The LCD screen is illuminated with a pulsed near- infrared light, projecting the images through the eye and onto the retina. The IR light is then received by photodiodes on an implanted chip, which is approximately 3 mm in diameter. Each photodiode converts the IR signal into a proportional electric current using a common pulsed biphasic power supply driven by inductively-coupled Radiofrequency. Electrical stimulation by the chip Introduces visual information into diseased retinal Tissue, while any remaining peripheral vision responds normally to visible light passing through the transparent goggles.

Retinal Migration: Recently we discovered a phenomenon that may help to address the problem of proximity of Electrodes to cells. We observed a fascinating effect Of migration of retinal cells into the perforated Sub-retinal implant. Within a few days after Implantation neural retinal cells migrate into the Pores where stimulating electrodes can be positioned, while preserving their axonal connections to the retina above the implant. This way an intimate Proximity between electrodes and target cells is achieved automatically along the whole surface of the implant. Scanning Electron micrograph of the upper two layers of the lithographically fabricated array with the aperture sizes of 10 and 20 m, and chamber sizes of 40 m.

The effect of cellular migration can also be utilized with an implant having an array of thin protruding electrodes insulated at their sides and exposed at the tops. When positioned under the retina, the cells migrate into the spaces between the pillars thus assuring penetration of the electrodes into the retina without high pressure and associated risk of mechanical injury. The depth of penetration is determined by the length of the electrodes. The approaches based on pores and on protruding electrodes are complimentary: in the first case the actively migrating cells penetrating into the pores will be stimulated. In the second case the actively migrating cells move towards the bottom of an implant, while the electrodes approach the target cells which did not migrate. Scanning Electron micrograph of the lithographically fabricated array with the pillars of 10mm in diameter and 50mm in height.

Description of the device:

The bionic eye the device is a circle about the size of a five-cent piece, inserted into the eye where the retina sits.

"It is a silicon chip which decodes the radio signals and delivers the stimulations.” The chip sends messages to the retinal ganglion cells through small wires. The device receives signals from a pair of glasses worn by the patient, which are fitted with a camera.

The camera feeds the visual information into a separate image-processing unit, which makes 'sense' of the image by extracting certain features. It might find a door, for example, by contrasting the bright open door with a dark room.

The unit then breaks down the image into pixels and sends the information, one pixel at a time, to the silicon chip, which then reconstructs the image. Data is broadcasted into the body using radio waves. "It's like a radio station that only has a range of 25 millimeters."

Real-time vision:

The user wears a pair of glasses that contain a miniature camera and that wirelessly transmit video to a cell phone-sized computer in the wearer's pocket. This computer processes the image information and wirelessly transmits it to a tiny electronic receiver implanted in the wearer's head.

When received in the implanted chip, the digital information is transformed into electrical impulses sent into the ganglion cells. From there, the brain takes over as the information travels down the optic nerve to the visual cortex at the back of the brain. The whole process occurs extremely rapidly, so that patients see in real-time. This is important any noticeable lag could stimulate the "vestibular-ocular reflex", making people feel dizzy and sick.

Precautions:

 They should be careful while using these artificial eyes.  Especially, while wearing and removing them if they are for temporary use.  If using a permanent device, they should consult the prescribed doctor regularly for not facing any troubles.  Proper care should be taken while in water, close by to fire, in extremely hot conditions.

Advantages:  Automatic adjustment to all light levels.  Flash resistant.  Biological eye will be banked and replaced at the end of member’s service.  Fifteen year internal power source based on normal combat age range.  Selected units with night missions, voluntary receiver and mandatory removal.  Enables IR identification of friendly forces.  Limited battery life ensures return for replacement of original eye.

Disadvantages:

 High cost.  Hard to get the surgery done.  Tuff to maintain.

Conclusion:

We here by conclude that, this is a revolutionary piece of technology and really has the potential to change people’s lives. Bionic eye repairs sight like a camera and will let the blind see. So it would be a boon for every human with this defect of eye.

Sources:

Google search, Books related to Biometrics, Faculty.