The Bionic Human Eye
This report accounts the basic biological human eye, the preliminary stage of research and development for the prosthetic eyes. It includes the investigation of current research, on-going projects and future trends in the field of prosthetic eyes that are designed to restore and possibly enhances human vision.
History of the prosthetic eyes is being discussed, stating how the idea of prosthesis came about. The report also includes the current available solutions, prototypes and clinical trials for the on-going projects of the prosthesis eyes. However, there are also problems encountered by the current projects, some remained unsolved, while others proceed to another level of the research. It is widely funded by the government as this will help millions of patients who suffer from blindness to restore back their sight.
Finally, conclusions and predictions are withdrawn on where the technology is actually heading at the end of the report.
Imperfection due to injury or diseases affects one's life. Without light, one faces a total darkness in their world, say blindness or lost vision due to macular degeneration and retinitis pigmentosa or maybe other reasons which can be devastating at any age, some feel depressed; others may suffer severely psychologically as well as physically, some may have major impact on self-image, self-esteem and self-confidence. However, with the prosthetic eyes (bionic eyes) techniques and material available today, a path of vision is opened for sufferers to regain (or partially regain) such vision and maybe in aspect of gaining back confidence and natural appearance.
Prosthetic eye is a form of artificial eye or robotic eye which has been investigated scientifically since at least 1950s. There are two types of prosthesis eyes, one is ocular prosthesis where it is used to replace an absent natural eye but it does not solve the problem of vision lost and other one is visual prosthesis which partially regains or improves one's vision. The concept of visual prosthetic eyes came from the human eyes in biology where lights is transverse through the cornea, the tiny opening of the eyes, pupil, the humour chamber until it reaches the retina which contains numerous of light-sensitive photoreceptors cells; these cells absorb photons and stimulated the nerve cells, it will then be transmitted to the optic nerve and finally sent pulses to the brain for reconstruction of images.
When artificial and electronics parts are brought together with the optical system, a visual prosthetic eye can be made, it usually has a basic idea of using externally-worn camera where images/signals will be transmitted to a chip implanted on the retina; which will then stimulated the retina ganglion cells by electrodes found inside the chip. This will help in transmitting visual information via the optic nerve into the brain for reconstruction of the original image. Researches and development of these bionic eyes have broadened such as artificial retina, contact lenses with integrated circuits, mini video-camera device placed directly onto the eyeball socket and some others, which helps to improve.
In order to achieve such high technology of artificial human eye, every difficulty and problem faced during the process should be taken into consideration. Therefore lengthy times are needed by the engineers, optician professionals and others to provide better solutions. More solutions are to come as the technology is advancing.
Basic Human Eye
Human beings each own a pair of eyes. The Eye is an organ which provides vision to the surroundings. The eye has a dynamic ability to adjust to a very wide range of light levels; it can view images at a wide range of distances from a few centimetres to infinity. It can also distinguish shades of colour in a 3-D space.
The eyeball is almost spherical with a diameter of about 22-24mm and contains jelly-like mass surrounded by a tough skin which is opaque except the front. In front, there is a bulge on the surface of the eyeball which forms the cornea; it has a refractive index of 1.38, causing the most of the bending of incident rays of light in the interface between air and cornea. Clear watery liquid called aqueous humour having refractive index of 1.34 is found behind the cornea. Iris is immersed in the aqueous humour which is in front of the lens; it gives an individual's eyes their pattern and colour; it adjusts the diameter of the aperture (pupil) by contracts or expands in response to the light intensity.
The lens has a refractive index of 1.39-1.41; it is an elastic membrane thereby the focal length of the lens can be adjusted by tension in the surrounding ciliary muscles, either by relaxation or contraction. The eyes analyses light by focusing wavefronts from different directions on to different parts of the retina. Accommodation is the ability of the eye to change its effective focal length to image objects over a range of distances. The two focusing elements of human eye: the cornea has a fixed power of about 40 dioptres while the lens which is adjustable can brings the total power to around 60 dioptres. When the muscles are relaxed, the lens will be flattened and little bending of rays occurs, hence, distant object are in focus and vice-versa. Perfection is impossible, some people may have defects; the common cases are short sightedness (myopia) and long sightedness (hypermetropia), without correction the cornea and lens of the myopia eye bring rays from a distant object to a focus in front of the retina, however, they can be corrected using a diverging (concave) and converging (convex) lenses respectively or even advanced medical services like LASIK; for a more unfortunate cases where patient lost their vision due to disease, illness, accident or other reason, hopes are given for blinds to partially regain their vision by using prosthetic eye which will then be discussed later on.
A relatively large chamber filled with vitreous humour with a refractive index of 1.34 can be found behind the lens. Light transverses through this humour before reaching the retina which is made up of an array of light-sensitive photoreceptor cells called rods and cones (refer appendix 1). Human Eyes have a complex optical system that detects visual lights of different strengths and wavelengths via the rod and cone cells in the retina which are used for vision. The different level of strengths in light can be interpreted as the brightness whereas different wavelengths can be conducted as colours. Rod cells are sensitive at low light intensity/dim light thus they are responsible for the low-light monochrome vision. Cone cells require brighter light than Rods and they are responsible for the differentiation in colour. However, these cells are responsible for the light perception and vision including colours variation and perception of depth via absorbing photons and are closely related to nerve cells which transmit visual information to the optic nerve, and then sent pulses to the brain to interpret and construct images. Technology uses this basic concept of visual transmission of human optical system to create a bionic eye.
History and development of prosthetic eyes
During the ancient world, the eye was a symbol of life, therefore precious stones can be found on the deceased, for example in Egypt. The Romans likes to decorate their built statues with artificial eyes made of silver and precious stones.
Archaeologists have discovered a female remains with an artificial eye of about 5,000 years old in the desert on the border of Afghan and Iran which is believed to have live in ancient Arabia. This is the earliest prosthetic eye ever found in the history. However, the uses of precious stones and gold to become an artificial eye cannot take the form of a natural human eye; it is too impractical and heavy to be worn as well. Until 1579, the Venetians came up with an idea of making the prosthetic eyes from glass but they were still being heavy and uncomfortable to be worn. In 1835, the Germans introduced the first hollow glass eye which is much lighter and comfortable to be worn. A lot of glass eyes were being manufactured and the pre-made eye was then utilised, however the hollow glass eye could implode due to the body acids corroding the glass and changes in temperature.
Since the outbreak of World War 2, exportation of this German glass was terminated but this brought about the development of plastic eye and has been the preferredmaterial for artificial eyes around the world because it is very tough and can be modified easily.
Prosthetists/ocularists are able to restore the loss to its natural appearance in match and mobility of one individual using the methods, materials and technologies available today. They can mimic an artificial eye from the other eye of the patient to the finest possible. However this does not resolve the lost in vision. Many scientific researchers/engineers are interested on visual prosthetic in order to regain the lost vision of the patient in the future.
Investigation by having interfaces between electronics and at the level of retina and optic nerve has been going on. Nowadays, millions of people suffering from retinitis pigmentosa are given hopes as studies have demonstrated restoration of partial vision by using early trails of retinal implants on several patients.
Current solutions, prototypes and clinical trials
The technology today has at least three firms that produce eye implants that stimulate the retinal cells. There may be slight differences in the implants from each firms, however, they all are having the same aim to regain one's vision and enable patient to regain independence. While there are many others having research and on-going project to make these prosthetic eyes better for the future.
The artificial retinal system from USA firm Second Sight having both Argus I & II and currently still working on the third version of the Argus technology. The Argus I had only 16 electrodes on the chip while Argus II has 60 electrodes which generated better and higher resolution images in the brain. Argus II is by far the best-known and widely used in clinical testing, having three components in the system; first in line is eyeglasses embedded with a camera, the video captured by the camera is sent wirelessly via transmitter that processes the video signal to the second component, an antenna implanted in the eye which is connected to an array of electrodes that have been implanted directly on top of the degenerated retina. The electrodes then activate the retina ganglion cells which then transmit visual information via optical nerve into the brain's vision centres (refer to appendix 2). Patient may need to scan the focused objects or surroundings for a while in order to produce a series of light and dark dots/spots that correspond to the original visual information from the external eyeglasses.
Clinical trials for the first generation of Argus I device were being used in 2002 and 2004, trials were successfully implanted onto six patients and helped them to partially restore sight; now they are able to detect light and motion, make out large letters and distinguish objects. In April 2009, Moorfields Eye Hospital in London implanted Argus II devices as part of clinical trial onto the retinas of the two pigmentosa patients who had almost lost their vision. Later on, it was being carried out on around 20 patients at various hospitals in Europe, the US and Mexico. Since there is no complaints from any hospital about the trials, it is believes to have reason for optimism of the prosthetic eye. Argus II will give finer resolution by generating about four times as many signals than Argus I; it proves to enable patients to have their vision partially restore, however it is still a long way from fully curing the blindness.
MIT's Retinal Implant is another type of artificial retina system which has the same principal as the Argus system. The differences are that MIT retina may have a superior casing structure made of titanium and the electrodes of this system are not attaching directly on the retina in order to avoid/reduce the risk of tearing during implantation. However, during testing of at least 10 months in pig eyes, it was proven to be safe. Soon the implants will have clinical trials on patients.
The German company Intelligence Medical Implants introduces a device called the Learning Retinal Implant System. It has the same three components in the system as Argus system but with additional of a learning software which enable the response to be regulated during learning phase. Evidence from trials brought up that this system results in better vision.
Another US company, Optobionics has a different structure from the other two firms, it has no external components but a smaller solar-powered microchip which is wireless and does not need any external power source are being implanted behind the retina, through a small surgical incision. The surgery procedures for this implant are very complicated.
Other on-going project includes Microsystem-based visual prosthesis; making use of a spiral cuff electrode around the optic nerve which is connected to a stimulator implanted in a small depression in the skull which then transmits signals from externally-worn camera to stimulate the optic nerve directly.
Implantable Miniature Telescope is a tiny prosthetic implanted into the patient's eye who suffered from age-related eye degeneration. It helps to restore central vision by projecting the image onto a broader surface of the retina that surrounds the macula (part of the retina responsible for highly detailed central vision) instead of the damaged macula. It can only be implanted into one eye of the patients with macular degeneration as both central and peripheral visions are important functions of the visual system. Peripheral vision is responsible for low-light vision; therefore the patients can get a better view during both day and night. Phase II/III clinical trials on this system has recently completed and proved that it doubled the vision of 2/3 of patients' eyes after one year with the implant.
Eyeborg project was found by Rob Spence who lost one of his eyes together with few individuals, came up with an invention of a functioning camera eye. With this invention, it actually does not give any sight back to the patient but it is able to do recording continuously throughout the patient's life as long as the battery operates. His prosthetic eye was modified to a camera eye with a tiny CMOS camera of about 1.5mm2, a lithium polymer battery and a wireless transmitter. The video signals can be sent wirelessly from the RF transmitter and it can be viewed on computer or television nearby. It can also be recorded to a storage device like a memory card.
Ocular prosthetic eyes were not able to move in the past. Today, Scott Garonzik, an ocularist has introduced a Magnetic attraction system for prosthetic eye wearers. With this system, it increases the mobility of the prosthetic eye so it looks more natural. It would be perfect to include this technology with visual prosthetic eyes, so it does not look awkward at all.
Difficulties of achieving a 'bionic eye' and solutions
Several problems of the Argus system, for Argus I, the images produced are low resolution images therefore the company upgraded the array of electrodes to around 60 which give a better and higher resolution images in Argus II. The problems encountered are never ending as in Argus II, the images are monochrome but the company believes that in the future, the company will be able to develop a third generation of Argus containing around 1,000 electrodes which aims to give back full sight to patient and might as well produce colour images. The implant does not work immediately; it requires time and training for the patient to make an adjustment for normal vision. However, this technology depends on both healthy optic nerve and the brain's visual centre, thus it is unable to treat blindness caused by glaucoma, damages of optic nerve or by stroke in the visual cortex and even blindness since birth, since the brain loses(or without) the ability to process optical signals into images.
Other than the Argus system, some other artificial retina for the bionic eyes also requires several years to becoming widespread around the world because it is too expensive, particularly for situations/countries that operation is not covered by health insurance.
For the eyeborg project, the biggest problem encountered is the power supply for the camera and wireless transmitter, but with a custom-made lithium polymer battery and a camera with a built-in transmitter, the problem is solved. Other than that, there is a possibility that the battery liquid or other chemicals leaking inside the prosthetic eye.
For the time being, the bionic eyes are too awkward to be seen and too fragile to withstand decades of wear and tear. Some patients have experienced side effects like inflammations, infections or intraocular pressure due to carelessness in surgery procedure but not the implant itself in most of the cases.
Conclusions and Predictions
Through clinical trials, the companies are able to understand the mechanism of each implant further more. If one is failed, there is other alternative by combining with other technologies, for example, installing memory coding and face recognition software in the prosthetic eye might help to identify a person much faster. For the eyeborg project, it would be better if the video signals from the transmitter can be transmitted to the optic nerve via a microchip and then to the brain's visual centre. Maybe they can try to work and combine with the idea of the Argus system and the MIT retinal project.
All the implants introduced are by far useful during daylight or presence of light, with the presence of the night vision goggle, it is wise to be used in a prosthetic eye in the future, and thus provide a better view during the night. Some company can try equipping the prosthetic eyes with LED which would be great for parties or act as source of lights when surrounding is dark, perhaps having laser light from the eye would be great during presentations. With infer-red sensor attached into the prosthetic eye may be helpful to detect the presence of others. Otherwise by putting distance detection sensor or sensors into the prosthetic eye to measure distance and detect any obstacles around which are better than scanning the surroundings for a while to reconstruct the image in the brain. However, the prosthesis eyes are small enough, the problems arise again if all these gadgets are to insert into it.
Retinal Imaging Display glasses could project supplemental information into your field of vision to augment your normal vision where the images are transparent enough, that does not interfere with the real visual field of what you are seeing (just like terminator in movies) but this technology still needs several more years of innovation before it is ready to break out. With this idea, another high level of prosthetic eyes can be achieved, the glasses can be substituted with contact lenses or artificial cornea, an external light source is needed to projects light onto the retina (or artificial retinal implant) and thus the patient can zoom in and out of his view and get a lot of information on the targeted obstacles (refer to appendix 3).
With the limited sources, it can only be imagined how the future prosthetic eye going to be, it may involve a GPS system to give directions for the patient while walking or driving. It may also be able to connect to the car's speedometer and fuel level so as to check on the speed limit and will be easily noticed by patient if the tank is empty via the Bionic Eye.
Books and magazines references
Optics and Photonics, An Introduction by F.Graham Smith and Terry A.King , from library.
IET magazine on eye sight special bionic eyes, future contact lenses edition. (Vol4, issue8, 9May-22May 2009).
Slve Stenstrm, Optics and the Eye BUTTERWWORTHS (1964), from library.
Microwave and optical transmission, A.David Olver, from library.
 Power in dioptres= 1/f, where the focal length f is in metres.