Restoring a functional level of vision to people who are blind has been a dream of medicine for centuries. Although we are still far from restoration of high-resolution vision, bionic eye technologies are overcoming crucial bottlenecks and are slowly moving from the laboratory into the clinic and onto the free market.
Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, some people experience a gradual worsening of vision that may affect one or both eyes. While it does not result in complete blindness, loss of central vision can make it hard to recognize faces, drive, read, or perform other activities of daily life.
A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble with bright lights, and trouble seeing at night. This may result in trouble driving, reading, or recognizing faces. Poor vision caused by cataracts may also result in an increased risk of falling and depression. Cataracts cause half of all cases of blindness and 33% of visual impairment worldwide.
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex. It is separated by two cortices, by the longitudinal fissure that divides the cerebrum into the left and right cerebral hemispheres. The cerebral cortex is the largest site of neural integration in the central nervous system. It plays a key role in attention, perception, awareness, thought, memory, language, and consciousness.
Clinical trials are experiments or observations done in clinical research. Such prospective biomedical or behavioral research studies on human participants are designed to answer specific questions about biomedical or behavioral interventions, including new treatments and known interventions that warrant further study and comparison. Clinical trials generate data on dosage, safety and efficacy. They are conducted only after they have received health authority/ethics committee approval in the country where approval of the therapy is sought.
If an infant is born unable to see or with severe visual impairment, he is said to have congenital blindness. A number of different conditions can cause congenital blindness, including certain diseases and genetic factors. The term “congenital” simply means that it is present from birth, and does not provide information as to why a child might be born blind. These patients have reduced acuity, severe nearsightedness and involuntary movements of the eyes.
A cortical implant is a subset of neuroprosthetics that is in direct connection with the cerebral cortex of the brain. By directly interfacing with different regions of the cortex, the cortical implant can provide stimulation to an immediate area and provide different benefits, depending on its design and placement. A typical cortical implant is an implantable micro electrode array, which is a small device through which a neural signal can be received or transmitted. The goal of a cortical implant and neuroprosthetic in general is “to replace neural circuitry in the brain that no longer functions appropriately.”
Diabetic retinopathy, also known as diabetic eye disease (DED), is a medical condition in which damage occurs to the retina due to diabetes mellitus. Poorly controlled blood sugar is a risk factor and early symptoms include floaters, blurriness, dark areas of vision, and difficulty perceiving colors. It is a leading cause of blindness in many developed countries. Diabetic retinopathy affects up to 80% of those who have had diabetes for 20 years or more. At least 90% of new cases could be reduced with proper treatment and monitoring of the eyes. The longer a person has diabetes, the higher his or her chances of developing diabetic retinopathy. Each year in the United States, diabetic retinopathy accounts for 12% of all new cases of blindness.
Electrophysiology is the branch of physiology that studies the electrical properties of biological cells and tissues. It involves measurements of voltage changes, electrical currents, or manipulations on a wide variety of scales from single ion channel proteins to whole organs like the heart. In neuroscience, it includes measurements of the electrical activity of neurons, and, in particular, action potential activity. Recordings of large-scale electrical signals from the nervous system, such as electroencephalography, may also be referred to as electrophysiological recordings. They are useful for electro diagnosis and monitoring.
Epiretinal implants are placed on top of the retinal surface, above the nerve fiber layer, directly stimulating ganglion cells and bypassing all other retinal layers. Array of electrodes are stabilized on the retina using micro tacks which penetrate into the sclera.
Glaucoma is a group of eye diseases which result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle glaucoma, in which the drainage angle for fluid within the eye remains open, with less common types including closed-angle glaucoma and normal-tension glaucoma. Open-angle glaucoma develops slowly over time and there is no pain. Closed-angle glaucoma can present gradually or suddenly. Vision loss from glaucoma, once it has occurred, is permanent. Risk factors for glaucoma include increasing age, and use of steroid medication. If treated early, it is possible to slow or stop the progression of disease with medication, laser treatment, or surgery. The goal of these treatments is to decrease eye pressure.
Hemianopia, sometimes called hemianopsia, is partial blindness or a loss of sight in half of your visual field. It's caused by brain damage, rather than a problem with your eyes.
Late blindness refers to individuals who developed blindness at a later stage in life, after childhood. Late blindness as compared to early blindness may have the disadvantage of not having as much time to adjust and heighten connections of the sight, hearing, and touch centers of the brain to make up for vision loss.
The lateral geniculate nucleus (LGN) is a relay center in the thalamus for the visual pathway. It receives visual information from the retina and sends it to the visual cortex for processing. It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve. There are two LGNs, one on the left and another on the right side of the thalamus. The LGN receives information directly from the ascending retinal ganglion cells via the optic tract and from the reticular activating system. Neurons of the LGN send their axons through the optic radiation, a direct pathway to the primary visual cortex. In addition, the LGN receives many strong feedback connections from the primary visual cortex. In humans as well as other mammals, the two strongest pathways linking the eye to the brain are those projecting to the dorsal part of the LGN in the thalamus, and the superior colliculus. .
Legal blindness is when vision is 20/200 or less in your better eye or your field of vision is less than 20 degrees. The American government uses the term “legal blindness” to decide who can get certain benefits, like disability or job training.
The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. It is located at the rear end of the brain and is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The occipital lobe is divided into several functional visual areas. Each visual area contains a full map of the visual world. Although there are no anatomical markers distinguishing these areas, physiologists have used electrode recordings to divide the cortex into different functional regions.
The optic nerve is a paired cranial nerve that transmits visual information from the retina to the brain. It connects the eye to the brain and transmits all visual information including brightness perception, color perception and visual acuity. It extends from the optic disc to the optic charisma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus. In most mammals, optic nerve damage results in irreversible blindness. The fibers from the retina run along the optic nerve to nine primary visual nuclei in the brain, from which a major relay inputs into the primary visual cortex. The optic nerve is composed of retinal ganglion cell axons and glia.
Optogenetics is a biological technique that involves the use of light to control neurons that have been genetically modified to express light-sensitive ion channels. As such, optogenetics is a neuromodulation method that uses a combination of techniques from optics and genetics to control the activities of individual neurons in living tissue- even within freely-moving animals.
Partially sighted indicates some type of visual problem that may require special education services such as readers, audio taped texts, and raised-line drawings. A partially blind individual may meet the challlenge of disability in the same way as a totally blind individual.
A phosphene is the phenomenon of seeing light without light actually entering the eye. Many patients have reported phosphenes as bright circular or streaky spots of light among darkness. Phosphenes can be directly induced by mechanical, electrical, or magnetic stimulation of the retina or visual cortex, or by random firing of cells in the visual system. Visual neuroprostheses have been found to stimulate phosphenes to restore vision to people with severe visual impairments. Most vision researchers believe that phosphenes result from the normal activity of the visual system after stimulation of one of its parts from some stimulus other than light.
The primary visual cortex, also known as V1, Brodmann area 17, or the striate cortex, is the most studied visual area in the brain. It is a structure that is essential for conscious processing of visual stimuli. In mammals, it is located in the posterior pole of the occipital lobe and is the simplest, earliest cortical visual area. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and then reaches the visual cortex. It is highly specialized for processing information about static and moving objects, among other things.
A retinal ganglion cell (RGC) is a type of neuron located near the inner surface (the ganglion cell layer) of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and amacrine cells. RGC’s collectively transmit image-forming and non-image forming visual information from the retina in the form of action potential to several regions in the thalamus, hypothalamus, and mesencephalon. RGCs vary significantly in terms of their size, connections, and responses to visual stimulation but they all share the defining property of having a long axon that extends into the brain. These axons form the optic nerve, optic chaism, and optic tract.
Retinal prostheses, a type of bionic eye, are implantable electronic devices designed to stimulate sensation of vision in the eyes of individuals with significant retinal diseases such as retinitis pigmentosa or age-related macular degeneration, where the optic nerve and visual cortex are unaffected. restoration of vision may be achieved by creating devices, retinal prostheses, that receive and process incoming light and then transmit the information in the form of electrical impulses to the remaining inner retinal layers for visual function. Although visual prostheses may conceivably be developed for any part of the visual pathway including the visual cortex itself, the retina is considered to be the easiest target for treating outer retinal disease due to its easy access and partially intact geospatial neuronal architecture and processing units. Designs for retinal prostheses are generally categorized based on where in the eye the device is intended to be placed and how the device delivers electrical impulses to RGCs.
Retinitis pigmentosa (RP) is a genetic disorder of the eyes that causes loss of vision. It is estimated to affect 1 in 4,000 people and is generally inherited from a person’s parents. Symptoms include trouble seeing at night and decreased peripheral vision. Onset of symptoms is generally gradual and often in childhood. The underlying mechanism involves the progressive loss of rod photoreceptor cells in the back of the eye which is generally followed by loss of cone photoreceptor cells. There is currently no cure for RP.
The secondary visual cortex, also known as V2, or prestriate cortex, is the second major area in the visual cortex, and the first region within the visual association area. It receives strong feedforward connections from V1 and sends strong connections to V3, V4, and V5.
Subretinal implants sit on the outer surface of the retina, between the photoreceptor layer and the retinal pigment epithelium, directly stimulating retinal cells and relying on the normal processing of the inner and middle retinal layers. Adhering a sub retinal implant in place is relatively simple, and consists of a silicon wafer containing light sensitive microphotodiodes, which generate signals directly from the incoming light.
Suprachoroidal implants are placed between the posterior blood supply of the eye (choroid) and the outer white layer of the eye (sclera), with this surgical location primarily being chosen for stability and safety
Total blindness describes individuals with eye disorders who have no light perception. That is, a person who’s totally blind doesn’t see any light at all. Total blindness can be the result of trauma, injury, or various conditions.
Visual acuity is a measurement determined by the letter chart tests we take when we get our eyes checked; the number represents your eyes’ clarity or sharpness. For example, a person with a visual acuity measurement of 20/70 who is 20 feet away from an eye chart sees what a person with 20/20 vision can see from 70 feet away.
The entire area that can be seen when viewing a single point. Visual field tests are used to determine how a disease has affected loss of vision.