Retina
The retina is very thin layer of tissue that kines the inner part of the eye. It is responsible for capturing light rays that enter the eye much like a camera film's role in photography. These light impulses are then sent to the brain for processing, via the optic nerve.
Fifty percent of all blindness is caused by damage to the retina, diabetic retinopathy being one of the major culprits. Almost 10 million people world-wide are blind as a result of Age-related Macular Degeneration (AMD) and Retinitis Pigmentosa (RP).

What is Retinitis Pigmentosa?
Retinitis pigmentosa (RP) is the name given to a group of inherited eye diseases that affect the retina. RP causes the degeneration of photoreceptor cells in the retina. Photoreceptor cells capture and process light helping us to see. As these cells degenerate and die, patients experience progressive vision loss RP symptoms can vary. In a person with classic or typical RP, night vision and peripheral (or side) vision will be affected initially. Night blindness is one of the earliest and most frequent symptoms o RP. The loss of peripheral vision is often called tunnel vision. If you imagine peering down a tunnel, able only to see what is in front of you and nothing to the side, this is what it is like to lose peripheral vision. As vision loss progresses, the tunnel becomes more and more narrow. In the later stages some patients may also lose central vision. What is common to all cases of RP is the progressive nature of the disease.

Not much is known about the cause of retinitis pigmentosa, except that it is inherited. If neither of your parents have retinitis pigmentosa, at least one of them must be a carrier.

http://www.jwen.com/rp/faq/rpfaq.html

What is Age-related Macular Degeneration (AMD)?
AMD is a common eye disease associated with aging that gradually destroys sharp, central vision, Central vision is needed for seeing objects clearly and for common daily tasks such as reading and driving. In some people, AMD advances so slowly that it will have little effect on their vision as they age. But in orders, the disease [progresses faster and may lead to a loss of vision in one or both eyes. (www.amd.org)

In Retinitis Pigmentosa & AMD, patients are visually impaired due to loss of photoreceptors, the light-sesing cells of the eye.
Researchers are trying to develop a silicon microchip which will replace the photoreceptor layer of the retina and act as an artificial retina.

The tiny self-contained chip, slightly larger than the head of a pin, is surgically implanted on the retina at the back of the eye. The chip contains microscopic solar cells that are designed to convert light energy into thousands of electrical impulses.
These signals would then stimulate the intact, functional cells of the retina in patients with photoreceptor cell damage. This stimulation induces biological visual signals in the good retinal tissue. The nerve fiber layer of the retina can then do its job of sending these electrical signals to the brain, via the optic nerve.
Researchers are currently working on two models depending on the layer of the retina that this implant will be placed upon. The implant can either be placed on the surface of the retina as shown in the figure on the left or within the retinal layers as shown in the figure on the right.

Researchers from all over the world are making attempts to fabricate such a device. Some such groups have already tested the clip in human trials and reported improved vision. The only eye centre in India to venture into this highly tough and competitive field is Aditya Jyot Eye Hospital Pvt. Ltd. It has been the Chairman and Medical Director, Dr. S Natarajan's dream project. He has been dwelling on this problem for half a decade now. Aditya Jyot has already made some progress by taking the first and significant step of contacting the right agencies which could help develop such an electronic device.
Feasibility studies are presently on.

Stem Cell Research

Limbal Stem Cells
The eye's cornea is the clear tissue that allows light to enter the eye. It also refracts light rays to focus onto the retina Between the cornea and the sclera, the eyeball's white outer coating, is the limbus, where some very important cells reside. Limbal stem cells are mother cells the give rise to the corneal epithelial cells. Severe damage to limbal stem cell significantly impairs a person's vision.
To treat cases of limbal stem cell deficiency, the limbal stem cells are taken from the healthy eye or donor eye and then transplanted to the affected eye. If the transplant is successful the limbal stem cells will produce a new layer of epithelial cells in the patient's eye. The success rate of growing cells in the patient's eye. The success rate of growing the new cells from transplanted limbal stem cell varies

To treat cases of limbal stem cell deficiency, the limbal stem cells are taken from the healthy eye or donor eye and then transplanted to the affected eye. If the transplant is successful the limbal stem cells will produce a new layer of epithelial cells in the patient's eye. The success rate of growing cells in the patient's eye. The success rate of growing the new cells from transplanted limbal stem cell varies from 25%percent to 70 percent, depending on the underlying condition of the eye. The image illustrates limbal cells being taken from the donor eye. An emerging approach uses a fraction of the amount of limbal stem cells normally taken from a live donor, grow the in the laboratory and then transplants the same into the affected eye. In some cases, a limbal stem cell transplant alone can make a patient's vision considerably better. For other patients, the limbal stem cell transplant sets the stage for what follows - a cornea transplant. Aditya Jyot is in final stages of tying up with a biomedical agency to conduct clinical trials using such autografts.