David Zacks, a retina specialist and assistant professor of ophthalmology and visual sciences at the University of Michigan Kellogg Eye Center, explains.
Many of us think that as we grow older our eyesight is destined to deteriorate. We talk about "tired" or "old" eyes as if we are fated to have the gift of vision taken from us simply because we have aged. For example, in what might be the earliest reference to cataracts in the Bible (Genesis, Chapter 27, Verse 1) we learn that, "And it came to pass, that Isaac was old, and his eyes were dim..." The truth is that, with today's treatment options, there is no intrinsic reason for our vision to worsen with time. In theory, we should be able to retain undiminished our capability to accept, process and experience visual sensory input.
But, as with most conventional wisdom, there is an element of truth to the notion that age-related processes can affect our eyesight. The good news is that identifying and treating these processes can often result in the preservation or restoration of excellent vision for an entire lifetime.
A good understanding of vision loss requires a brief foray into the basic structure of the eye. Although it might be considered a clich¿, it is still useful to compare the eye to a video camera. Thus, as light enters the eye--or the camera--it travels through four main structures. By understanding this basic eye anatomy we can begin to understand the ways in which the light signal can be degraded or distorted, resulting in poor vision.
The entry point for light is the cornea, the transparent tissue in the very front of the eye that functions as the window through which all light has to pass on its way to forming a visual perception. Next, the light signal encounters the lens, which focuses it finely on the third structure of the eye: the retina. The retina is analogous to the film in the back of the camera. It is on the retina that the light is converted into a neural signal that is ultimately interpreted by the brain as an image. Finally, the optic nerve, which carries these signals to the brain, functions like a cable that connects the video camera to the television screen. The deterioration of our vision with age is invariably the result of a problem with one of these four structures.
The integrity of the corneal surface is very important for the reception of a clear image. If its surface is not smooth and intact the image will suffer, much like the image from a scratched camera. A very thin layer of tears coats the surface of the cornea. This tear surface, produced by various cells, some of which line the inner surface of the eyelid, is vital to maintaining the cornea¿s smooth surface and precise optical characteristics. Any condition that disrupts this tear film can lead to a breakdown of the cornea¿s surface and, thus, degradation of the image.
With age, this smooth surface can be damaged by conditions such as blepharitis, an inflammation of the eyelids. If the inflammation is severe enough, then the cells that produce the tears can be damaged, with an attendant impact on the tears coating the cornea. In this situation an individual may experience symptoms such as the sensation of a "film" over the eye, which is usually transient and relieved with blinking. More serious symptoms can also occur, such as blurry vision, which is due to evaporation of the tears and drying out of the corneal surface. This condition can become chronic and is known as dry eyes. Treatment options for blepharitis and dry eyes depend on the cause of the inflammation of the lid surface but can include warm compresses, artificial tears, oral antibiotics and even topical immunosuppressive agents to decrease the inflammatory response leading to the degraded tears.
The lens is also subject to the aging process, and the resulting conditions--cataracts and presbyopia--will eventually affect just about everyone. When we are born our lenses are crystal clear, meaning that the image entering the eye is not degraded by any opacity. They are also very pliable, meaning that the lens can change its shape to help focus images that are very far away as well as very close. Unfortunately, as we grow older two things happen to the lens: it clouds up and it becomes less pliable. The clouding of the lens--or cataract--forces an image to travel through a distorted medium, resulting in diminished vision. Similarly, when the lens loses its pliability it also loses its ability to focus over a wide range of distances. A hardened lens becomes more fixed on distant objects and cannot focus as well on nearby objects or vice versa. This hardening often occurs in middle age, when people notice the need to hold the newspaper farther away in order to read the print, and is known as presbyopia from the Greek words presbus, meaning old man, and opia, meaning eye.
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3 Comments
Add Commentwhy is there breakthrough for rp. i was told that ther will soon be a cure whats the update. pankg2001@gmail.com
Reply | Report Abuse | Link to thisi have son with rp .is thire any hope that he can be cured.
Reply | Report Abuse | Link to thisA friend just forwarded this to me. As we all know of a few important people who really need vision repair, this video is worth watching. The vets wounded in war should especially get this message. I just hope we don't have to go to Australia to get it. Follow-up definitely worth pursuing and passing on.
Reply | Report Abuse | Link to thishttp://gizmodo.com/5277456/stem-cell-contact-lenses-cure-blindness-in-less-than-a-month
Here's part of an article that names the involved people and institutions:
Stem cells used to restore sight for corneal disease sufferers
Leigh Dayton, Science writer | May 28, 2009
Article from:� The Australian
THREE Australians have had their sight restored thanks to their own stem cells and ordinary contact lenses.
Although the novel technique was used to reverse blinding corneal disease, it promises to be a quick, painless and cheap treatment for other visual disorders. It may even be useful for repairing damaged skin, the researchers reported today in the journal Transplantation.
The team leader, UNSW stem cell scientist Nick Di Girolamo said: We're quietly excited. We don't know yet if (the correction) will remain stable, but if it does it's a wonderful technique .
According to team member Stephanie Watson�- an opthalmic surgeon with Sydney's Prince of Wales Hospital�- two of the three patients were legally blind in the treated eye; they can now read big letters on the eye chart. The third could read the top few rows of the chart but is now able to pass the vision test for a driving license.