Transplantation Research

By Tom Hoglund

I wanted to expand on the discussion regarding transplant research. There are two types of retinal transplantation techniques; retinal cell rescue and photoreceptor cell transplants.

Retinal cell rescue transplants involve the implantation of cells that may rescue photoreceptor cells to slow the course of vision loss. Dr. Raymond Lund, The Foundation's Vice Chair for transplant research from the Institute of Ophthalmology in London, recently slowed the course of retinal degeneration in the RCS rat, an animal model of retinal degeneration, by transplanting Schwann cells from the rat's leg. Dr. Lund hypothesizes that the Schwann cells are able to produce various survival factors such as bFGF, CNTF and BDNF and is now testing this theory. These factors have slowed retinal degeneration in various animal models.

Autologous transplants such as the Schwann cell work by Dr. Lund may avoid some of the immune complications that occur with retinal pigment epithelium (RPE) transplants. The RPE is a cell layer beneath the neural retina that provides various survival factors and nutrients to the retina. In previous experiments supported by The Foundation, researchers have slowed vision loss in the RCS rat by transplanting RPE cells.

Transplanting cells genetically engineered to produce various survival factors is another evolving transplant method. Cytotherapeutics, a biotech company, slowed vision loss by implanting a encapsulated cell/drug delivery system. The device contained cells genetically engineered to produce CNTF, a survival factor that has been shown to slow the course of retinal degeneration in animal models.

It is interesting to note that this therapeutic modality results from advances in genetic, pharmaceutical and transplantation research. In second set of recent experiments, Dr. Lund performed photoreceptor cell transplants in the rd mouse, another animal model of retinal degeneration. The transplanted mice exhibited improved pupillary response when compared with control mice. This finding may provide the first evidence that transplanted photoreceptor cells can form nerve connections with the host retina to improve vision. However, further work is needed to verify these results.

Results from human photoreceptor experiments have thus far failed to show convincing evidence that vision improves. Clearly, there is a need to improve surgical techniques, to develop methods that promote nerve cell connectivity, and to identify the best age of dono r tissue. Pre and post-operative visual assessment must also be rigorous to insure results from future human experiments.

The Foundation's web page carries extensive coverage of transplant research. Click on the URL below to read these articles:

http://www.blindness.org/html/science/bretinal.html

Foundation for 
Fighting Blindness   http://www.blindness.org

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EYE DROPS ARE SERIOUS MEDICINE

By Post Eye Center

Because there are so many over-the-counter eye drops on the market, it's easy to forget that the ones prescribed by your doctor are often serious medications that should be treated like any other prescription medicine.

Although over-the-counter eye drops may look pretty much like the ones from your doctor, they are generally limited to moisturizers that soothe your eyes or "get the red out." Prescription drops, on the other hand, contain specific medicine intended for a specific purpose such as to combat infection or to control glaucoma.

By law, none of the non-prescription eye drops is a substitute for a prescription medication that your doctor wants you to use. The only substitute would be an exact generic equivalent recommended by your pharmacist.

Remember to treat eye drops prescribed by your doctor like any other prescription medicine. Follow the dosage directions and use the drops only for the purpose they were prescribed by your doctor.

Always remember: 

1.  Be sure you know the name of the medicine and how often to use it. 

2.  Pay attention to any warnings on the label. 

3.  If you have any uncomfortable symptoms, including an allergic reaction, call your doctor immediately. 

4.  Never use eye drops prescribed for another person. 

5.  Apply eye drops carefully in the following manner:

Pull the lower lid away from your eye with index finger.

Being careful not to touch the dropper to your lashes, lid, or eye, let one drop fall into the socket.

Close your eyes and do not blink for one minute so the drop can soak into your eyeball tissues.

Apply pressure to the inner corner of your eyelid to close the drain during the minute.

Use a clean tissue to wipe away excess drops on cheek.

Wait 5 minutes before any additional drops.

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Questions & Answers

Q. I have been told that the eyes of someone with RP are different from the eyes of someone who has Usher syndrome. What is the difference in the rate of visual loss for the two types of disorders?

A. Usher syndrome was described by Charles Usher, M.D., an ophthalmologiest from Scotland who studied visual impairments among families at institutions for the hearing impaired in Southern England and initially reported his findings in 1913. He noted two groups of families: in one the children were hearing impaired from birth, never learned to speak, and developed a retinal dystrophy similar to retinitis pigmentosa beginning between the ages of five and ten years; in a different set of families, children experienced hearing impairment of a milder degree, learned to speak, but developed pigmentary retinal dystrophy similar to retinitis pigmentosa roughly from age 10 to age 20. The techniques for analyzing Usher’s families have changed substantially since his original observations, since neither audiograms nor clinical electroretinograms were possible until the late 1940s. Nonetheless, we call those individuals with severe congenital hearing impairment who never speak (because they never hear) and develop a "retinitis pigmentosa"-like retinal dystrophy in the first decade of life Usher Syndrome Type 1. Usher Syndrome Type II refers to the milder form of retinal dystrophy associated with a milder form of congenital hearing impairment which is compatible with speech and conversation, but with a flat or nasal pattern. In each instance, as best as we can judge, the hearing impairment is stationary throughout life or only minimally progressive. The retinal disease in each type is progressive. When an ophthalmologist looks in the eye of a person with retinitis pigmentosa, the appearances can be remarkably similar. However, unless there is some other event occurring in the family, hearing impairment does not occur in typical retinitis pigmentosa, whereas in the Usher Syndromes, both hearing impairment and a progressive pigmentary retinopathy always occur together. (On the other hand, I have seen an occasional individual who inherited RP from one parent and a form of deafness from another parent, and thus had two independent and unrelated genetic diseases at the same time. Those individuals do not have Usher syndrome but rather have two diagnoses.) Both Usher Syndromes are always inherited as autosomal recessive traits.

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Q. Can a person have RP in one eye only?

A. By the usual medical definitions and conventions, retinitis pigmentosa is the descriptive name for a group of disorders, all of which are genetic (that is, caused by altered genes, and each of which may be transmitted differently in different families (dominant, recessive, X-linked, and no family history or "isolated." These disorders may number between 35 and 50, in the usual situations, we consider retinitis pigmentosa characterized by difficuly with dim light or night vision, progressive loss of peripheral or side vision, ultimate involvement of central or reading vision and associated with a characteristic process that involves the nerve tissue in the retina and the retinal pigment epithelium (which is the glue that bonds the retina to the inside lining of the eye.

Thus, retinitis pigmentosa is a single name for a group of disorders which are typically bilateral (both eyes involved), progressive (that is invariably get worse over time), and genetically determined. Scattered throough the ophthalmic and medical literature, there are occasional reports of individuals with "retinitis pigmentosa" in only one eye (sometimes called "unilateral retinitis pigmentosa.") Interestingly, these diagnoses are based typically on the characteristic appearances of pigment degeneration inside the eye, the loss of both central and peripheral vision in one eye, which does not occur in the other eye. Thus, something which looks remarkably similar to retinitis pigmentosa in some individuals and is described as a complication of trauma to the eye (such as a blunt injury), as following a complete retinal detachment with spontaneous retinal reattachment, as following certain infections or parasitic infiltrations of one eye only, and in many instances, unassociated with any other recognizable feature.

However, in no instance has unilateral retinitis pigmentosa ever occurred in a family, and in no instance has anyone with unilateral retinitis pigmentosa ever proceded to have a child with retinitis pigmentosa.

As such, it is assumed, by the best available medical information, that there is no truly genetic disorder called "unilaterial retinitis pigmentosa" nor does unilateral pigmentary degeneration which resembles RP replace the individual or the family at any higher risk or future generations than the expected risk in the general population. Occastionally, true retinitis pigmentosa can be slightly asymetrical between the two eyes and thus one might mistakenly think one one was relatively uninvolved. However, careful observation by a diligent observer will reveal most of the characteristics of RP, clarifying that indeed, this is a bilateral disease.

In summary, unilateral retinitis pigmentosa in the usual sense of our use of the term does not exist as a genetic disorder, but rather mimics RP, because of the appearance of the retinal degeneration caused by some other insult.

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Q. Is there a relationship between child-bearing and deterioration of vision?

A. Several historical anecdotes suggest that women who have Retinitis Pigmentosa and become pregnant experience an acceleration of their RP, that is, an increased rate of visual field loss or an accelerated loss of central vision. However, such claims are non-existent.

Furthermore, there is no experience to suggest that women creating artificial states of pregnancy, such as with birth control pills, fertility hormones, and so forth accelerate the rate of their Retinitis Pigmentosa.

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Q. I belong to a support group and two of my friends have lost more vision as a result of having unrelated surgery that required anesthesia. Is there a connection?

A. This question is unanswerable. One would need to know the nature of the visual impairment, the specific diagnosis of the type of retinal dystrophy, the visual status before the surgery, including visual acuity and visual field, the nature of the surgery, the nature of the anesthetic, and certain other factors including the duration of the procedures. In addition, the visual acuity after the surgery and other parameters would need to be accessed. There is no known relationship or risk to RP patients undergoing local or general anesthesia.