Quick RP Overview | Retinitis Pigmentosa Overview
Retinitis pigmentosa (RP) is a rare, hereditary disease that causes the rod photoreceptors in the retina to gradually degenerate. The rods are located in the periphery of the retina and are responsible for peripheral and night vision. Cones, another type of photoreceptor, are densely concentrated in the macula. The cones are responsible for central visual acuity and color vision.
The disease may be X-linked (passed from a mother to her son), autosomal recessive (genes required from both parents) or autosomal dominant (gene required from one parent) trait. Since it is often a sex-linked disease, retinitis pigmentosa affects males more than females.
People with RP usually first notice difficulty seeing in dim lighting and gradually lose peripheral vision. The course of RP varies. For some, the affect on vision may be mild. Others experience a progression of the disease that leads to blindness.
In many cases, RP is diagnosed during childhood when the symptoms begin to become apparent. However, depending on the progression of the disease, it may not be detected until later in life.
Signs and Symptoms
· Difficulty seeing dim lighting
· Tendency to trip easily or bump into objects when in poor lighting
· Gradual loss of peripheral vision
· Glare
· Loss of contrast sensitivity
· Eye fatigue (from straining to see)
Detection and Diagnosis
Retinitis pigmentosa is usually diagnosed before adulthood. It is often discovered when the patient complains of difficultly with night vision. The doctor diagnoses RP by examining the retina with an ophthalmoscope. The classic sign of RP is clumps of pigment in the peripheral retinal called “bone-spicules.” A test called electroretinography (ERG) may also be ordered to study the eye’s response to light stimuli. The test gives the doctor information about the function of the rods and cones in the retina.
Treatment
There is currently no standard treatment or therapy for retinitis pigmentosa; however, scientists have isolated several genes responsible for the disease. Once RP is discovered, patients and their families are encouraged to seek genetic counseling.
Current Research
Scientists at Johns Hopkins University are developing a micro-computer chip prosthesis called the Multiple-unit Artificial Retina Chipset (MARC). Once implanted in the retina, the chip transmits images to the brain that are captured from a small camera mounted on the patient’s glasses. The chip is still in development and is not yet available for widespread use.
Doctors continue to search for treatments for RP but have yet to find a cure.
St. Luke’s Cataract & Laser Institute provides this on-line information for educational and communication purposes only and it should not be construed as personal medical advice. Information published on this St. Luke’s website is not intended to replace, supplant, or augment a consultation with an eye care professional regarding the viewer/user’s own medical care. St. Luke’s disclaims any and all liability for injury or other damages that could result from use of the information obtained from this site.
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Retinitis Pigmentosa Definition
Written by Lazy1
Wikipedia’s definition of Retinitis Pigmentosa
Retinitis pigmentosa (RP) is a group of genetic eye conditions. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some sight all their life. Others go completely blind from RP, in some cases as early as childhood. Progression of RP is different in each case. RP is a type of hereditary retinal dystrophy, a group of inherited disorders in which abnormalities of the photoreceptors (rods and cones) or the retinal pigment epithelium (RPE) of the retina lead to progressive visual loss. Affected individuals first experience defective dark adaptation or nyctalopia (night blindness), followed by reduction of the peripheral visual field (known as tunnel vision) and, sometimes, loss of central vision late in the course of the disease
Related Health Topics:
Inheritance of Retinitis Pigmentosa
Written by Wiggy
To understand the mechanism and probabilities involved when considering starting or enlarging a farnily we must first look at some basic concepts of genetics. This article will explore three examples of inheritance of retinitis pigmentosa: Dominant; Recessive, and X-linked (or Sex-linked).
Massachusetts Eye and Ear lnfirmary
Electroretinography Service
Eliot L. Berson, Director
Some lnformation Concerning the lnheritance of
Dominant Retinitis Pigmentosa
When dominant retinitis pigmentosa appears in a family, any given member will either be
AFFECTED (that is, manifest the disease and able to pass it to their offspring); or
UNAFFECTED by retinitis pigmentosa (completely free of the disease, and unable to pass it to their offspring).
There are no carriers (those not manifesting the disease, but nevertheless able to
pass it to their offspring) in this form of inheritance.
To understand the mechanism and probabilities involved when considering starting
or enlarging a family in which this form of retinitis pigmentosa appears, we must first
look at some basic concepts of genetics.
The genetic code which determines every characteristic of our body is duplicated;
that is, there are two genetic components responsible for every trait. Normally, should
one of these components prove defective, the other (correct) component will override
the function of the defective one. The distinguishing feature of dominant inheritance
is that, should a trait be dominantly inherited the defective copy will prevail, resulting
in this case in dominant retinitis pigmentosa.
For an affected child to be produced in this form of retinitis pigmentosa one parent
must also be affected.
Each individual child of these parents will have a 5O % (2 in 4) chance of
inheriting the abnormal genetic component. They will manifest the disease
and be affected. They will also be capable of passing the defective genetic
material to their offspring.
Each individual child of these parents will have a 5O% (2 in 4) chance of not
inheriting the abnormal genetic component. They will be unaffected by retinitis
pigmentosa. They will neither manifest the disease nor be able to pass it to
their offspring.
Please Note: A common error in interpreting genetic mechanisms when they are
expressed in terms of percentages or fractions is to assume that if one has a first child
affected through dominant inheritance (in a situation reflecting a 50% or a 2 in 4 risk
factor), that the next son will not be endangered. THIS lS NOT TRUE! AII offspring of
the same father and mother run the same risk.
It is currently possible to ascertain whether an individual is a affected by this form of
retinitis pigmentosa with electroretinographic testing. We hope this brief introduction
to dominant inheritance will help you to understand this genetic pattern of retinitis
pigmentosa.
The Staff of the Electroretinography Serice.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Massachusetts Eye and Ear lnfirmary
Electroretinography Service
Eliot L. Berson, Director
Some lnformation Concerning the lnheritance of
Recessive Retinitis Pigmentosa
When recessive retinitis pigmentosa appears in a family, it frequently occurs that
both parents of an affected child have good vision and appear (ophthalmologically)
essentially normal. What is the explanation of this situation?
The genetic code which determines every characteristic of our body is duplicated;
that is, there are two genetic components responsible for every trait. lt sometimes
happens that one component will be normal while the second proves defective.
Normal genetic codes override the function of defective ones, so in this case the
individual will not exhibit any symptoms but will be a carrier of the trait, in this case,
retinitis pigmentosa.
Each individual child of these parents will have a 25% (1 in 4) chance of
inheriting two defective genes. They will manifest the disease and be
affected. They will also be capable of passing the defective genetic material
to their offspring.
Each individual child of these parents will have a 50% (2 in 4) chance of
inheriting one normal and one defective gene. They will become carriers of the
disease, like their parents. They will not manifest symptoms of the disease, but
will be able to pass the defective genetic maierial to their offspring.
Each individual child of these parents will have a 25% (1 in 4) chance of
inheriting two normal genes. They will be unaffected by retinitis pigmentosa.
They will neither manifest the symptoms of the disease nor be able to pass it
to their offspring through their genetic material.
Please Note: A common error in interpreting genetic mechanisms when they are
expressed in terms of percentages or fractions is to assume that if one has a first child
affected through recessive inheritance (in a situation reflecting a 25%, or a 1 in 4 risk
factor), that the next son will not be endangered. THIS lS NOT TRUE! All offspring of
the same father and mother run the same risk.
We estimate that 1 out of 80 people in this country are carriers of recessive retinitis
pigmentosa.
The chance that an affected patient will marry a carrier is about 1 in 80;
The chance that a carrier will pass on the genetic defect is 1 in 2;
Therefore, the chance that an affected patient will have an affected child is about 1 in
80 times 1 in 2, or 1 in 160 for each individual chitdbirth.
All offspring of an atfected patient will be carriers. The situation when these
carrier offspring come to marry will be the same as that described at the beginning:
The chance that a carrier offspring will marry a carrier is about 1 in 80;
The chance that these carrier parents will produce an affected child is
1 in 4 for each individual childbirth;
Therefore, the chance that an unaffected, carrier offspring will have an affected child
is about 1 in 80 times 1 in 4, or 1 in 320 for each individual childbirth.
No test is available at present to detect carriers of this form of retinitis pigmentosa.
We hope this brief introduction to recessive inheritance will help you to understand
this genetic pattern of retinitis pigmentosa.
The Staff of the Electroretinography Service.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Massachusetts Eye and Ear lnfirmary
Electroretinography Service
Eliot L. Berson, Director
Some lnformation Concerning the lnheritance of
X-Linked (or Sex-Linked) Retinitis Pigmentosa
When X-linked retinitis pigmentosa (or RP) appears in a family, any given member will be
AFFECTED (that is, manifest the disease and able to pass it to
their offspring); a
CARRIER (those who, while not manifesting the disease are
nonetheless able to pass it to their offspring); or
UNAFFECTED as regards retinitis pigmentosa (completely free
of the disease, and unable to pass it to their offspring).
To understand the mechanism and probabilities involved when considering starting
or enlarging a farnily in which this form of retinitis pigmentosa appears, we must first
look at some basic concepts of genetics.
The genetic code which controls each characteristic of our body is governed by
forty-six chromosomes, which we receive from our parents- half from our mother and
half from our father. Of these forty-six chromosomes, forty-four are (ideally) identical,
whether they come from the father or the mother. But two chromosomes are special-
they contain the genetic coding for all sexual differentiation. There are two types of
these special chromosomes, referred to as Xs or Ys on account of their shapes.
Females always have two Xs, but males have one X and one Y. A mother can only
contribute an X chromosome to her child. Daughters are produced when each parent
passes on an X chromosome. Sons are produced when the father passes on his
Y chromosome, rather than his X. For every birth, therefore, the probability of
producing a son or a daughter is exactly equal- 50%. The deciding factor is which of
the father’s sexual chromosomes is passed on, the X or the Y.
The defective genetic code which results in this form of retinitis pigmentosa is
always found on the X chromosome. This is why this type of the disease is sometimes
referred to as “X-linked”. Because these X chromosomes are responsible for
gender, a disease resulting from their faulty genetic coding will occur in a way directly
related to gender. This is why the same type of retinitis pigmentosa is sometimes
referred to as “sex-linked”.
lf the mother is a Carrier and the father (as regards retinitis pigmentosa) is Normal:
Each individual son of these parents wili have a 5O% (2 in 4) chance of
inheriting the defective X chromosome. They will manifest the disease and
be affected. They will also be capable of passing the defective genetic
material to their daughters.
Each individual son of these parents will have a 50% (2 in 4) chance of
inheriting two normal chromosomes. They will be unaffected by retinitis
pigmentosa. They will neither manifest the symptoms of the disease nor be
able to pass it to their offspring through their genetic material.
Each individual daughter of these parents will have a 50% (2 in 4) chance
of inheriting one normal and one defective chromosome. They will become
carriers of the disease, like their mother. They will not manifest symptoms of
the disease, but will be able to pass the defective genetic material to their
offspring.
Each individual daughter of these parents will have a 50%” (2 in 4) chance
of inheriting two normal chromosomes. They will be unaffected by retinitis
pigmentosa. They will neither manifest the symptoms of the disease nor be
able to pass it to their otfspring through their genetic material.
lf the mother is Unaffected and the father is Affected by retinitis pigmentosa:
Each and Every Son of these parents will inherit two normal chromosomes.
They will be unaffected by retinitis pigmentosa. They will neither manifest
the symptoms of the disease nor be able to pass it to their offspring through
their genetic rnaterial.
Each and Every Daughter of these parents will be a carrier of the disease.
They will not manifest symptoms of the disease, but will be able to pass the
defective genetic material to their offspring.
Please Note: A common error in interpreting genetic mechanisms when they are
expressed in terms of percentages or fractions is to assume that if one has a first son
affected through sex-linked inheritance (in a situation reflecting a 50% or a 2 in 4 risk
factor), that the next son will not be endangered. THIS lS NOT TRUE! All offspring of
the same father and mother run the same risk.
It is currently possible to ascertain whether an individual is a carrier of this form of
retinitis pigmentosa to a 96% degree of certainty through electroretinographic testing.
We hope this brief introduction to sex-linked inheritance will help you to understand
this genetic pattern of retinitis pigmentosa.
The Staff of the Electroretinography Seruice.
Lasik
Why Choose Marmer Medical Eye Center?
Robert H. Marmer, M.D. has the longest experience performing refractive surgery in the state of Georgia by introducing the first refractive surgical procedure in 1979.
We can serve as your resource for information on LASIK and related procedures. Please call today for your evaluation. Remember, our excellence is from experience
Are You A Candidate for LASIK?
The ideal candidate for LASIK is over 18 years old with normal health and a prescription that has not increased significantly in the last 12 months. People with certain medical conditions or women who are pregnant may not be good candidates for LASIK.
What kind of results can I expect?
Depending on your prescription and how quickly you heal, you may experience the results of LASIK immediately. Most MMEC patients are capable of reading the clock in the laser room moments after their procedure, and usually demonstrate legal driving vision the next day. You can expect your vision to continue to improve over the next few days or weeks, as Dr. Marmer monitors your progress at your regularly scheduled appointments.
For most patients, laser vision correction permanently reshapes the cornea, resulting in excellent vision even many years later. A small percentage of patients treated have required a repeat treatment, or “LASIK enhancement”.
What does the cost of the procedure include?
Your fee covers your LASIK consultation, the pre-operative evaluation, your surgery, all facility fees, medications and a full year of post-operative care. The fee also includes the Lifetime Assurance Plan, which provides LASIK enhancements, if needed, at no additional fee from Dr. Marmer.
Following surgery, Dr. Marmer will closely monitor your progress for a full year. After your year of free follow-up care, you need to be seen on an annual basis in order to maintain eligibility for the Lifetime Assurance Plan.
Is LASIK covered by my insurance plan?
Insurance rarely covers elective procedures like LASIK.
Are there any ways to make LASIK more affordable?
Marmer Medical Eye Center can assist you in obtaining financing through one of several sources, with low monthly payments.
If you have a Medical Flex-Spending Account through your employer, you can use pre-tax earnings to reduce your effective cost by hundred of dollars.
Of course, you also have the option of extending your payment period by using most major credit cards.
Will the procedure hurt?
Anesthetic drops prior to surgery help to numb the surface of the eye, minimizing the chances of discomfort during the procedure. You may experience a dry, scratchy sensation immediately after surgery, but most patients are quite comfortable after taking a short nap. Any mild discomfort after surgery should respond well to the eye lubricant drops provided in your free post-op kit.
Are there any risks?
Yes, but less than 1% of LASIK patients develop complications that can reduce the quality of their corrected vision. Dr. Marmer will attempt to minimize the risk of problems by carefully evaluating your overall eye health and candidacy for LASIK. The appropriate risks, benefits and expectations specific to your case will be addressed at your pre-operative exam and again before you go into surgery.
Does Marmer Medical Eye Center stand behind my results?
Absolutely! MMEC stands behind the results of LASIK Surgery. While we cannot guarantee that you will have perfect distance vision for a lifetime, our Lifetime Assurance Plan is designed to help you maintain excellent vision forever. Most nearsighted patients qualify for the plan, provided they have no significant health problem and are not outside the acceptable prescription range. It is possible that LASIK enhancement may not be the best option. This will be determined after careful evaluation.
What will my recovery be like?
Most LASIK patients are very excited about the quality of their vision the day after their procedure, typically arriving for their one-day visit with legal driving visions! While most patients notice dramatic visual results within the first few days following their procedure, the speed of visual recovery depends on personal healing patterns and the amount of treatment provided. Patients with extremely high prescriptions, for instance, often recover more slowly, but tend to be some of our happiest patients.
How do I get to the Laser Eye Center for the LASIK procedure?
Dr. Marmer performs all LASIK procedures at the TLC Atlanta Laser Eye Center. It is loccated at 4505 Ashford-Dunwoody Rd. NE, Atlanta, GA 30346. Click here for detailed directions.
Hemianopic Patients
Visual rehabilitation therapy widens horizons for patients with visual field loss, proponents say.
How it Works
Launched in the United States in 2003 by NovaVision, VRT is a home-based treatment program designed to expand the visual field of hemianopic patients by stimulating the border zone between the blind and seeing fields, facilitating neuroplasticity. Patients work on a leased VRT device twice each day for approximately 30 minutes per session, 6 days a week. The VRT requires them to fixate their vision on a central point while it stimulates the brain’s visual repair mechanisms, according to the manufacturer. The course of treatment lasts 6 months. The therapy is regularly monitored by the physician, who may recommend further treatment is he or she deems it appropriate.
Dr. Marmer warns that little improvement typically occurs during the first month, so the physician should make an effort to keep patients motivated.
Recent data presented at the American Academy of Neurology 61st Annual Meeting showed functional improvement in reading and trail-making for 39 patients with a homonymous visual field defect who had performed at least 6 months of VRT. Reading speed improved by 21.6% and stimulus detection during visual field testing increased by 10.4%.
Hemianopic Patients
NovaVision’s Vision Rehabilitation Therapy. For more information, go to the company’s Web site at www.novavision.com.
A functional magnetic resonance imaging study performed by researchers at Columbia University Medical Center on six chronic right hemianopic patients shows that by performing VRT the patients had an increase in brain activity.2
Patients recover an average of 5% of visual field, reports NovaVision.
Real Life Results
The regimen of “visual workouts” pays off, according to Dr. Marmer, increasing patients’ ability to function in everyday life. They are able to avoid collisions with objects in their environments and read more easily and more quickly.
“We take for granted that you read from left to right, then go back to the left of the next line and start again,” explains Dr. Marmer. But patients with a field defect, particularly on the left, can’t find the beginning of the next line. “So VRT not only helps patients get around without bumping into things, it helps them with reading and anything that requires better visual function,” Dr. Marmer says. “It’s a significant tool to be able to have in your treatment ability, when I couldn’t offer them anything before.”
One of the most exciting things about VRT, Dr. Marmer says, is that the success of the therapy is not time-sensitive relative to the date of injury. “If you had your stroke 3 years ago, or 10 years ago, it’s not too late. Both types of patients seem to get a similar ability to improve,” he says.
Raising Questions
VRT has only recently been launched in ophthalmology, however, and some are skeptical about how much it can do for patients who have lost visual field. Victoria Pelak, M.D., associate professor of Neurology and Ophthalmology at the University of Colorado Denver School of Medicine, does not prescribe the therapy to her patients, though she did examine one patient who had undergone it prior to coming to her. Dr. Pelak reports that the patient believed the therapy had been helpful. Still, she wonders if the benefit might come from a practice effect.
Patients “may show improvement because they have had persistent practice with that manner of testing,” Dr. Pelak explains. “There are eye movements that patients can make that allow them to see areas that they weren’t able initially to see in.”
Eli Peli, M.Sc., O.D., a senior scientist at Schepens Eye Research Institute, professor of ophthalmology at Harvard Medical School, and developer of peripheral prism eyeglasses for hemianopic patients, also has reservations. “Patients get 5 degrees [of visual field expansion] on average, and those with more visual field loss get less, or the patients that have less loss get more,” says Dr. Peli, who has not used VRT. Unfortunately, that means those patients most in need of help will fare worse than milder cases. He also expresses the opinion that 5 degrees of visual field gain “isn’t much — about four fingers at arm’s length.”
Answering the Skeptics
After seeing VRT improve the lives of about a half dozen patients who have undergone the therapy, however, Dr. Marmer disagrees with critics. His career-long interest in retinitis pigmentosa helped him to understand how even a small improvement in visual field could improve a patient’s visual function.
“For someone who has a full visual field, it’s hard to believe that just a tiny bit of improvement is going to make that much more difference,” he says. “Just 5 degrees of improvement is a minimal amount in the overall picture. But for these people, it really is huge. It is a major change in their ability to function. And these patients are generally elderly, so any small improvement is a great help to them.” Even that 5 degrees, Dr. Marmer says, can give patients enough function that they don’t need someone to assist them all the time.
As for the “practice effect” theory, Dr. Marmer points out the NovaVision was able to document increased cortical activity with functional MRI scans.
Yet he says VRT does have its limitations in that visual field improvement cannot be pushed beyond a certain threshold. “Suppose the patient has worked 30 minutes a session, twice a day for 6 days and now have 5 degrees more visual field. Now there’s a whole new border zone, as they call it, between the blind field and the seeing field. Could we refocus our stimulation to that spot and work for another 30 minutes, twice a day, 6 days a week, for another 6 months and get an additional 5 degrees — and keep doing this until you get back your full visual field again? I wish we could do that, but there is eventually a limitation that the brain can’t recover from.”
Patient Selection Tips
Dr. Marmer also cautions that certain patients are not good candidates for VRT. Patients need at least 20/200 vision to participate, as well as mental alertness and the ability to focus for approximately 30 minutes per session.
Additionally, “If they can’t fixate their vision at the very central point, if they have abnormal or uncontrollable eye movement that doesn’t permit them to fixate on one fine point of light, for example, then the treatment may not be successful because they cannot allow the stimulation to the areas that are necessary,” says Dr. Marmer.
A form of epilepsy that is triggered by flashing lights is also a contraindication.
But while there are subsets of visual field loss patients whom VRT cannot help, Dr. Marmer points out that there are many more for whom the therapy is valuable. “It’s a significant tool to have in my treatment arsenal. Before, I couldn’t offer them anything.” OM
Reference
1. Schlueter D, Schulz P, Kenkel S., Romano JG. Functional Improvement after a Visual Rehabilitation Intervention for Patients with Homonymous Visual Field Defects. Presented at: American Academy of Neurology 61st Annual Meeting, Seattle, Apr. 28, 2009.
2. Marshall RS, Ferrera JJ, Barnes A, Zang X, O’Brien KA, Chmayssani M, Hirsch J, Lazar RM. Brain Activity Associated With Stimulation Therapy Of The Visual Border Zone In Hemianopic Stroke Patients. Neuro Rehabilitation Neural Repair. 2008 2, Epub 2007 Aug 14.
