Retinitis pigmentosa is the term used for a number of genetic disorders affecting the retina. The disease is progressive inevitably leading to blindness. The majority of patients are confirmed legally blind before they enter their 50s or even 40s. In severe forms of the disease loss of vision occurs during childhood.
Initially, damage to vision is in the form of night blindness. After that the person develops so called tunnel vision characterized by a loss of peripheral vision with retention of central vision and in the end vision loss completely takes place.
It is estimated that approximately 100,000 people in the United States have retinitis pigmentosa. Transmission of the defective genes may be achieved through autosomal dominant inheritance, autosomal recessive inheritance and X-linked inheritance. The defective genes are blamed for production of some non-functional proteins or retinal cells synthesize adequate proteins but not in optimal amounts.
Symptoms and Signs of Retinitis Pigmentosa
Symptoms of retinitis pigmentosa vary according to whether the damage affects first rod or cones. In the majority of cases rod cells of the retina are involved first. These cells are in charge of night vision. Their damage, therefore, leads to problems with night vision and may be additionally blamed for problems with peripheral vision. Further progression of the disease affects the cone cells of the retina. These cells play major role in color vision and are predominantly located in the center of the retina being responsible for central vision. Their damage is clearly a reason why patients start to experience issues regarding color vision and finally lose vision for good (both peripheral and central). If damage affects the cone cells forts, loss of central vision and inability to differentiate colors are the first two things patients complain about.
All patients undergo thorough examination and several eye tests. Patient's medical history, family history and the very symptoms he/she complains about are of great help when it comes to diagnosing retinitis pigmentosa.
An ophthalmologist will perform a number of eye tests and evaluate the retina. These include color vision, a complete retinal exam, fluorescein angiography, refraction test, retinal photography and he/she also measures intraocular pressure, the electrical activity in the retina and checks pupil reflex response. Side vision test, slit lamp examination and visual acuity test are performed as well.
The inheritance pattern is determined by family history. It is estimated that at least 35 different defective genes may be involved in the process of damage to the retina. Many times retinitis pigmentosa is first diagnosed in adolescence. The progression varies and is individual. The most severe cases are the ones inherited in X-linked fashion. This can be easily explained. Namely, men have only one X chromosome and women two. So, in women the other chromosome can be normal and they are then classified as carriers. Men, having only a single X chromosome are always affected by the disease. The disease may also occur in women but they need to inherit both defective X chromosomes.
Apart from occurring alone retinitis pigmentosa may be a characteristic of certain syndromes. For instance, it is together with hearing loss a part of Usher syndrome. Furthermore, a condition called Kearns-Sayer syndrome is characterized by retinitis pigmentosa and ophtalmoplegia, dysphagia, ataxia and problems regarding the heart conduction system. Abetalipoproteinemia, neurosyphilis and toxoplasmosis are a few more conditions associated with this genetic disorder.
If one family member is confirmed to suffer from retinitis pigmentosa, other members must be examined for the symptoms and signs of the condition too.
Retinitis pigmentosa is, unfortunately, incurable. However, the progression of the disease may be somehow decelerated with a daily intake of 15000 IU of vitamin A palmitate. Vitamin A is essential for retinal cells. According to available data supplements containing the vitamin may delay the onset of blindness by 10 years maximum.
Since this is a genetic condition, there is no available treatment that can repair damaged genes. Still, scientists are exploring various treatments which may perhaps bring the progression of retinitis pigmentosa under control and prevent rapid loss of vision.
Medical experts hope that one day these patients will be cured with retinal transplants, artificial retinal implants or gene therapy. There are many ongoing studies including stem cells and nutritional supplements. Patients are also treated with certain drugs that may be efficient against retinal damage.
One of the most significant discoveries was made in UK in 2006. The research included transplantation of mouse stem cells into mice that were suffering from retinitis pigmentosa and age-related macular degeneration. These stem cells were prepared in such a way that they were ready to develop into photoreceptor cells. The stem cells successfully turned into photoreceptors and managed to connect with retinal nerve cells. The formation of photoreceptors along with formation of connections with the rest of the retina is of vital importance for vision restoration. The results of the research are rather encouraging, giving hope that in future similar effect will be achieved in humans.