Retinitis Pigments - Essay Example

? Retinitis Pigmentosa Information Booklet Outline - Background and Etiology - Implications for functional vision - Functional and clinical visual assessments - What parents can expect Background and Etiology The retina is a membrane lining the inner circular surface of the eye. It is the most critical tissue in the eye that is necessary for vision, and cannot be repaired or replaced if damaged. The retina is made up of cells – called photoreceptors - that perceive light and generate nervous impulses that are transmitted to the brain. The pattern of activation of the photoreceptors in the eye depends on the image being viewed, as different receptors detect different colors of light. The brain contains a map of the visual field and interprets the pattern of retinal cell impulses that it receives to create an image, allowing the individual to ‘see’. There are two main types of photoreceptors: rods, which maintain visual acuity, and cones, which detect red, green or blue light. The term ‘retinitis’ denotes inflammation in the retina. Retinitis pigmentosa (RP) is a disease where the rod and/or cone cells of the retina slowly degenerate, progressively decreasing the quality of vision of the patient. The retina eventually develops a pigmented appearance, hence the name ‘pigmentosa’. ‘Retinitis’ is a slight misnomer for the disease, as there is no true inflammation taking place. It is a genetically inherited disease, meaning that it occurs due to the presence of defective genes. These genes code for proteins that are important for rods and cones. In the absence of these proteins, the rod and cone cells are unable to function for their full lifetime, and die over two to four decades. There are many different gene mutations that can lead to RP, and even the same mutation can produce differing severity or nature of disease in different patients. At least 40 different genes in humans have been identified that can have molecular defects to produce RP. About 20% of these are autosomal dominant, meaning that a person with the disease will always pass it on to his/her child. However, 50% of patients with RP do not have any relatives with the disease – these cases comprise of new mutations that occurred during gamete formation or conception. Implications for Functional Vision RP can be first noticed in infancy in some cases, or in the 50s in others. It is usually diagnosed in young adulthood. Its prevalence is 1 in 4000 in the United States. Patients initially complain of peripheral vision loss and poor vision at night. They may report bumping into furniture, and inability to see the ball out of the corner of their eyes in sports such as football. This can progress to increase the severity of visual impairment over several years or decades. There may be an eventual loss of central vision in some patients, leading to difficulties with small fine tasks. Complete blindness is rare in RP, and occurs in 0.5% of RP patients. Most patients do, however, have some degree of poor vision. Some cases of RP occur in patients with another ongoing disease, such as hearing loss, kidney disease, etc. Functional and Clinical Visual Assessments For a visually impaired child, a functional visual assessment helps determine the extent to which the child is using his vision to perform routine everyday tasks. This assessment can guide parents and teachers on which visual skills to develop further in order to optimize the child’s learning, and is important because vision affects 80-90% of what a child learns in the first five or six years of life. It is carried out by a teacher for the visually impaired, who is trained and certified. The assessment is carried out wherever the child is used to staying and is comfortable, including the home, school or community centre. The child is given simple everyday tasks, and his/her behavior and ability to complete the tasks are observed. Examples of aspects of vision that are observed in the child’s behaviour include: whether the child can clearly see near objects (at 16 inches) and far objects (at 10 feet); whether the child can fixate and maintain gaze on an object; whether the child can see an object out of the corner of his/her vision; whether the child can perceive different colors; and whether the child uses both eyes equally or one more than the other. If the child is unable to complete a task, implying a potential problem due to poor vision, the child’s environment is altered and the assessment is repeated, to find a way to help the child complete the task. For example, the lights in the environment may be increased, the objects may be brought closer, a larger object may be used, or the child may be given more time to complete the task. Thus, the environment that enables the child to use his vision best and complete most, if not all, tasks is identified. This information is used by the teacher to determine what methods and surroundings to use to help the child use his vision for learning and development as best as possible. The assessment can also include the child’s medical history, the medications list, and an interview of the child’s caregivers, to find out how the child usually grasps toys and other objects, how the child moves from indoors to outdoors, etc. This gives a clearer picture on how the child uses his vision during the day. If the child has not yet learned to read, or appears to be unable to see near or small objects clearly enough – in medical terms, has decreased visual acuity - several additional tests can be carried out to determine the severity of the child’s visual impairment. For example, in the ‘Stycar’ test, a set of balls are placed at increasing distances from the child. The child’s ability to see a distant object clearly is determined by the smallest ball the child can see at the furthest distance. Another specific investigation carried out to diagnose retinitis pigmentosa and rule out other causes of visual loss include the electroretinogram, which detects the strength of rod and cone signals generated in response to light. What parents can expect Raising a child with retinitis pigmentosa presents many challenges, and the prospect overwhelms quite a few. However, the medical community has gone to great lengths to devise management strategies to improve the quality of life of these patients so they can enjoy as normal a life as possible, and help is available for patients and caretakers every step of the way. Treatment for RP is currently limited, and no medications are yet available that can prevent, halt or reverse the visual impairment. Progressive loss of vision is inevitable, leaving most patients with eventual ‘tunnel vision’ where only the centre of the visual field is visible to patients. A small proportion of patients eventually become ‘legally blind’. Parents of a child with RP should consider seeing a genetic counselor to understand the likelihood of their future child, if any, of developing retinitis pigmentosa. There are specialized low-vision clinics available that deal with RP patients. The experts at these clinics evaluate patients with visual impairment and offer support, advice and prescribe the most effective treatments available. Current management strategies for RP patients include night-vision devices, magnifying devices and field-expanding lenses. These visual aids allow patients to maximize the use of their remaining vision. Patients may also be given injections and medications that have shown doubtful success in halting the progression of RP, with the hope of bringing possible benefit. These medications include Vitamin A, docosahexaenoic acid, calcium channel blockers, and a number of others. Most patients will require at least annual eye checkups to monitor progress of the disease. With continued research, it is possible that gene-targeted therapies may be developed in the future to halt the progression of RP in patients, help them preserve the rest of their vision, and/or reverse the visual loss. Recent breakthroughs in research include using gene therapy – delivering the normal gene to the diseased retina cells through a DNA virus – to cause recovery of vision in dogs suffering from retinitis pigmentosa. Other treatments still under experimental investigation include retinal prostheses with transducing chips, and stem cell retinal transplants. Thus, there is hope of more effective treatment options for retinitis pigmentosa becoming available in the future. References Medscape (2012) Retinitis Pigmentosa. [online] Available at: http://emedicine.medscape.com/article/1227488-overview [Accessed: 17 Mar 2012]. The Colorado Department of Education (2009) Fact Sheet - Functional Vision Assessment. [pdf] Available at: http://www.cde.state.co.us/cdesped/download/pdf/dbFuncVisionAssmt.pdf [Accessed: 16 March 2012]. University of Pennysylvania (2012) Gene therapy cures retinitis pigmentosa in dogs. ScienceDaily, [online] January 23rd. Available at: http://www.sciencedaily.com/releases/2012/01/120123152508.htm [Accessed: March 16, 2012]. Read More