Retinitis Pigmentosa  & Blindness


While macular degeneration affects the acuity of a person’s vision, retinitis pigmentosa (RP) is largely associated with loss of peripheral sight, or the field of vision, in its first stages. Visual acuity and even colour vision may be affected later in the course of the retina’s degeneration, however, and there are certain types of RP which affect the macula and thus the acuity of the eye’s vision.

What is Retinitis Pigmentosa (RP)?

Retinitis pigmentosa designates a group of diseases which affect a portion of the retina known as the pigment epithelium.  The pigment epithelium is one of two layers found within the retina and has millions of photoreceptor cells, or rods and cones.  This layer consists mainly of rods which control the peripheral vision while the other layer, or neural retina, contains the macula which is the centre of the eye full of cone cells making this the thicker of the two cell layers. This is a relatively rare disease afflicting only about one in 3-4,000 people.

How does Retinitis Pigmentosa (RP) affect the eyes?

Retinitis pigmentosa, as the name suggests, affects the pigment epithelium and its rods which control peripheral and basic visual functions. RP materialises from a genetic defect in the eye which causes the photoreceptor cells to breakdown. Because the first thing it damages are the rod cells of the pigment epithelium, first symptoms include nyctalopia or loss of night vision, tunnel vision due to loss of peripheral sight, or photopsiae which is the seeing of flecks, flashes of light, or sparkles in the vision.

As the retina continues to be affected, the macula portion of the eye may be harmed as well. This is generally in the last stage of RP. The retina is a layer of cells lining the blood vessels of the eyeball. When the retina has been sufficiently compromised, the vessels may leak into the eye, a process called exudation.  This leakage can damage the cone cells clustered in the macula, leading to central vision loss in addition to the peripheral loss from early stages. Because the cone cells are responsible for the eye’s acuity, the ability to do detailed tasks like reading may diminish as can colour vision. Some people, however, never experience the full RP effects and retain their central macular vision throughout their lifetimes.

How is Retinitis Pigmentosa (RP) diagnosed?

These are exceptionally variable diseases and the symptoms are very gradual often making it difficult to diagnose in early stages. Although RP often begins in childhood, many do not experience symptoms until adulthood and thus cannot always anticipate the effects it will have on their vision. Basic methods employed to detect retinitis pigmentosa are similar to those indicating macular degeneration as they both involve looking past the pupil and into the retina to view its damage.  The most common way for a doctor to diagnose a problem with the retina is through ophthalmoscopy in which the fundus, or back of the eye, is examined to determine the extent of the retina’s damage. There are a few methods of ophthalmoscopy which can be employed: direct, slit-lamp, and indirect. In the first, an ophthalmoscope is shone into the pupil and to the back of the eye. Slit lamp is similar, but the eye is viewed in three dimensions with the use of an additional lens. Indirect ophthalmoscopy has a wider range of magnification as it is not from a small beam of direct light with lenses to direct the reflection as in the previous methods, but from a light attached to the doctor’s head while his hands may apply pressure to the open eye with a blunt instrument. The final procedure allows the entire retina to be seen at once, rather in smaller portions as with direct and slit-lamp ophthalmoscopy.

Genetic Disposition for Retinitis Pigmentosa (RP)

If a person is at risk genetically for RP, then these tests may be able to detect the problem in their early stages. There are three ways a person can be considered genetically at risk: autosomal dominant inheritance, autosomal recessive inheritance, and X-linked inheritance. Dominant inheritance occurs in a child if the parents or family members have been diagnosed with RP and it is therefore a dominant trait in their genes. If one of the parents has RP then the likelihood of the child also contracting this genetic mutation is about 50 per cent.  Recessive inheritance occurs when there is no outward sign of RP in either parent’s family.  If both parents are carriers of RP then they each have a recessive RP gene which doesn’t affect them but can be passed down to their children if the child receives both recessive RP genes. This occurs in 25 per cent of such births. Recessive inheritance also occurs in the X-linked inheritance.  In this form of RP, sons of men with X-linked RP will also inherit the condition but the daughters cannot develop this form of RP. Instead, their daughters become X-linked RP carriers. When these children become adults, the daughters will then have a 50 per cent chance of passing RP on to their sons or producing daughters who are RP carriers. X-linked RP, in contrast to most RP diseases, is also a variant of the disease which affects the macula and thus the detailed vision is compromised in early stages of the disease rather than in later stages.

Treatments for Retinitis Pigmentosa (RP)

Unfortunately, there is no cure for RP diseases and the retina will slowly get worse as more of the retina becomes damaged. This disease does not usually culminate in total blindness, however, and there are ways to slow the onset of the disease and to cope with the vision loss. Once diagnosed with any form of RP, management of symptoms involves low-vision aides, using ultraviolet protecting sunglasses to shield the retina, and learning to cope with blindness through mentoring support.  Current research on retinal cell or stem cell transplants are being conducted, but such surgical procedures are still in their early stages.

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