What is Retinitis Pigmentosa?
Retinitis pigmentosa (RP) is a group of rare, genetic disorders that involve a breakdown and loss of cells in the retina, which is the light sensitive tissue that lines the back of the eye. Affected people often have difficulty seeing at night and a loss of side (peripheral) vision.
What causes Retinitis Pigmentosa?
RP is an inherited genetic disorder which can occur from a mutation of any of over 50 genes. These genes carry the instructions for making proteins that are needed in cells within the retina, called photoreceptors (rods and cones).
What are the symptoms of Retinitis Pigmentosa?
As retinitis pigmentosa begins as rod degeneration, the person first notices increasing difficulty with their night vision, followed by difficulty seeing in the periphery. Slow progressive constriction of the visual field leads to tunnel vision. A small area of central vision in both eyes usually persists for many years. The rate of visual loss is highly variable among individuals with RP.
How is Retinitis Pigmentosa inherited?
RP can be inherited as autosomal dominant or autosomal recessive or X-linked.
Autosomal Dominant Inheritance
In this inheritance pattern, it takes just one copy of the gene with a disorder causing mutation to bring about RP. When a parent has a dominant gene mutation, there is a 1 in 2 chance that any children will inherit this mutation and the disorder.
Autosomal Recessive Inheritance
In autosomal recessive inheritance, it takes two copies of the mutant gene to give someone the disorder. An individual with a recessive gene mutation is known as a carrier. When two carriers have a child, there is a:
- 1 in 4 chance the child will have the disorder
- 1 in 2 chance the child will be a carrier
- 1 in 4 chance the child will neither have the disorder nor be a carrier
In this form of inheritance, mothers carry the mutated gene on one of their X chromosomes and pass it to their sons. Because females have two X chromosomes, the effect of a mutation on one X chromosome is offset by the normal gene on the other X chromosome. If a mother is a carrier of an X-linked disorder there is a:
- 1 in 2 chance of having a son with the disorder
- 1 in 2 chance of having a daughter who is a carrier
How is Retinitis Pigmentosa diagnosed?
RP is diagnosed by an ophthalmologist after a detailed eye examination. It often requires confirmation with electroretinogram (ERG) findings of reduced rod/cone function.
How is Retinitis Pigmentosa treated?
There is no cure for patients with RP and assistance is given with low vision devices. Gene therapy and retinal implants are still at the research stage.
Behaviours or conditions that might indicate Retinitis Pigmentosa
- Difficulty seeing in changing levels of light (light to dark or dark to light) whether that is inside or outside, such as times of day when the light changes (night or dawn or dusk or very cloudy days); transitions from indoor to outdoor environments or vice versa and/or trying to see clearly in darker environments.
- Difficulty with bright lighting or sunlight; avoidance of bright places; squinting or closing eyes when outside.
- Difficulty with glare on reflective surfaces such as whiteboard, laptop screen, puddles and wet surfaces on footpath.
- Bumping into, tripping into or clipping corners of objects on the right, left, upper or lower periphery while moving.
- Unaware of objects, obstacles or hazards on the right, left, upper or lower periphery.
- Missing information on worksheets, the whiteboard and other surfaces that reside in the periphery.
- Only seeing parts of the whole when viewing larger information that extends outside central vision
- Movement of head to scan to take into reduced peripheral vision (tunnel vision).
What to do
- The young person should visit an optometrist or ophthalmologist to determine diagnosis and cause and to map fields, if developmental age permits;
- A Functional Vision Assessment will assess the infant, child or young person’s use of vision.This will include observations and assessments of how he/she uses vision in real life situations and for learning and access to Te Whāriki, the New Zealand Curriculum, the Blind and Low Vision Education Network, NZ (BLENNZ) Curriculum and the Expanded Core Curriculum. Adaptations or modifications to the environment and materials used may be required. Some of these can include lighting review and monitoring glare to reduce fatigue and maximise access. Strategies and suggestions for low and high tech devices to assist the learner’s functional vision are also included in the functional vision assessment. Some of these strategies can include a review of print size, contrast levels and the effects of clutter.
- A Developmental Orientation and Mobility assessment will assess how the infant, child or young person moves purposefully, safely and confidently in the environment and how they understand where they are in space and what is around them.