University of Edinburgh
 

Medical Information on Sector Retinitis Pigmentosa

by Dr Andrew Blaikie for VI Scotland

This document is written with the minimum use of medical terms and jargon. It is impossible to avoid all medical terms but where we have used them we have attempted to explain them as clearly as we can. Although the information is intended to describe most aspects of the condition each child is different and there will always be exceptions to the rule. As far as we can determine these pages are true and accurate and have been written in good faith.

What this information is not for

This document is not a substitute for a consultation with a Health Professional and should not be used as a means of diagnosing a condition.

We hope the information will help you to:

  • Have a better understanding of the condition
  • Know what tests and treatments are normally available
  • Know when to seek professional advice
  • Be able to discuss the condition in a more informed way
  • Make the most of consultations with carers, teachers and health professionals
  • Be reassured and more able to cope

Due to staffing limitations we are not able to offer telephone or email advice to parents of children.

Medical Information on Sector Retinitis Pigmentosa

What we see is made in the brain from signals given to it by the eyes. What we see is in fact made in the brain. The brain makes sight from signals given to it by the eyes.

What is the normal structure of the eye?

The eye is made of three parts.

  • A light focussing bit at the front (cornea and lens).
  • A light sensitive film at the back of the eye (retina).
  • A large collection of communication wires to the brain (optic nerve).

A curved window called the cornea first focuses the light. The light then passes through a hole called the pupil. A circle of muscle called the iris surrounds the pupil. The iris is the coloured part of the eye. The light is then focused onto the back of the eye by a lens. Tiny light sensitive patches (photoreceptors) cover the back of the eye. These photoreceptors collect information about the visual world. There are two types of photoreceptors named by their shape when looked at in fine detail. They are called ‘rods’ and ‘cones’.

Rod and Cone Photoreceptors are good at seeing different things

Rods are good at ‘seeing’:

  • things that move
  • in the dark
  • but only in black and white
  • and in less detail.

 Cones are good at ‘seeing’:

  • things that are still
  • in daylight
  • in colour
  • and in fine detail.

The covering of rod and cone photoreceptors at the back of the eye makes a thin film called the retina. The central bit of the retina is made up of cones. They help us see the central bit of vision that we use for reading, looking at photographs and recognising faces. The area of the retina around the central bit is made up of rods. The rods see the surrounding bits of vision and help us to walk around and not bump into things especially in the dark. Each photoreceptor sends its signals down very fine wires to the brain. The wires joining each eye to the brain are called the optic nerves. The information then travels to many different special ‘vision’ parts of the brain. All parts of the brain and eye need to be present and working for us to see normally.

What is Retinitis Pigmentosa?

Retinitis Pigmentosa is the name given to a wide range of eye conditions. ‘Retinitis’ means disease or inflammation of the retina. ‘Pigmentosa’ refers to how the retina can look in this condition (the retina can often develop lots of small, dark specks of pigment). Retinitis Pigmentosa eye conditions are all linked by a problem with the rod and cone photoreceptors. The photoreceptors either work poorly from the day a child is born or else slowly stop working over a period of time. Usually the rods are affected more than the cones. Some Retinitis Pigmentosa conditions do not only affect the eye but may also affect the rest of a child’s body.

Sector Retinitis Pigmentosa

Sector Retinitis Pigmentosa is a rare form of the condition. In most cases of Retinitis Pigmentosa the whole of the retina is affected but in Sector Retinitis Pigmentosa only one area of both eyes is affected. Typically it is the lower nasal parts of the retina. Sector Retinitis Pigmentosa is often inherited in an autosomal dominant pattern. This means that a parent or grandparent often also had the condition and ‘passed it on’ although they may not have had any symptoms and so were never diagnosed with the condition. In about half of cases there is no family history but the affected person could still pass it on to their children.

There are many reasons why a child might develop Retinitis Pigmentosa

Retinitis Pigmentosa is caused by a misprint in the child’s genes. Genes are a chemical alphabet stored in the body. Genes contain the body’s “built-in” plan to make sure all the parts of the body work correctly. If a gene has a misprint in the chemical alphabet then a part of the body may not work correctly. Sometimes many parts of the body do not work correctly. A child with Retinitis Pigmentosa has often been passed (inherited) a gene with a misprint in it from one or both parents. Sometimes by chance a new misprint occurs in the child’s genes and the parent’s genes are normal. There are many different ways a child can ‘inherit’ a condition.

How is the diagnosis made?

There are special tests that can be done to help the eye doctor decide what is wrong. These tests measure signals from the eyes when a child is shown a bright light. Sticky patches are placed around the eyes. The sticky patches are attached to wires that lead to a machine. The machine records the electrical signals made by the eyes. The record of the signals will help the doctors decide what the matter is. If the signals are weak or absent then Retinitis Pigmentosa is more likely. This test is called an Electroretinogram (ERG).

How does Sector Retinitis Pigmentosa affect the way a child sees

The good thing about sector Retinitis Pigmentosa is that it rarely affects central vision and most patients are unaware that they have the condition. It does however cause peripheral visual field loss and this may mean that patients with the condition will not satisfy the DVLA requirements for holding a driving licence.

Who wrote these documents?

These pages are the consensus of opinion of many different people. They include parents of visually impaired children, visually impaired children themselves, Community Paediatricians, Ophthalmologists, Educationalists and Psychologists.

The main author and person responsible for their content is Dr Andrew Blaikie who worked as an Ophthalmology Research Fellow with Visual Impairment Scotland and is a member of the Royal College of Ophthalmologists.

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