Visually Impairing Conditionsby Dr Andrew Blaikie for VI Scotland
Medical Information on Hypermetropia
For whom is this information intended?
The information contained in this document is intended for use primarily by parents, other members of the family and older children with visual impairment. The information will also be of use to interested health professionals, carers and teachers.
The purpose of each information document
The purpose of the information is to explain:
- The way the eyes and brain normally work to make 'vision'
- The reason why vision may become impaired by a specific condition
- The cause of the condition
- The effects of the condition on the child's vision
- How the condition is diagnosed
- What can be done to help
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. Inevitably there will be some mistakes. We apologise for this.
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
After reading the information we hope you will:
- 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
These pages represent the consensus of opinion of many different people who 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 is an Ophthalmology Research Fellow with Visual Impairment Scotland and a member of the Royal College of Ophthalmologists. We are very keen that parents and children feedback to VI Scotland about these information documents. If you have any questions or comments regarding the information please contact:
Visual Impairment Scotland
Scottish Sensory Centre
The University of Edinburgh
Edinburgh EH8 8AQ
Telephone Number : 0131 651 6078
Fax Number : 0131 651 6502
Textphone : 0131 651 6067
Medical Information on Hypermetropia
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. The covering of photoreceptors at the back of the eye forms a thin film known as the retina. 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 the parts of the brain and eye need to be present and working for us to see normally.
What is Hypermetropia?
Hypermetropia is also known as 'long-sight'. This means that a child who is 'long-sighted' is more likely to see better at 'long' distance than 'short'. Often children with Hypermetropia can see clearly when watching the television or the blackboard but may find reading a book difficult. They may have to focus very hard to see near things clearly. This may cause eye strain and headache.
Mild Hypermetropia is a common and normal finding
Mild hypermetropia is a common and normal finding in most young children. Many children 'grow out' of hypermetropia by adulthood.
Why can objects at long distance be seen clearly but not at short distance?
For clear and comfortable vision light must be focussed sharply onto the retina at the back of the eye. Most hypermetropic eyes can focus the light from a far object. Many hypermetropic (or long-sighted) eyes have difficulty focussing the light from an object at short distance. Instead the light focuses to a sharp point in behind the retina. The vision is then blurred. If the object is taken further away from the eye, the point at which the light focuses sharply will move forwards onto the retina. An object at a longer distance then becomes clear: the eye is 'long-sighted'.
Smaller eyes tend to be Hypermetropic
The smaller and shorter an eye is, the more likely light from a distant object will focus beyond the retina. The focussing power of the cornea and lens are also important in causing hypermetropia.
What is the cause of Hypermetropia?
There are a few reasons why a child might develop Hypermetropia. Some of these include:
- Their parents are hypermetropic (long-sighted) and they 'inherit' Hypermetropia
- They have an eye condition that may cause Hypermetropia
Most children are long sighted by chance. They do not have a parent with long sight or any other condition of their eye.
Hypermetropia can often be caused by other eye conditions
For normal growth of the eye light needs to enter the eye without being blocked. If a child has a hazy cornea (corneal dystrophy) or lens (cataract) not all the light can enter the eye and the vision will be blurred. This disturbs the normal growth of the eye. This may lead to hypermetropia.
Other conditions such as Retinitis Pigmentosa and Microphthalmia can also be associated with hypermetropia. See the VI Scotland information sheets on these conditions.
Hypermetropia can often be seen along with other eye conditions
The smaller and shorter an eye is the more likely it is to develop other eye conditions. These include:
What is Glaucoma?
Glaucoma is when the optic nerve is damaged by high pressure in the eye. This can cause visual impairment. The particular type of glaucoma that a hypermetropic eye is prone to is called 'Acute Close Angle Glaucoma'. This often causes pain, red eye and blurred vision. This only very rarely causes problems in childhood. See the VI Scotland Document on Glaucoma.
What is a Squint?
A squint is when a child's eyes do not appear to be both looking in the same direction. Sometimes in Hypermetropia one eye can point inwards (converge). This is called a convergent squint. A squint can often be improved with spectacles or an operation.
What is Amblyopia?
If light from an object cannot be focused sharply on to the back of the eye then the child may develop a 'lazy' eye. This is also known as Amblyopia. It is not actually the eye that has become lazy; it is the special vision parts of the brain. The brain can only learn to see as clearly as the picture given to it by the eyes. If the brain has not been given a sharp, clear picture by the eye because of hypermetropia then it cannot learn to see clearly. If spectacles are worn to help focus the light then amblyopia may be prevented. Sometimes however even with correct spectacles vision may still be blurred. This is because the brain has not developed the power to see clearly. This is called Amblyopia. Amblyopia is more common in a child who also has a squint. See the VI Scotland Document on Amblyopia.
How is Hypermetropia diagnosed?
Sometimes parents and teachers notice, by the way a child acts, that their vision might be impaired. Children may have difficulty seeing text books at school. They may complain of eye strain or headache. Parents may notice that their child's eyes also occasionally squint. If parents discuss their concerns with their Family Doctor an assessment can be arranged. The family doctor may initially suggest an appointment with an optometrist.
An optometrist can diagnose hypermetropia during an examination. The level of hypermetropia can be measured by shining a light through different lenses into the eye. The level of hypermetropia is measured in focussing power units called 'dioptres'. Plus units are used to describe Hypermetropia. Mild hypermetropia is between zero and plus three dioptres. Moderate hypermetropia is between plus three and ten dioptres. Severe or 'high' hypermetropia is greater than plus ten dioptres.
What can be done to help?
Spectacles or contact lenses can usually sharpen vision. Sometimes the vision will not be perfect. This can be because of other problems with the eye such as microphthalmia, squint and amblyopia.
Other eye conditions such as squint can be treated by operations and wearing spectacles.
Laser surgery has been used successfully to treat short sight in adults and even some adults with long sight. It involves altering the shape of the cornea to focus light from objects on to the back of the eye. Because the level of hypermetropia can change during childhood and the early twenties it is never performed on children.
How can parents, family, friends and teachers make a difference?
We use our vision to get around, learn new things and to meet other people and make friends.
It is important that children are encouraged to wear their spectacles or Low Visual Aids (LVAs). This will help the child see more clearly. It will also help the vision parts of the brain to grow and develop correctly.
Even if a child has very poor vision many useful and practical things can be done to help.