About The Eye

Parts of the eye and how they work?

Our ability to "see" starts when light reflects off an object at which we are looking and enters the eye. As it enters the eye, the light is unfocused. The first step in seeing is to focus the light rays onto the retina, which is the light sensitive layer found inside the eye. Once the light is focused, it stimulates cells to send millions of electrochemical impulses along the optic nerve to the brain. The portion of the brain at the back of the head interprets the impulses, enabling us to see the object.

The white part of your eye is called the sclera. It is a tough cover that protects your round eyeball. Part of it stretches and bulges out over the middle of the eye. This part is clear to let light through and is called the cornea. The drawing below shows the inside parts of your eyes.

The coloured ring is the iris and the black hole in the middle is the pupil. Light rays get inside your eye through the pupil. Behind the pupil is a lens, a bit like the lens in a camera or slide projector - it is used to focus and helps you to see things clearly. Special muscles stretch and relax the lens to change focus. Inside the eye the space is filled with a clear jelly, called the vitreous, to keep the eyeball round.

The retina lines the inner two thirds of the eye and catches the light coming through the lens. The light is then converted into electrical signals which travel down the optic nerve.

The Eye Examination

If you have not had your eyes tested before it can be a pretty daunting experience. This section is to try and allay some of those fears and answer some commonly asked questions.

During the examination (or sight test) you will be asked to read from a chart whilst various lenses are placed in front of your eyes.

Together we will determine whether your vision has any deficiency and, if a correction is required, the effect of this can be demonstrated using sample lenses (known as trial lenses). This enables us to demonstrate the benefits of any lenses prescribed before they are dispensed. We will also look into your eyes with an instrument similar to a handheld microscope and may use various other items of equipment to check the pressure within your eyes and your field of vision.

The exact procedures during an eye examination vary from patient to patient depending on a number of circumstances such as age, health and any family history of eye disorders (such as glaucoma).


If, at any time during your visit to our practice, we use terminology that you don't fully understand, then please feel free to ask us for an explanation. Meantime, here is a list of common ocular conditions that we come across.

Important : This glossary lists a few of the better known ocular conditions and abnormalities (in alphabetical order) and is intended as a guide only. Patients experiencing loss or blurred vision or any pain in the eye, however caused, should seek urgent medical advice immediately.


The ability for the eye to increase its positive power thereby facilitating the normal eye to focus on objects nearer the viewer. This is necessary when reading, for example. As we get older the amount of accommodation possible reduces due to a loss of elasticity within the eye and reading may become more difficult, necessitating extra help for reading, generally in the form of spectacles.


A condition where the image falling on the retina is not equal in all meridians, causing blurring. It is caused by either the front or back of the eye being non-spherical (i.e. instead of being round, the surfaces may be shaped more like a rugby ball). This prevents the rays from forming a sharp focus. Generally the condition is simply corrected by the use of astigmatic or toric lenses which themselves have different powers over their surface correcting the fault within the eye. Astigmatism can equally affect both Myopic or Hyperopic patients.

Detached Retina

A condition in which part of the Retina (the layer within the eye which receives the image) becomes separated or detached from the inside of the eye. Symptoms include a sudden loss of vision over the area of vision affected. The condition is more common in myopic patients and the elderly. Prompt treatment involving laser surgery can often correct the condition, although patients generally suffer some permanent reduction in their visual field.


This can often be detected in an eye examination and the patient referred to their GP for treatment. Apart from the general effects of the condition, Diabetes if left untreated can cause major complications in the eye, particularly in later life and for this reason diagnosed patients are entitled to free NHS eye examinations.


An eye disease displaying an increase in the pressure within the eye (intraocular pressure) which, if untreated, can cause loss of vision and potentially blindness in the affected eye. During an eye examination, patients may be tested for signs of this condition. Patients who have direct family members suffering from this condition should have routine examinations on a regular basis (at least every 12 months). Patients over the age of 40 and with a mother, father, brother or sister, who have been diagnosed as suffering from glaucoma, are entitled to a free NHS eye examination.

Hypermetropia (Long Sighted)

A condition of the eye in which distant objects are focused behind the retina when the eye is in a relaxed state (see Accommodation) causing vision to be blurred. People with this condition are also known as, Hyperopic, Long sighted or Far sighted. The condition is corrected by the use of positive powered lenses.


A painful condition typified by swelling of the Iris (the circular coloured section of the eye surrounding the pupil). Symptoms include blurring and loss of vision. The condition is treatable with medication.


Patients suffering from Keratoconus have a thinning of the central portion of the cornea causing the cornea to adopt a slight cone shape. This prevents the formation of a sharp retinal image, causing blurring of vision. This condition is generally corrected with the use of contact lenses.

Macular Degeneration (ARMD Age Related Macular Degeneration)

A condition affecting mainly the elderly in which the vision becomes progressively impaired, generally in both eyes. It is caused by a degeneration of the receptors of the eye and affects mainly the central areas of vision. Treatment is normally restricted to the use of Low Visual Aids (powerful forms of magnifying lenses) but in some forms of disease, treatment by laser can arrest the condition.

Myopia (short sighted)

The condition of the eye in which distant objects are focused in front of the retina when the eye is in a relaxed state (see Accommodation), causing the image to be blurred. People with this condition are also known as, Short sighted or Near sighted. The condition is corrected by the use of negative powered lenses.


With increasing age the eye becomes less flexible and is unable to deliver the amount of extra positive power to view close objects (see Accommodation). This extra power is generally delivered by supplying the patient with reading glasses or alternatively a bifocal or varifocal lens, which will ensure sharp vision for both distance and reading.

Strabismus (squint)

Patients suffering from this condition have difficulty in fusing the images within each eye to produce a single image. This can cause double vision and in certain cases the two eyes will not appear to be looking in the same position. The condition can often be corrected by the use of spectacles, particularly in young children, together with ocular exercises. However, in some cases a simple surgical procedure is necessary.

Frequently Asked Questions

Here are some commonly asked questions:

Why Have My Eyes Tested?

The eye examination is a quick and effective method of determining any visual disorder or imbalance that may or may not require correcting with spectacles or contact lenses. It also offers an invaluable opportunity to examine the internal structure of the eye and to detect the presence of certain disease - Glaucoma or Diabetes for example.

How Often Should I have My Eyes Examined?

Normally visiting us once every one or two years is sufficient. In certain circumstances, we may wish to see you more regularly, ie for young children or diabetics and we will advise you if this is the case. For patients with diabetes and glaucoma, or a history of glaucoma in the family then the recommended interval is 1 year.

The important thing to remember is that your eyes are terribly important and need regular check-ups. Certainly, in the case of eye disease, as in all illnesses, the earlier a problem is diagnosed, the earlier treatment can commence and the more successful it will be. Remember you only get one set of eyes.

Should My Children Have Their Eyes Examined?

The answer is definitely YES although, as a general rule, it is not normally necessary for children to undertake routine examinations until they reach school age.

However, a surprising number of new born children have vision irregularities, usually of a minor nature. So, if you suspect that your child has defective vision then you should contact us immediately. You will be relieved to know that babies of just a few months old can be examined and almost all defects can be overcome.

Incidentally, your child's eye examination is paid for by the NHS and vouchers are available if spectacles are required.

If you have any questions about the eyecare of your children, then please do contact us for helpful (and free) advice.