Additional tests can help assess your general health as well as your vision
Visual Field Testing
Your visual field is the area that you can see at any one time – whilst looking at a fixed object, it is the extent of your peripheral vision in all directions around the object. When testing your visual field, the sensitivity of your eyes at a range of points is compared to the results of an average person your age.
If your results show reduced peripheral vision, you will usually be referred for specialist investigation as this could be an indication of a number of different conditions.
FDT Field Testing
Frequency-doubling technology (FDT) is commonly used as a fast and effective method of detecting vision loss. You will be asked to look at a screen, and respond whenever you see a moving target.
FDT tests are particularly effective at detecting the early stages of glaucoma, as they specifically target the retinal receptors which are affected in this condition.
This test assesses the fluid pressure within the eyes, and is usually used as a strong indicator for the presence of glaucoma. Eye pressure can be measured with a variety of instruments, either contact tonometers which rest gently on the front surface of the eye, or non-contact tonometers, which measure the resistance of the eye to a puff of air.
Amsler charts look like squared paper, and are used to assess the function of the macula region of the retina. Certain eye conditions, such as macula degeneration and diabetes, can cause distortion to the tissues in this region, which lead to a reduction in vision. If the lines you see on the chart are wavy or distorted in any way, this could be an indication of an eye problem.
This test involves a special microscope which allows a magnified view of the eyelids and front section of the eye. It is particularly useful and commonly used in the fitting of contact lenses, removal of suspected foreign bodies in the eye and evaluation of the causes of dry eyes. It can also be used in combination with a tonometer or an additional lens to allow assessment of the retina.
This is a computer based system that gives us detailed measurements of the cornea which is used when fitting contact lenses, and is essential for the fitting of Ortho Keratology lenses such as Eyedream. The three dimensional plots produced are like Ordnance Survey maps of your eyes. The Topographer can also be used for video tear film stability testing which we use in our dry eye clinics enabling us to measure the progress of your dry eye management.
Also known as retinal photography, Fundus cameras allow digital photographs to be taken of the retina, the membrane at the back of the eye. These photographs can be compared to your previous retinal images for accurate monitoring of the progression of eye conditions such as diabetes, glaucoma and macular degeneration.
An ophthalmoscope is a device for examining the inside of the eyes to check for problems or defects. Indirect ophthalmoscopy, either with or without the use of drops to dilate the pupils, allows for a larger area of the retina to be viewed at one time. It also allows internal structures to be viewed in 3D, via a binocular view of the retina.
The cornea – the clear tissue covering the front of the eye – can vary in shape between individuals. Measurement of the shape of the cornea is performed using a keratometer, and is often done as a first step in the fitting of contact lenses. It can also be used to monitor the progression of diseases such as keratoconus, where the cornea has a more conical shape rather than the normal curve.
An orthoptic assessment consists of various tests, measuring how well the eyes work as a pair to provide clear and comfortable binocular vision. Should any problems be found, these may be alleviated using eye exercises, the addition of prisms to a spectacle prescription, or referral to a specialist where necessary.
Colour Vision Testing
Colour vision deficiencies (sometimes incorrectly called ‘colour blindness’) can affect approximately 1 in 8 males, but a much smaller proportion of females. These deficiencies can cause difficulties in recognising certain colours and confusion of similar colours, which may lead to educational difficulties. The ability to clearly distinguish colours is essential for working in certain occupations, such as the Navy and fire service.
In patients with dyslexia, it has been found that certain coloured tints cause the print on a page to appear more stable and therefore easier to read. Using a selection of coloured overlays, we can assess the colour that has the greatest effect for each individual, then prescribe reading lenses with a tint to match.