The Cirrus OCT is one of our diagnostic tools. We use it when we have seen something in the eye that we wish to examine more closely.
What is OCT?
OCT stands for Optical Coherence Tomography. It is a complex technology that looks in detail at the structure and layers of the retina.
The retina is the delicate lining at the back of the eye, similar to film in a camera. It collects light and uses this to create a picture of the world around us. An OCT scan is comparable to a MRI or CAT scan for the eyes.
What it is Used for?
We mostly use this instrument to look at two main areas of the retina. The first area is the ‘macula’ of the eye, which is the central area of the eye. This is the most sensitive part of the eye, and is the part you use when you are looking at something directly. If anything occurs in this area, it can have serious effects on your vision. Common diseases that can affect this area of your retina include age-related macular degeneration and diabetic retinopathy.
The second area we look at with the OCT is the nerve fibre layer. These nerve fibres are spread over the whole of the retina and gather together to form the optic nerve. Information is passed down this nerve to the brain where it is processed, allowing us to see. There are over 1 million individual nerve fibres. The most common diseases that affect the optic nerve are a group of diseases known as ‘glaucoma’. Glaucoma is a silent disease; it does not give you any symptoms until it is very advanced, by which time it is often too late to do anything about it.
Regular eye examinations are very important, as we can pick up signs of glaucoma while it is still in its early stages. This is particularly important if there is anyone in the family who has had glaucoma. We can use the OCT to scan the nerve fibres of the retina and look for any signs of damage long before it affects your vision.
Previously we have had to rely on the pressure readings of your eyes and the visual field (peripheral vision) test to determine whether glaucoma was beginning, but these tests have their limits. Different pressure readings will mean different things depending on the individual – a ‘high’ pressure reading may be normal for one person but cause problems for another.
The visual field test is a difficult test to perform and takes a bit of getting used to, so you need to complete the test on a number of occasions before any conclusions can be drawn from it. Also, there may be as much as 40% of the nerve fibres already damaged before the peripheral vision is affected! The OCT is much more accurate at detecting damage and detecting it earlier.
What to Expect
The test is very simple and takes just seconds to perform. There are no sudden flashes or puffs of air. It is not painful and nothing will touch your eye – all you do is look into the OCT machine. It typically does not require dilation (enlarging of the pupils using drops), although this may still be required depending on individual circumstances. Your Optometrist will be able to view the scan immediately, so will be able to discuss the results with you on the day.