Optical Coherence Tomography
Introduction
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| OCT scan showing dark, fluid-filled spaces present in retinal oedema. |
Optical Coherence Tomography (OCT) uses reflected light to analyse the microscopic structure of the retina of the eye in the same way that ultrasound waves can be used to examine internal body structures.
It is possible to scan both the central retina and the retina around the optic nerve.
Macula OCT scans
The macula is the central area of the retina. It can be affected by many different diseases. The most common is age related maculopathy (ARM), often known as ‘macular degeneration’.
The macula area can become swollen after routine cataract surgery. In some patients fluid leakage is so severe that the results of surgery are threatened. OCT can detect swelling even when it is not possible to see it with normal clinical examination tools. This information can be used to initiate and guide treatment.
Optic disc OCT scans
Nerve fibres converge from all over the retina and travel back to the brain via the optic nerve head, also known as the optic disc.
OCT can be used to measure the thickness of the nerve fibres and compare the results to both normal patients, and make a direct comparison between someone’s right and left eye.
Glaucoma and OCT
Glaucoma is a disease in which the nerve fibres of the retina and optic disc are damaged. Untreated it can lead to blindness.
In glaucoma OCT can be used in several ways:
- As a baseline test for later comparison
- To distinguish between glaucoma and normal variations of the optic disc
- To distinguish between glaucoma and other diseases that affect the optic disc
- To help confirm the diagnosis of glaucoma and provide a baseline for future comparisons
- To determine whether further damage to the optic nerve is occurring despite glaucoma treatment
Frequency of scans
How often OCT needs to be performed depends on the purpose of the test. In active retinal disease scans may need to be taken every few weeks. In glaucoma it is more common for scans to be performed every two to three years.
Safety of OCT
OCT uses reflected light and will not damage your eye.
Having an OCT
An OCT scan takes about fifteen minutes. The test is easy to perform and painless. You simply need to look at a flashing fixation target.
Pupil dilation
In most cases the pupils will need to be dilated. It is legal to drive with dilated pupils although some patients find it difficult to do so and it is always wise to bring a driver.
Costs
OCT is a relatively expensive test because of the high cost of the machine. You may be eligible for reimbursement by your insurance company.
