Examination of the eye with the slit lamp microscope
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Measuring the eye pressure with the most accurate method of pressure testing known as Goldman applanation tonometry, This method of pressure testing is more accurate than the air puff pressure testing.
A contact lens is placed onto the eye to examine the drainage channels within the eyeball, specifically looking to see if they are open and there is enough space for the internal fulid of the eye to access the drainage pathway. We can also see signs of previous trauma to the eye, abnormal pigment and evidence of previous inflammation, all of which can affect the eye pressure and cause glaucoma. Gonioscopy needs to be carried out by an experienced glaucoma specialist to ensure the examination is carried out precisely and the findings interpreted correctly.
In this test we measure the thickness of the cornea, the window at the front of the eye. This is a painless portable ultrasound test, quick and easy to do. We all have different shoe sizes and come tall and short and the cornea can be medium thickness, wide or narrow. This is important as we need the most accurate measurement of pressure possible. The eye pressure measuring equipment is calibrated for average thickness so if your cornea is thicker than average this means the pressure measuring test overestimates the pressure in the eye and conversely, if its thinner than average it underestimates the pressures. Precision in eye pressure measurement cannot be stressed enough as diagnosis and treatment monitoring relies heavily on accurate pressure testing.
The optic nerve is like a fibre optic cable made up of many individual nerve fibres that come together to form the nerve that senses light signals and transmits them to the brain for processing. This clever piece of technology is able to scan the optic nerve precisely, provide a 3D reconstruction and provide accurate measurements of the thickness of nerve tissue and density of the fibres at different positions within the nerve. Early glaucoma damage where only a few of the fibres are affected can be difficult to see, even with the examination microscope, however the scanner can pick up very early change meaning that the glaucoma specialist can interpret that change in a personal context for the patient. OCT scanning is quick and easy to do and it is usually carried out at every assessment. The more baselines scans you have the easier it is to detect change.
This tests the sensitivity of the peripheral vision, the first part of the vision affected by glaucoma. People do not notice that their peripheral vision has become less sensitive in the early and moderate stages of the disease. When taking the test the person is asked to look at a central spot in a white bowl and lights are shone at differing intensities around the peripheral part of their vision. You have to press a button each time you see a light. This allows accurate mapping of the peripheral vision. The visual field is also affected by other neurological conditions such as a stroke or multiple sclerosis so the results need to be interpreted by an expert. It takes time to learn how to do the test well so don’t be alarmed if you find the first few tests challenging, it usually takes 3 tries to get the technique.