At Peel Vision, we use the latest-generation Spectral Domain OCT (SD-OCT) scanner from Zeiss Technologies, the Cirrus HD-OCT 5000 with Fast-TracTM
What is an OCT scan?
An OCT (Optical Coherence Tomography) scanner is an ultra-high resolution camera that takes cross-sectional images of vital structures at the back of the eye (the retina and optic nerve). It is a very important tool used for the diagnosis and monitoring of a wide range of sight-threatening conditions, including macular degeneration, glaucoma and diabetic retinopathy.
OCT works on a principle like ultrasound to map out the layers of the back of the eye. However, instead of using sound waves, it uses near-infrared light waves. These light waves are projected and then reflected off the retina and optic nerve at the back of the eye. The reflected light waves are then measured and converted by a computer into high-resolution 3D color images using complex Fourier analysis. OCT is 10 times more sensitive than ultrasound, and can produce images with near-microscopic resolution as high as 3-10 microns. It allows the smallest of pathologies or changes to be detected at the back of the eye, well before the naked eye can see it.
How is an OCT performed?
OCT is a safe, fast and non-invasive test performed in our clinic, usually by our experienced Ophthalmic Assistants. The results are then analyzed and interpreted by Dr Then.
Patients are seated comfortably in front of the scanner, and their chin placed on an electronically-adjustable chin rest. Each eye is scanned separately. Our experienced Assistant will align the eye with a focusing target, which the patient will see as a flashing green-star, and will then commence the scan with the push of a button. The scan takes only a few minutes to perform per eye.
What is an OCT scan used for?
OCT scanning does not replace clinical examination by the ophthalmologist, but is a very useful adjunctive tool to aid early diagnosis, and to detect early change in chronic eye conditions such as macular degeneration and glaucoma. It is used most commonly in:
1. Dry MD. An OCT scan may detect conversion to wet MD much earlier than could be detected with the naked eye on clinical examination. This allows earlier diagnosis, and earlier treatment, which is vital for a better visual prognosis.
2. Wet MD. An OCT scan may be used to help confirm the diagnosis of wet MD, and is always performed before the application of regular anti-VEGF intravitreal injections.
Glaucoma is a chronic disease in which a high intraocular pressure within the eye causes progressive damage of the optic nerve, leading to loss of peripheral and central vision. Diagnosis depends on clinical examination of the optic nerve, as well as measurement of the eye pressure and visual fields. A high-resolution image of the optic nerve with the OCT complements these other clinical measures, and can help with earlier diagnosis as well as early detection of change in the optic nerve over time, which allows optimization of treatment.
Diabetes can potentially affect the circulation in the retina at the back of the eye, leading to leakage and bleeding from abnormal blood vessels. If this affects the macula (diabetic maculopathy), it can lead to rapid and significant vision loss. Whilst the changes are usually apparent on clinical examination of the back of the eye, the high-resolution images of the OCT may help to detect and confirm these changes earlier, and will also assist in monitoring the response to treatments such as laser and intravitreal injection therapy.
Retinal Vein Occlusions.
Blockage of the veins in the retinal circulation at the back of the eye can result in significant leakage and bleeding throughout the retina, and is particularly visually significant if it affects the macula. OCT scans of the macula in this condition can also help diagnose and monitor changes as treatment is applied.