Ocular Coherence Tomography (OCT) is an exciting new technique for examining the internal structures of the eye. The most common present applications are looking in fine detail at the retina and optic nerve although anterior segment OCTs have also been developed to examine the cornea, iris and lens. OCT uses the principle of light interference to form a cross-sectional map of the retina or optic nerve. A super-bright light source such as a special LED is used and a beam-splitter is used to form a reference and a scanning beam. The reference beam is reflected by a reference mirror and is re-combined with the reflected scanning beam from the eye. A computer analyses the interference patterns which result. By varying the position of the reference mirror, different depths of the retina can be studied. The scanning beam is traced across the retina by a computer controlled mirror which can move the point in a horizontal, vertical or any oblique direction. The most common strategies used for looking at the retina with this type of OCT use a series of intersecting scans in different meridians. This is analogous to scanning from 12 O'clock to 6 O'clock and then from 1 to 7 and so on. Following the scan, a map is built up of the area being scanned and presented in comparison to age-matched controls. The latest OCT scanners use a newer technique known as spectral domain OCT. This is a technique where the individual freqencies of the light are used separately to build up an image without the need for scanning the spot on the retina. This increases the speed, accuracy and reliability of the scan. As the OCT gives an accurate cross-section of the retina, it is very useful for the diagnosis of many diseases. Such diseases include macular holes (a full thickness hole of the retina), central serous retinopathy (the accumulation of fluid beneath the retina) and macular edema from diabetes or retinal circulation problems. One of the most important new applications of the OCT is in the monitoring of the response of the retina to Lucentis. Lucentis is an exciting new drug used in the treatment of wet age related macular degeneration (AMD). Tiny quantities of the drug are injected into the eye to treat this devastating disease. The OCT has been proven to be the best way of monitoring the response and determining the need for further injections. OCT testing is widely available, including at our clinic.
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