Optical Coherence Tomography

Imaging the retina. Thinkstock

What is an OCT?

Optical coherence tomography (OCT) is a noninvasive imaging technology used to obtain high resolution cross-sectional images of the retina. OCT is similar to ultrasound testing, except that imaging is performed by measuring light rather than sound. OCT measures the retinal nerve fiber layer thickness in glaucoma and other diseases of the optic nerve.

Learning more about OCT

Optical Coherence Tomography, also referred to as OCT, is a way for optometrists and ophthalmologists to image the back of the eye including macula, optic nerve, retina and choroid.

During an eye examination, optometrists and ophthalmologist can view the back of the eye and its anatomy. However, sometimes doctors need more detail or need to inspect detail right below the surface which is difficult to view with standard techniques. In some ways, it can be compared to doing an "MRI of the retina."  Some describe it as an optical ultrasound because it images reflections between tissues to provide doctors with cross-sectional images.The detail that can be visualized with an OCT is at such high resolution that doctors are seeing things never been seen before in a living human eye. It actually images detail better than 10 microns, which is better than MRI or ultrasound. As a result, instead of looking into the eye and guessing that their might be retinal swelling simply by the way it looks, an OCT will give us detailed information and actually show exactly what layer of the retina is accumulating fluid causing edema or swelling.

It can be used to track healing or resolution of that swelling.

Optical coherence tomography works by using interferometry. Interferometry enables eye care professionals to image tissue with light rather by X-rays, sound or radio frequency. It works by shining a beam of light into the eye.  Part part of this light is reflected by different tissues.

Images are built based on this internal reflection differential. An OCT images to approximately 2-3 mm below the surface of the tissue. Images are obtained clearly through a transparent window, such as the cornea. The light that is emitted into the eye is safe. The output is near infrared light so no damage to the eye will occur.

What happens during an OCT?

An OCT may very well be the easiest medical imaging test you will ever take. The test takes only about 5 minutes to perform. With most OCT machines, you simply place your head in a head rest. The technician will calibrate the instrument. You will be instructed to look at a light target inside the machine. The technician will then receive the image. If your pupils are very small or if the doctor wants image a very specific area, your pupils will be dilated with medicated eye drops. Most people do not require dilation.

An OCT is particular use in evaluation many eye conditions, including:

  • macular degeneration
  • macular holes
  • pre-retinal macular fibrosis (cellophane maculopathy)

An OCT represents some of the latest technological advances in eye care that can be delivered at a very low cost to the patient. In most cases, the cost of an OCT test is $75-125.

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