Optical Coherence Tomography (OCT)

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New and exciting technologies have emerged to examine the various parts of the eye. OCT is the most valuable advance in retinal diagnostic imaging in decades. The OCT is like an MRI of the eye. It provides a cross sectional analysis of the eye structures including the retina. OCT imaging allows optometrists and ophthalmologists to see pathologies that lurk underneath the retina and thus were in some cases difficult to identify with previous imaging and microscopic examination. The newest OCT instruments allow for identification in 5 micron increments. (5 microns is about the size of a red blood cell). 

OCT imaging has far reaching ramifications in the diagnosis and treatment of many common serious ocular conditions. Let’s examine a few of them individually and better understand what diagnostic information the OCT imaging provides the eyecare practitioner.

Glaucoma: Glaucoma is a disease of the optic nerve fibres and results in a loss of peripheral vision if not treated and controlled in a timely fashion. In the majority of cases glaucoma has no symptoms in the early stages. OCT scans provide information on  thickness of the cornea (thin corneas are associated with glaucoma) and the density of the optic nerve fibre layer. The optic nerve is like a fibre optic cable with millions of individual wires that send the electrical impulses from the photoreceptors in the retina to the brain for processing.   Thinning of the nerve fibre layer is a precursor to the peripheral vision loss that ultimately results from glaucoma. OCT also gives information about the anterior chamber drainage angle. The “angle” is the space where the fluid in the eye circulates out and into the blood stream. Narrow drainage angles can cause a particular type of glaucoma known as narrow angle glaucoma. One of the emerging diagnostic tests that the OCT can provide is the ganglion cell complex.  The ganglion cells are connected to the nerve fibre layer and research shows that thinning at this level can even precede thinning of the nerve fibre layer and thus gives the eyecare practitioner a very early indication of glaucomatous disease.

Macular Degeneration:  The macular area is the part of the retina that you use to see faces and colour. The macula is the centre most part of your vision and when damaged can cause devastating consequences to visual function. AMD or age-related macular degeneration is the leading cause of blindness in North America.  AMD can be detected and monitored in a number of ways including biomicroscopic examination of the retina. But the OCT provides an unprecedented look underneath the retinal layers to better monitor the disease for progression and determine if leakage is present (the “wet” form of the disease). It is becoming a very important test in the management and diagnosis of AMD.

The OCT is the newest diagnostic instrument in our South Cowichan office. It has allowed us to explain why some people have decreased visual acuity despite the fact that the retina looks normal on the surface with biomicroscopy.  We are better able to diagnose and monitor glaucoma and various retinal diseases; and it has allowed certain pathologies to be diagnosed and treated which may have otherwise gone undetected.

Written by Cowichan

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