Optical Coherence Tomography (OCT) is a non-invasive diagnostic technique that renders an in vivo cross-sectional view of the retina. OCT utilizes a concept known as inferometry to create a cross-sectional map of the retina that is accurate to within at least 10-15 microns. OCT was first introduced in 1991 and has found many uses outside of Ophthalmology, where it has been used to image certain non-transparent tissues. Due to the transparency of the eye (i.e., the retina can be viewed through the pupil), OCT has gained wide popularity as an ophthalmic diagnostic tool.
OCT is useful in the diagnosis of many retinal conditions, especially when the media is clear. OCT can be particularly helpful in diagnosing the below pathologies:
Macular hole
Macular pucker/epiretinal membrane
Vitreomacular traction
Macular edema and exudates
Detachments of the neurosensory retina
Detachments of the retinal pigment epithelium (e.g., central serous chorio-retinopathy or age-related macular degeneration)
Retinoschisis
Pachychoroid
Choroidal tumors
In some cases, OCT alone may yield the diagnosis (e.g., macular hole). Yet, in other disorders, especially retinal vascular disorders, it may be helpful to order additional tests (e.g., Fluorescein Angiography or Indocyanine Green Angiography).
OCT is gaining increasing popularity when evaluating optic nerve disorders by accurately and reproducibly evaluate the retinal nerve fiber layer and ganglion cell layer thickness:
Glaucoma
Optic neuritis
Non-glaucomatous optic neuropathies
Alzheimer’s disease
Anterior segment
Anterior segment OCT utilizes higher wavelength light than traditional posterior segment OCT. This higher wavelength light results in greater absorption and less penetration. In this fashion, images of the anterior segment (cornea, anterior chamber, iris and angle) can be visualized.
Because OCT utilizes light waves (unlike ultrasound which uses sound waves) media opacities can interfere with optimal imaging. As a result, the OCT will be limited the setting of vitreous hemorrhage, dense cataract or corneal opacities.
As with most diagnostic tests, patient cooperation is a necessity. Patient movement can diminish the quality of the image. With newer machines, acquisition time is shorter which may result in fewer motion related artifacts.
Optical coherence tomography angiography (OCTA) is a functional extension of OCT that provides information on retinal and choroidal circulations without the need for dye injections. With the recent development of high-speed OCT systems and efficient algorithms, OCTA has become clinically feasible.
The important difference between OCT and OCTA is: OCT images anatomical structure, whereas OCTA image’s vascular structure.
OCTA identifies blood vessels by detecting the blood flow-induced change in the OCT reflectance signal. Flowing red blood cells causes more variation in the OCT signal between repeated scans than static tissue. Multiple approaches have been described for quantifying this change through assessment of the intensity, phase, or intensity and phase of the OCT signal. Studies also showed that the derived OCTA signal is related to the speed of flowing red blood cells, where faster flow results in greater flow signal, up to a saturation limit.
Athens Eyecare Clinic provides the most modern equipment for OCT and OCT Angio, the Solix OCT from Optovue, the long-time leader in the innovation of OCT development and inventor company of OCT Angiography.
Athens EyeCare clinic in the center of Athens is one of the most complete and contemporary technologically equipped Ophthalmology clinic in Greece
