The scan shows swelling, drusen, and holes in the macula. Optical coherence tomography gives a cross-sectional view of the retina, so the doctor sees the layers from the side, like a slice through the tissue. That view captures macular edema, which is swelling, plus drusen and macular holes. Drusen are light-yellow deposits under the retina. The scan also shows vitreous traction, meaning pulling by the gel inside the eye. Bent lines and dim central vision point straight to the macula, so this is the right test for her complaint.
The machine works with light, not sound. It is noninvasive and noncontact, and it reads reflections of light coming back from inside the tissue. Think of it as an optical ultrasound. Its detail is finer than 10 micrometers, which beats both ultrasound and magnetic resonance imaging. The parts of the system are a light source, a light detector, a beam splitter, and a movable mirror. The result is a 3-dimensional digital image of the retina, optic nerve, or anterior chamber angle. The data can be compared with the patient's earlier scans or with values from a matched group of people. In glaucoma, that comparison tracks the retinal nerve fiber layer.
Tell patients the truth in one line: the scan uses light, takes seconds, and never touches the eye. Then remember what it measures, which is the shape and thickness of tissue layers. It does not measure vision, pressure, or corneal cells. Knowing what tomographic imaging reports belongs to the COA ophthalmic imaging content area.
Incorrect Answers
- A. Counting the cells at the back of the cornea is the job of a different corneal instrument. An OCT scan of the macula looks at the retina instead.
- B. Telling faint shades of gray apart is measured by a vision test the patient performs. OCT records tissue structure and asks nothing of the patient's judgment.
- C. Fluid pressure inside the eye is measured with a tonometer. OCT reports pictures and thickness values, not pressure in millimeters of mercury.
Testing Pearls
- OCT is noninvasive and noncontact and uses reflected light.
- It gives a cross-sectional image with detail finer than 10 micrometers.
- Macular findings include edema, drusen, vitreous traction, and holes.
- OCT also images the optic nerve and the anterior chamber angle.
- Scans are compared with the same patient's earlier images to judge change.
References
- American Academy of Ophthalmology. Ophthalmic Medical Assisting: An Independent Study Course. Chapter 10, Adjunctive Tests and Procedures.
