What to Expect from Your Laboratory Test: Purpose, Procedure, Results, and Possible Risks

This test is a laboratory analysis that helps your healthcare provider evaluate how your body is functioning and look for signs of illness. Your doctor may order it as part of a routine checkup, to investigate symptoms you are experiencing, or to monitor a condition you already have and track how well your treatment is working.

This test uses Optical Coherence Tomography (OCT) to measure the thickness of the retinal nerve fiber layer (RNFL) in the right eye at the clock hour 1 position. The retinal nerve fiber layer consists of nerve fibers that carry visual information from the retina to the brain. OCT is a non-invasive imaging technique that uses light waves to create detailed cross-sectional images of the retina, similar to how ultrasound uses sound waves.

The test is usually performed by collecting a small sample, such as blood, urine, or another body fluid, which is then sent to a laboratory for analysis. A trained healthcare professional will gather the sample, often using a needle inserted into a vein in your arm. The procedure typically takes only a few minutes, and you can usually return to your normal activities right afterward.

During the test, you will sit in front of the OCT machine and rest your chin on a support. The technician will align your eye with the scanning beam. You will see a brief flash of light as the scan is taken. The process is completely painless and takes only a few minutes. No eye drops, needles, or blood samples are required. You may need to avoid wearing eye makeup or contact lenses on the day of the test.

Your results are compared against established reference ranges, which show the levels typically seen in healthy people. Values that fall within these ranges are considered normal, while results that are higher or lower may point to a condition that needs further attention. Keep in mind that an abnormal result does not automatically mean you are ill; your doctor will interpret the findings alongside your symptoms, medical history, and other tests before making any diagnosis or recommending next steps.

The test results show the thickness measurement in micrometers (μm). Your results will be compared with a database of normal eyes based on your age and ethnicity. Thinner than normal RNFL may indicate damage to the optic nerve, which can occur in conditions like glaucoma. Your eye doctor will interpret the results in combination with other eye examinations and tests.

This test is generally very safe and carries minimal risk. If your sample is collected with a needle, you may feel a brief sting or pinch, and some people develop mild bruising, soreness, or slight bleeding at the puncture site. These effects usually go away within a day or two. Serious complications, such as infection, excessive bleeding, or feeling faint, are rare, but you should contact your healthcare provider if you notice ongoing pain, swelling, or signs of infection.

OCT is considered very safe with no known risks. The procedure does not involve radiation (like X-rays) and uses only light waves. Some people may experience mild eye discomfort from keeping their eyes open, but this is temporary.