Understanding Your Diagnostic Test: Purpose, Procedure, and What Your Results May Mean for Your Care
This test uses optical coherence tomography (OCT) to measure the thickness of the retinal nerve fiber layer in your right eye at the 11 o'clock position, helping detect eye conditions like glaucoma.
{"Uses painless light waves to create detailed images of your eye's internal structures","Measures the thickness of the nerve layer that carries vision signals to your brain","Helps detect early signs of glaucoma and other optic nerve diseases","Takes only a few minutes with no discomfort","Regular testing helps track changes in your eye health over time"}
Key facts at a glance
- LOINC
- 86315-9
- Short code
- RNFL-R-11-OCT
- Synonyms
- R ret RNFL 11 o'clock thickness OCT
- Category
- cardiac
- Sample
- serum
- Container
- N/A - Imaging test
- Units
- N/A
- Ref low
- 46
- Ref high
- 102
- Critical range
- 40 N/A – 10000 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- Optical Coherence Tomography (OCT)
- CPT
- 92134
- SNOMED
- 371632002
- Specimen volume
- N/A - Non-invasive imaging procedure
- Stability
- N/A - Imaging performed at time of collection
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 1–24 hours
- Order
- routine
What is this test? This diagnostic test evaluates a sample from your body to look for information that can help your healthcare professional assess your health, identify possible conditions, or monitor an ongoing concern.
The Retinal Nerve Fiber Layer (RNFL) thickness test is an imaging procedure that uses Optical Coherence Tomography (OCT) to measure how thick the nerve fiber layer is in your right eye. The retina is the light-sensitive tissue at the back of your eye, and the retinal nerve fiber layer contains the nerves that send visual information to your brain. This test focuses specifically on the 11 o'clock position of your eye, which is one of the key areas doctors examine for early signs of damage.
Why is this test performed? Your healthcare professional may order this test to investigate symptoms, confirm or rule out a medical condition, guide treatment decisions, or check how well your body is responding to treatment over time.
Doctors order this test primarily to screen for and monitor glaucoma, a condition that damages the optic nerve. It can also help detect other conditions that affect the optic nerve, such as multiple sclerosis, optic neuritis, or ischemic optic neuropathy. The test is particularly useful because it can identify damage before you notice any vision loss, allowing for earlier treatment.
How is the test performed? Depending on the type of test, a healthcare professional may collect blood, urine, saliva, tissue, or another sample, or perform an imaging or measurement procedure; you will receive instructions about preparation and what to expect.
During the test, you will sit in front of the OCT machine and rest your chin on a support. The technician will ask you to look at a specific target while the device scans your eye using harmless light waves. The process is completely painless and takes only a few minutes. You may experience a brief flash of light, but there is no discomfort. No eye drops or injections are required, and you can return to your normal activities immediately after the test.
Understanding your results: Results are interpreted using the test method, reference ranges, your medical history, and other findings. An abnormal result does not always indicate disease, so discuss the meaning of your results and recommended next steps with your healthcare professional.
Your doctor will compare your RNFL thickness measurements to normal values based on age and ethnicity. Thinner than average measurements may indicate early nerve damage, while thicker measurements are generally not a concern. It's important to note that RNFL thickness can vary naturally between individuals, so your doctor will look at the overall pattern and track changes over time rather than focusing on a single measurement.
Reference range
Normal Retinal Nerve Fiber Layer (RNFL) thickness at clock hour 11 ranges from 46-102 μm. Values below 46 μm may indicate RNFL thinning suggestive of glaucomatous damage or optic neuropathy. Reference ranges vary by instrument manufacturer and patient demographics.N/A
No special preparation required. Patients should remove eye makeup and contact lenses prior to imaging. Pupillary dilation may be performed if necessary for optimal imaging quality. Inform technician of any eye surgery history or current eye conditions.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The RNFL thickness test is crucial for detecting glaucoma at its earliest stages, when treatment is most effective. Glaucoma is often called the 'silent thief of sight' because it typically causes no symptoms until significant vision loss has occurred. Regular RNFL testing allows your eye doctor to monitor the health of your optic nerve and intervene early if needed. This test is also valuable for tracking disease progression and evaluating how well treatments are working.
Results from this test are typically interpreted alongside other eye exams, including visual field testing and intraocular pressure measurements, to provide a complete picture of your eye health. If abnormal thinning is detected, your doctor may recommend more frequent monitoring or begin treatment to prevent further vision loss.
Frequently asked questions
Does the test hurt?
How long does the test take?
Do I need to do anything special to prepare?
When will I get my results?
How often should I have this test?
Sources
- 1
- 2
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy