Left Retina Retinal Nerve Fiber Layer (RNFL) Thickness Test, Clock Hour 6, by Optical Coherence Tomography (OCT)
A non-invasive imaging test that uses safe, low-intensity light waves to measure the thickness of the retinal nerve fiber layer at clock hour 6 in your left eye, helping your eye doctor evaluate the health of the optic nerve and detect early signs of glaucoma, optic neuritis, or other conditions that may affect your vision.
{"Uses light waves to create detailed cross-sectional images of the retina","Helps detect and monitor glaucoma and other optic nerve diseases","The test is quick, painless, and requires no blood sample","Measures thickness at specific clock hours around the optic disc","Results help doctors track changes in eye health over time"}
Key facts at a glance
- LOINC
- 86298-7
- Short code
- RNFL-L-6
- Synonyms
- L ret RNFL 6 o'clock thickness OCT
- Category
- cardiac
- Sample
- serum
- Container
- N/A - This is an imaging test not requiring specimen collection
- Units
- N/A
- Ref low
- 100
- Ref high
- 140
- Critical range
- — – 10000 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- Optical Coherence Tomography (OCT)
- CPT
- 92134
- SNOMED
- 373741007
- Specimen volume
- N/A - Imaging study
- Stability
- N/A - Imaging study
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–48 hours
- Order
- routine
What is this test?
The Left Retina Retinal Nerve Fiber Layer (RNFL) thickness test by OCT is a specialized imaging procedure that measures the thickness of the nerve fiber layer surrounding the optic nerve in your left eye. Optical Coherence Tomography (OCT) uses light waves to capture detailed cross-sectional images of the retina, similar to how ultrasound uses sound waves. This test focuses specifically on clock hour 6, which corresponds to the inferior portion of the optic nerve.
How is the test performed?
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 machine scans your eye. The process is completely painless and takes only a few minutes. No eye drops or blood samples are required. The device uses low-intensity light to create high-resolution images of your retinal layers.
Why is it important?
The retinal nerve fiber layer consists of nerve fibers that carry visual information from the retina to the brain. Measuring its thickness helps doctors detect early changes that may indicate glaucoma, optic neuritis, or other conditions affecting the optic nerve. Comparing results over time helps track disease progression or treatment effectiveness.
Reference range
Normal Retinal Nerve Fiber Layer (RNFL) thickness at clock hour 6 (inferior temporal) typically ranges from 100-140 micrometers (μm). Values below 100 μm suggest focal RNFL thinning which may indicate glaucomatous or neurologic damage.N/A
Patient should remove contact lenses prior to imaging. Pupillary dilation may be performed for better visualization but is not always required. Patient should be informed that the test involves bright light exposure and should avoid rubbing eyes immediately before the scan.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test is primarily used for detecting and monitoring glaucoma, a condition that damages the optic nerve and can lead to vision loss if untreated. Thinning of the retinal nerve fiber layer, particularly at clock hour 6 (the inferior quadrant), may indicate glaucomatous damage. The test also helps differentiate between various optic nerve disorders and can detect damage from conditions like optic neuritis, ischemic optic neuropathy, or toxic/nutritional optic neuropathies. Early detection allows for timely intervention to preserve vision.
Frequently asked questions
Does the test hurt?
How long does the test take?
Do I need to prepare for the test?
When will I get my results?
How often should I have this test?
Sources
- 1
- 2
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
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