Optical Coherence Tomography (OCT) of the Retinal Nerve Fiber Layer, Clock Hour 10, Left Eye
This test uses optical coherence tomography (OCT) to measure the thickness of the retinal nerve fiber layer at a specific location (clock hour 10) on the left eye. The retinal nerve fiber layer contains nerve fibers that carry visual information from the retina to the brain. Measuring its thickness helps your doctor evaluate the health of the optic nerve, detect early signs of glaucoma, monitor disease progression, and assess how well your treatment is working.
{"Measures retinal nerve fiber layer thickness at clock hour 10","Helps detect and monitor glaucoma and optic nerve damage","Non-invasive imaging test using light waves","Results help doctors assess eye health and disease progression","Performed by scanning the retina with specialized equipment"}
Key facts at a glance
- LOINC
- 86302-7
- Short code
- RNFL L clock 10 OCT
- Synonyms
- L ret RNFL 10 o'clock thickness OCT
- Category
- cardiac
- Sample
- serum
- Container
- Not applicable - This is an imaging procedure, not a blood or fluid specimen.
- Units
- N/A
- Ref low
- 70
- Ref high
- 120
- Critical range
- — – 10000 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- Optical Coherence Tomography (OCT)
- CPT
- 92133
- SNOMED
- 397489006
- Specimen volume
- Not applicable
- Stability
- Not applicable
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
What is this test?
This test uses Optical Coherence Tomography (OCT) to measure the thickness of the retinal nerve fiber layer (RNFL) at a specific point (clock hour 10) on the left retina. The retinal nerve fiber layer contains nerve fibers that carry visual information from the retina to the brain. Measuring its thickness helps doctors evaluate the health of the optic nerve and detect early changes that may indicate eye diseases.
Why is this test performed?
This test is primarily performed to detect and monitor glaucoma, as thinning of the retinal nerve fiber layer is a key indicator of glaucoma damage. It may also be used to evaluate other optic nerve conditions, monitor disease progression, and assess treatment effectiveness. The test provides detailed cross-sectional images of the retina that cannot be obtained through regular eye exams.
How is the test done?
During the test, you will sit in front of an OCT machine and place your chin on a support. The technician will ask you to look at a target light while the scanner takes images of your eye. The process is quick, painless, and does not involve any radiation or physical contact with your eye. The entire procedure typically takes about 10-15 minutes.
Are there any risks?
OCT is a very safe procedure with no known risks. It uses light waves to create images, not radiation. Some patients may experience mild eye strain or difficulty keeping still during the scan, but these are minor and temporary. No special preparation is needed before the test.
Reference range
Retinal nerve fiber layer thickness at clock hour 10 typically ranges from 70-120 microns in healthy adults. Reference ranges may vary by instrument manufacturer and population norms.N/A
Patient should remove contact lenses before imaging. Pupil dilation may be performed for better visualization. Avoid eye makeup or creams around the eyes prior to examination. Inform technician of any eye surgeries, glaucoma, or optic nerve disorders.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Frequently asked questions
Do I need to fast before this test?
Will the test hurt?
How long does it take to get results?
Do I need to stop taking my eye medications before the test?
Can I drive after the 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