Retinal Nerve Fiber Layer Thickness Measurement Using Optical Coherence Tomography (OCT), Clock Hour 1 Position, Left Eye
This test uses optical coherence tomography (OCT), a safe and painless imaging technology, to measure the thickness of the retinal nerve fiber layer (RNFL) at the clock hour 1 position on your left retina. This layer contains the nerve fibers that carry visual information from your eye to your brain. Measuring its thickness at this specific location helps your eye doctor evaluate the health of your optic nerve, because thinning can be an early sign of conditions such as glaucoma, often before you notice any vision changes. The scan uses light waves instead of radiation, requires no injections or blood samples, and takes only a few minutes to complete.
{"Measures retinal nerve fiber layer thickness at the 1 o'clock position of the left eye","Helps detect and monitor glaucoma and other optic nerve conditions","Non-invasive imaging test that takes only a few minutes","Results help doctors assess optic nerve health","Thinner RNFL may indicate nerve damage"}
Key facts at a glance
- LOINC
- 86293-8
- Short code
- RNFL-CH1-OCT
- Synonyms
- L ret RNFL 1 o'clock thickness OCT
- Category
- cardiac
- Sample
- serum
- Container
- Not applicable - imaging test
- Units
- N/A
- Ref low
- 75
- Ref high
- 120
- Critical range
- — – 10000 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- Optical Coherence Tomography (OCT)
- CPT
- 92134
- SNOMED
- 397540003
- Specimen volume
- Not applicable - imaging test
- Stability
- Not applicable - imaging test
- 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), a sophisticated imaging technology, to measure the thickness of the retinal nerve fiber layer (RNFL) at a specific location on your left retina. The 'clock hour 1' refers to the 1 o'clock position on the retina, which corresponds to a specific area of the optic nerve. The RNFL contains nerve fibers that carry visual information from your retina to your brain.
How is the test performed?
During the test, you will sit in front of the OCT machine and place your chin on a support. You will be asked to look at a target light while the scanner takes images of your retina. The test is completely painless, non-invasive, and does not require any injections or blood samples. The entire procedure takes about 5-10 minutes.
Why is this test important?
Measuring RNFL thickness helps your doctor evaluate the health of your optic nerve. Changes in RNFL thickness can occur before you notice any vision loss, making this test valuable for early detection of certain eye conditions. The test provides precise, objective measurements that can be compared over time to track disease progression or treatment effectiveness.
Reference range
Normal retinal nerve fiber layer thickness at clock hour 1 (temporal superior) typically ranges from 75-120 microns; reference ranges vary by instrument manufacturer and population normsN/A
Patient should remove contact lenses if applicable; pupil dilation may be performed for optimal imaging; avoid eye drops that may affect pupil size within 24 hours prior to testing
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test is primarily used to detect and monitor glaucoma, a condition that damages the optic nerve. It can also help evaluate other conditions that may affect the optic nerve, such as optic neuritis, multiple sclerosis-related optic neuropathy, or other neuro-ophthalmic disorders. A thinner-than-normal RNFL at the 1 o'clock position may indicate localized nerve fiber loss, while comparison with previous tests can reveal whether the condition is progressing.
Frequently asked questions
Do I need to fast before this test?
Will the test hurt?
How long does it take to get results?
Is this test safe?
What do abnormal results mean?
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