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OCT Retinal Nerve Fiber Layer Thickness Test – Left Eye, 9 O'Clock Position

Published: August 9, 2026Updated: August 17, 2026

This test measures the thickness of the retinal nerve fiber layer at the 9 o'clock position of the left eye using OCT imaging, helping your doctor detect and monitor optic nerve damage from conditions such as glaucoma.

Quick summary

{"Non-invasive eye scan using light waves","Measures nerve fiber layer thickness to detect glaucoma damage","Quick and painless procedure lasting a few minutes","Results help monitor eye health over time","Early detection of nerve damage is crucial for vision preservation"}

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
86286-2
Short code
RNFL-L-CH9-OCT
Synonyms
L ret RNFL 9 o'clock thickness OCT
Category
cardiac
Sample
serum
Container
Not applicable - this is an imaging test not requiring specimen collection
Units
N/A
Ref low
50
Ref high
80
Critical range
— – 10000 N/A
Fasting
false
Population
adult
Sex
all
Age range
≥ 18 years
Method
Optical Coherence Tomography (OCT) - Spectral Domain OCT (SD-OCT)
CPT
92134 - Scanning computerized ophthalmic diagnostic testing, retina
SNOMED
371632002
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) to measure the thickness of the retinal nerve fiber layer (RNFL) at a specific location in your left eye – the 9 o'clock position (which corresponds to the nasal side of the eye). The retinal nerve fiber layer 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 an OCT machine and rest your chin on a support. The machine will scan your eye using light waves to create detailed cross-sectional images. You will need to keep your eyes open and focused on a target. The procedure is quick, painless, and does not require any injections or eye drops. No special preparation is needed before the test.

Why is this test important?

Measuring RNFL thickness helps doctors detect and monitor damage to the optic nerve, which is commonly caused by glaucoma. By checking specific clock hours, doctors can identify which areas of the nerve are affected and track changes over time. Early detection of RNFL thinning can lead to timely treatment to prevent further vision loss.

What do the results mean?

Your doctor will compare your results with normal values based on age and other factors. Thinner than average RNFL at the 9 o'clock position may indicate nerve damage, while normal thickness suggests healthy nerve tissue. Your doctor will interpret the results in combination with other eye examinations to make a complete assessment of your eye health.

Reference range

Normal RNFL thickness at clock hour 9 (temporal quadrant) ranges from approximately 50-80 microns in healthy adults. Reference ranges vary by instrument manufacturer and population norms.N/A

Specimen: serum

Patient should remove contact lenses if applicable. Pupils may need to be dilated for optimal imaging. Inform technician of any eye surgery history, glaucoma, or optic nerve conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Frequently asked questions

Does the OCT scan hurt?
No, the OCT scan is completely painless. It uses light waves to create images, not radiation. You may feel slight discomfort from keeping your eyes open, but the procedure is generally very comfortable.
How long does the test take?
The actual scanning process takes only a few seconds to a minute per eye. The entire appointment, including preparation and explanation, typically takes about 10-15 minutes.
Do I need to do anything special to prepare for the test?
No special preparation is needed. You can eat and drink normally before the test. If you wear contact lenses, you may be asked to remove them before the scan. Bring your glasses if you have them.
How often should this test be repeated?
The frequency depends on your eye condition. For glaucoma patients, OCT scans are typically repeated every 6-12 months to monitor changes. Your doctor will determine the appropriate schedule based on your individual situation.
Can this test detect other eye conditions?
While primarily used for glaucoma monitoring, OCT RNFL measurements can also help in assessing other optic nerve conditions such as optic neuritis, ischemic optic neuropathy, and certain neurological disorders that may affect the optic nerve.
  1. 1
    American Academy of Ophthalmology - OCT for GlaucomaSource
  2. 2
    National Eye Institute - Glaucoma InformationSource

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.

Medical Disclaimer

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