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Optical Coherence Tomography (OCT) Measurement of Retinal Nerve Fiber Layer Thickness at the 7 O'Clock Position in the Left Eye

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

This test measures the thickness of the retinal nerve fiber layer, the bundle of nerve fibers that carries visual signals from your retina to your brain, at the 7 o'clock position of your left eye. Using optical coherence tomography (OCT) imaging, your doctor can detect early signs of glaucoma or optic nerve damage before vision loss occurs.

Quick summary

{"Uses OCT technology to capture detailed cross-sectional images of the retina","Measures the thickness of the nerve fiber layer to detect early glaucomatous damage","A non-invasive, painless eye examination that takes only a few minutes","Results help your eye doctor monitor eye health and detect vision problems early","No special preparation or eye drops are typically required before the test"}

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

Key facts at a glance

LOINC
86299-5
Short code
RNFL L7 OCT
Synonyms
L ret RNFL 7 o'clock thickness OCT
Category
cardiac
Sample
serum
Container
Not applicable - Imaging study
Units
N/A
Ref low
71
Ref high
140
Critical range
— – 10000 N/A
Fasting
false
Population
adult
Sex
all
Age range
≥ 18 years
Method
Optical Coherence Tomography (OCT)
CPT
92133
SNOMED
397540003
Specimen volume
Not applicable - Non-invasive imaging
Stability
Not applicable - Imaging study
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
1–24 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 (7 o'clock position) in your left eye. OCT is an advanced imaging technology that uses light waves to create detailed cross-sectional images of the retina, similar to how ultrasound uses sound waves.

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 align the machine with your eye. You will need to focus on a target light while the scanner painlessly captures images of your retina. The entire procedure takes only a few minutes and requires no special preparation.

Why is this test important?

The retinal nerve fiber layer contains the nerve fibers that carry visual information from the retina to the brain. Measuring its thickness helps doctors detect early signs of glaucoma, optic nerve damage, or other neurological conditions that may affect vision.

Reference range

Normal retinal nerve fiber layer (RNFL) thickness at clock hour 7 ranges approximately 71-140 micrometers in healthy adults. Thickness values are interpreted in conjunction with the overall RNFL circumference analysis and compared to age-matched normative database.N/A

Specimen: serum

Patient should remove contact lenses if worn. Pupil dilation may be performed to enhance imaging quality, though newer spectral-domain OCT systems often allow undilated imaging. Instruct patient to remain still and focus on fixation target during scan acquisition.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings2

Frequently asked questions

Does the test hurt?
No, OCT is a completely painless and non-invasive procedure. You may experience mild discomfort from keeping your eye still, but there is no pain or physical contact with the eye.
Do I need to fast before the test?
No special preparation is needed. You can eat and drink normally before the test. However, avoid wearing eye makeup on the day of the examination.
How long does it take to get results?
The imaging itself takes only a few minutes. Your doctor will typically discuss the results with you during a follow-up appointment, usually within a week.
How often should this test be repeated?
The frequency depends on your eye condition and your doctor's recommendations. For glaucoma monitoring, the test may be repeated annually or more frequently if there are concerns about disease progression.
  1. 1
    American Academy of Ophthalmology - OCT for GlaucomaSource
  2. 2
    National Eye Institute - GlaucomaSource

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