Left Retina RNFL Thickness Test (OCT)
This non-invasive eye test uses optical coherence tomography to measure the thickness of the retinal nerve fiber layer in the upper portion of your left eye, helping your doctor detect early optic nerve damage and monitor glaucoma.
{"Measures retinal nerve fiber layer thickness at the 12 o'clock position of the left eye","Uses OCT technology for detailed eye tissue imaging","Helps diagnose and monitor glaucoma and other optic nerve conditions","Non-invasive procedure taking about 5-10 minutes","Results help doctors assess optic nerve health"}
Key facts at a glance
- LOINC
- 86292-0
- Short code
- RNFL CH12 OCT
- Synonyms
- L ret RNFL 12 o'clock thickness OCT
- Category
- cardiac
- Sample
- serum
- Container
- Not applicable - this is an imaging test, not a blood test
- 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
- 422148006
- Specimen volume
- Not applicable - imaging study
- Stability
- Not applicable
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 1–24 hours
- Order
- routine
What is this test?
The Left Retina RNFL Thickness Test (OCT) is an advanced imaging test that measures the thickness of the retinal nerve fiber layer in your left eye. Specifically, it measures the 12 o'clock position, which corresponds to the upper portion of your retina. The test uses Optical Coherence Tomography (OCT), a non-invasive imaging technology that creates detailed cross-sectional images of your retina and optic nerve.
How is the test performed?
During the test, you will sit in front of an OCT machine. You will place your chin on a support and look at a specific target. The device will scan your eye without touching it. The test is quick, comfortable, and takes about 5-10 minutes. No eye drops or injections are required.
Why is this test important?
Measuring the RNFL thickness helps doctors detect early damage to the optic nerve, which is crucial for diagnosing and managing glaucoma. It also helps monitor disease progression and treatment effectiveness. A thinner than normal RNFL may indicate optic nerve damage.
What do the results mean?
Your doctor will compare your results to normal values based on age and other factors. A thinner RNFL at the 12 o'clock position may suggest early glaucomatous damage, while a thicker RNFL may indicate swelling or inflammation. Your doctor will interpret the results in context with other eye exam findings.
Reference range
Normal retinal nerve fiber layer (RNFL) thickness at clock hour 12 (superior quadrant) typically ranges from 100-140 micrometers. Values may vary by instrument manufacturer and patient age.N/A
Patient should remove contact lenses if applicable. Pupillary dilation may be performed for optimal imaging. No special fasting required. Inform technician of any eye surgery history or current eye conditions.
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. Early detection is crucial as glaucoma often progresses silently. The 12 o'clock position measurement is particularly important because it corresponds to the superior retinal nerve fiber layer, which is commonly affected in glaucoma. The test also helps differentiate between glaucoma and other optic nerve diseases, monitors treatment effectiveness, and tracks disease progression over time.
Frequently asked questions
Does the test hurt?
How long does the test take?
Do I need to prepare for the test?
How often should I have this test?
What happens if my results are abnormal?
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