Left Retina Retinal Nerve Fiber Layer (RNFL) Thickness Test (OCT)
Optical coherence tomography (OCT) is a non-invasive eye imaging test that measures the thickness of the nerve fiber layer in your left retina, helping your eye doctor detect early signs of glaucoma, optic nerve damage, and other conditions before vision loss occurs.
{"Uses light waves to create detailed images of your retina's nerve layer","Helps detect glaucoma and other optic nerve conditions early","The test is quick, painless, and requires no needles or blood samples","Results help doctors monitor eye health over time","Your eyes may be dilated for better imaging"}
Key facts at a glance
- LOINC
- 86288-8
- Short code
- RNFL inferior L
- Synonyms
- L ret RNFL inf thickness OCT
- Category
- cardiac
- Sample
- serum
- Container
- Not applicable (imaging study, not a blood test)
- Units
- N/A
- Ref low
- 100
- Ref high
- 160
- Critical range
- — – 10000 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- Optical Coherence Tomography (OCT)
- CPT
- 92134
- SNOMED
- 421531009
- Specimen volume
- Not applicable (imaging study)
- Stability
- Not applicable (imaging study)
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
What is this test?
The Left Retina Retinal Nerve Fiber Layer (RNFL) Thickness test uses a special imaging technology called Optical Coherence Tomography (OCT). It measures how thick the nerve fiber layer is in the inferior (lower) portion of your left retina. This 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 device will scan your eye using harmless light waves. The process takes only a few minutes and is completely painless. Your doctor may use eye drops to dilate your pupils for clearer images.
Why is this test important?
Measuring RNFL thickness helps doctors detect changes in the optic nerve before vision loss occurs. Thinning of the RNFL can be an early sign of glaucoma, optic neuritis, or other neurological conditions. Early detection allows for prompt treatment to prevent further damage.
How to prepare
No special preparation is needed. If your eyes will be dilated, bring sunglasses as your vision may be temporarily blurred and your eyes may be sensitive to light. Remove eye makeup before the test. Continue taking your regular medications unless your doctor instructs otherwise.
Reference range
Normal inferior retinal nerve fiber layer (RNFL) thickness: 100-160 micrometers (µm). Values may vary by instrument manufacturer and population. Thinning may indicate glaucomatous or optic nerve damage.N/A
Patient should remove contact lenses if applicable. Pupillary dilation may be performed for better imaging. No special preparation required. Inform technician of any eye surgery history or retinal conditions.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The RNFL thickness measurement is primarily used for detecting and monitoring glaucoma, a condition that damages the optic nerve. Thinner than normal RNFL in the inferior quadrant may indicate early glaucoma damage. The test is also valuable for tracking disease progression and evaluating treatment effectiveness. Additionally, abnormalities in RNFL thickness can signal neurological conditions such as multiple sclerosis or optic neuropathy.
Frequently asked questions
Does the test hurt?
How long does the test take?
Will I need someone to drive me home?
How often should I have this test?
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