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Optic Nerve Health

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Eye imaging explained

OCT, OCT angiography, and retinal photography with autofluorescence, and why tracking over time matters

Reviewed by Dr. James Deom, OD, MPH, FAAO, FSLS, Chief of Eye Care Services, Hazleton Eye Specialists Last reviewed: November 12, 2026 Audience: Patients & public, with a clinician section

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These three tests take pictures of the back of your eye, including the optic nerve head (the optic disc). None of them touches your eye or uses a needle, and each scan usually takes a few minutes.¹ Their biggest strength is comparison: a scan taken today becomes the baseline that later scans are measured against.

Schematic side view of an eye showing the cornea, lens, vitreous gel, retina along the back wall, the macula, and the optic nerve head where the optic nerve leaves the eye. Callouts: at the optic nerve head, OCT measures nerve fiber layer thickness and swelling, OCTA maps capillaries, and photos and autofluorescence show color, pallor, hemorrhages, and drusen; at the macula, OCT measures the ganglion cell layer and OCTA maps vessels.
Where each test looks. Fundus photos and autofluorescence give a flat surface picture; OCT gives cross-section slices; OCTA maps blood flow without dye. Original schematic, not to scale.

For patients and families

OCT (optical coherence tomography)

What it is: a scan that uses light waves to make cross-section pictures of the retina and optic nerve, a little like an ultrasound but with light.¹ ² You rest your chin on a support and look at a target. Nothing touches your eye.¹

What it shows at the optic nerve: the thickness of the nerve fiber layer (RNFL) around the disc and the ganglion cell layer (GCL) near the center of vision. These are the layers that thin when optic nerve fibers are lost. OCT can also show swelling of the optic nerve.³ ⁴

Stacked horizontal bands representing retinal layers from top to bottom: vitreous, retinal nerve fiber layer (highlighted navy), ganglion cell layer (highlighted), inner plexiform, inner nuclear, outer plexiform, outer nuclear, photoreceptors, retinal pigment epithelium, and choroid. An inset shows a dashed circle around the optic disc, the ring scan path where RNFL thickness is measured.
OCT shows the retina in cross-section. The RNFL and GCL are the layers most used to follow the optic nerve. Original schematic; layer thicknesses not drawn to proportion.

OCT angiography (OCTA)

What it is: the same kind of machine takes repeated scans of the same spot and detects moving blood cells, building a map of the tiny blood vessels. It does not need a dye injection.¹ ⁵

What it shows at the optic nerve: the network of small capillaries around the disc. Areas where those vessels look sparse are called reduced density or “dropout.”⁵ ⁶

Two schematic drawings of the optic disc on a black background with white radial capillaries. Left: a dense, even capillary network. Right: the same network with a dashed upper sector where capillaries are sparse, labeled reduced capillary density or dropout. Labeled as a drawing, not a patient scan.
Schematic drawing, not a patient scan. OCTA maps the small vessels around the disc; vessel density can be compared over time. Its role in acute NAION is still being studied.

Retinal (fundus) photography and autofluorescence

What it is: color photographs of the back of the eye. Autofluorescence uses a special light and filter to record the natural glow of some tissues. You see a bright flash; no dye is used.

What it shows at the optic nerve: the disc’s color (paleness, called pallor, can follow nerve damage), its edges (blurred edges can mean swelling), small hemorrhages, and, with autofluorescence, optic disc drusen near the surface, which can glow.⁷

Why follow-up scans matter most

One scan shows how your eye looks today. A series of scans shows whether anything is changing. Measurements naturally vary a little from visit to visit, so doctors look for change that is bigger than that normal variation, and for a steady trend across several visits.⁸ ⁹

Two schematic line charts labeled illustrative, not patient data, with no numeric values. Panel A: RNFL thickness declines gradually across six visits, starting inside a shaded band for expected test-retest variability and moving below it. Panel B: after NAION, thickness rises sharply at onset from swelling, then falls over 1, 3, 6, and 12 months to below the pre-event level, approaching a dashed measurement floor.
Illustrative, not patient data. A baseline makes change easier to judge. After NAION, early swelling is followed by thinning over months.

After NAION, for example, the nerve first swells and then thins over the following months.³ ⁴ Having a scan from before any problem gives your doctors a personal reference point, instead of comparing you only with averages.

What these tests cannot do: they do not predict or prevent NAION or other sudden problems. If you ever have sudden vision loss, get same-day care.

Dr. Deom’s recommendation (clinical opinion / practice recommendation)

Dr. James Deom recommends that everyone starting or taking a GLP-1 medication have a comprehensive dilated eye exam with OCT, OCT angiography (OCTA), and retinal photography (fundus photos with autofluorescence) as a baseline and for follow-up, and seek same-day care for sudden vision loss.

This is his clinical opinion, not a formal rule from every professional group. AAO and NANOS do not recommend an eye exam only to predict NAION, and no test can reliably predict or prevent it.

Choosing an eye doctor (Dr. Deom’s opinion): In Dr. Deom’s opinion, the eye doctor and office you choose should have the technology to assess you and follow you over time, including OCT, OCT angiography (OCTA), and retinal photography with autofluorescence. Follow-up scans are most useful on the same type of device, so measurements can be compared directly.

Dr. James Deom’s personal clinical thought

This is his opinion, not established evidence. It is not a finding from the studies or a position of the FDA, EMA, AAO, NANOS, or AOA.

As people lose weight and get healthier on GLP-1 medicines, their blood pressure and cholesterol medicines are often not reviewed or adjusted. Blood pressure treatment that is no longer matched to a person’s needs may lead to low blood pressure (hypotension). Low blood pressure can be more pronounced at night and could reduce blood flow to the optic nerve during sleep. That possibility would fit the typical way NAION presents: vision loss noticed on waking.

Dr. Deom recommends that people taking a GLP-1 medicine also work on exercise and diet, and keep regular visits with their usual doctors — even if that doctor did not prescribe the GLP-1 — so the rest of their care, including blood pressure, is maintained. Do not start, stop, or change a blood pressure or cholesterol medicine on your own; talk with the clinician who prescribes it.

Summary table

Test How it is done What it shows at the optic nerve head Value for tracking over time Main limits
OCT Non-contact light scan; a few minutes;¹ dilation sometimes RNFL and GCL thickness; disc swelling Event and trend analysis against test-retest variability;⁸ ⁹ documents swelling resolving into thinning³ ⁴ Floor effect in advanced loss;¹⁰ segmentation errors and artifacts;¹¹ signal quality; device-specific values
OCTA Repeated OCT scans of one area; no dye¹ ⁵ Peripapillary and disc capillary density; sectoral dropout Vessel density can be compared across visits on the same device⁵ Motion and projection artifacts; signal quality;⁵ ¹² role in acute NAION still being studied⁶ ¹³ ¹⁴
Fundus photos Bright flash; no dye Disc color, pallor, edges, hemorrhages, cup Side-by-side visual comparison; documents pallor developing Qualitative; depends on image quality and pupil size
Autofluorescence Filtered flash; no dye Superficial optic disc drusen⁷ Records drusen for future comparison Buried drusen may not show; EDI-OCT is more sensitive⁷

For clinicians

OCT at the ONH

  • Parameters: peripapillary RNFL (global and sectoral), macular GCL/GCIPL, and ONH metrics. In NAION, the RNFL is markedly thickened acutely and thins over months; in one Stratus OCT cohort, RNFL loss at 3, 6, and 12 months was about 39%, 42%, and 44%.³ GCIPL thinning was detectable at 1 month in a spectral-domain study, earlier than RNFL thinning, which is masked by edema.⁴ GCIPL is therefore useful during the edematous phase.
  • Distinguishing edema from atrophy: serial RNFL alone can show an apparent “normalization” as edema resolves into atrophy; pair it with GCIPL and disc photos.³ ⁴

Tracking: event versus trend analysis

  • Event analysis flags a follow-up value that differs from baseline by more than test-retest variability. Trend analysis estimates a rate of change by regression across visits.⁸ ⁹
  • In one Cirrus study of glaucomatous eyes, the intervisit tolerance limit for average RNFL thickness was 3.89 µm; change beyond the device’s test-retest limits is more likely to be real.⁸ Values are device-specific and not interchangeable across platforms.
  • Obtain two reliable baselines where possible, use the same device and scan protocol, and review the raw scans, not just the printout.

Limits

  • Floor effect: RNFL stops thinning at a residual thickness despite further functional loss, which limits tracking in advanced disease; the floor and dynamic range differ by device.¹⁰ GCIPL and visual fields remain important.
  • Segmentation errors and artifacts: common in RNFL and macular scans and can produce false progression or mask it.¹¹ Disc edema, high myopia, epiretinal membrane, and media opacity increase risk.
  • Signal quality: low signal strength reduces RNFL values; document signal quality and repeat poor scans.
  • OCTA: motion and projection artifacts, segmentation of the peripapillary slab, and device-specific density metrics.⁵ ¹² In NAION, reduced peripapillary vessel density has been reported and associated with RNFL thinning and field loss.⁶ In acute disease, small case series describe sectoral capillary reduction,¹³ ¹⁴ but edema confounds measurements and the use of OCTA in acute NAION is an evolving area of research, not a validated diagnostic or prognostic test.

Photos and autofluorescence

  • Color photos document disc edema, hemorrhages, pallor (sectoral or diffuse), and cupping. FAF detects superficial drusen; per the ODDS Consortium, EDI-OCT is the preferred method for diagnosing drusen, including buried drusen.⁷

In practice

Dr. Deom’s recommendation above applies; his framework for baseline and follow-up intervals is in the monitoring framework.

How to reach us

Same-day evaluation: providers can call the office at 570-453-2020 (fax 570-453-1020), or refer a patient or ask a question by email. Patients can schedule an exam online.

For privacy, please don’t include patient names or other identifying details in email. Our team will call to schedule and gather details securely.

General contact and referrals: Hazleton Eye Specialists, phone 570-453-2020, fax 570-453-1020. See Referral information for what to send.

References

  1. American Academy of Ophthalmology. What Is Optical Coherence Tomography? (covers OCT and OCTA; published Aug 13, 2026). https://www.aao.org/eye-health/treatments/what-is-optical-coherence-tomography
  2. Huang D, et al. Optical coherence tomography. Science. 1991;254(5035):1178-1181. https://pubmed.ncbi.nlm.nih.gov/1957169/
  3. Contreras I, et al. Follow-up of nonarteritic anterior ischemic optic neuropathy with optical coherence tomography. Ophthalmology. 2007;114(12):2338-2344. https://pubmed.ncbi.nlm.nih.gov/17719640/
  4. Akbari M, et al. Retinal ganglion cell loss precedes retinal nerve fiber thinning in nonarteritic anterior ischemic optic neuropathy. J Neuroophthalmol. 2016;36(2):141-146. https://pubmed.ncbi.nlm.nih.gov/26835663/
  5. Kashani AH, et al. Optical coherence tomography angiography: a comprehensive review of current methods and clinical applications. Prog Retin Eye Res. 2017;60:66-100. https://pubmed.ncbi.nlm.nih.gov/28760677/
  6. Hata M, et al. Structural and functional analyses in nonarteritic anterior ischemic optic neuropathy: optical coherence tomography angiography study. J Neuroophthalmol. 2017;37(2):140-148. https://pubmed.ncbi.nlm.nih.gov/27984351/
  7. Malmqvist L, et al. The Optic Disc Drusen Studies Consortium recommendations for diagnosis of optic disc drusen using optical coherence tomography. J Neuroophthalmol. 2018;38(3):299-307. https://pubmed.ncbi.nlm.nih.gov/29095768/
  8. Mwanza JC, et al. Reproducibility of peripapillary retinal nerve fiber layer thickness and optic nerve head parameters measured with Cirrus HD-OCT in glaucomatous eyes. Invest Ophthalmol Vis Sci. 2010;51(11):5724-5730. https://pubmed.ncbi.nlm.nih.gov/20574014/
  9. Leung CK, et al. Evaluation of retinal nerve fiber layer progression in glaucoma: a study on optical coherence tomography guided progression analysis. Invest Ophthalmol Vis Sci. 2010;51(1):217-222. https://pubmed.ncbi.nlm.nih.gov/19684001/
  10. Mwanza JC, et al. Residual and dynamic range of retinal nerve fiber layer thickness in glaucoma: comparison of three OCT platforms. Invest Ophthalmol Vis Sci. 2015;56(11):6344-6351. https://pubmed.ncbi.nlm.nih.gov/26436887/
  11. Li A, et al. Impact of artifacts from optical coherence tomography retinal nerve fiber layer and macula scans on detection of glaucoma progression. Am J Ophthalmol. 2021;221:235-245. https://pubmed.ncbi.nlm.nih.gov/32818450/
  12. Spaide RF, et al. Optical coherence tomography angiography. Prog Retin Eye Res. 2018;64:1-55. https://pubmed.ncbi.nlm.nih.gov/29229445/
  13. Balducci N, et al. Optical coherence tomography angiography in acute arteritic and non-arteritic anterior ischemic optic neuropathy. Graefes Arch Clin Exp Ophthalmol. 2017;255(11):2255-2261. https://pubmed.ncbi.nlm.nih.gov/28861697/
  14. Wright Mayes E, et al. Optical coherence tomography angiography in nonarteritic anterior ischemic optic neuropathy. J Neuroophthalmol. 2017;37(4):358-364. https://pubmed.ncbi.nlm.nih.gov/28301863/

All diagrams on this page are original schematics created for this site. They are not patient scans or patient data.

Medical disclaimer. This page is for general education. The patient section is not medical advice, and the clinician section is not a clinical practice guideline; neither replaces an examination, clinical judgment, or specialty consultation. If you have sudden vision loss, seek same-day care from an eye doctor or an emergency department. Information is current as of the “last reviewed” date.