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Fundus photography is a critical clinical skill for ophthalmic assistants, providing objective, permanent documentation of posterior segment findings that can be compared over time. High-quality fundus photographs allow physicians to track disease progression, document the response to treatment, and communicate findings across providers. The COA exam tests knowledge of fundus camera equipment, patient preparation, imaging technique, stereo photography, optical coherence tomography (OCT), and the ophthalmic assistant's role in fluorescein angiography (FA).
Unlike direct ophthalmoscopy, which provides a dynamic view seen only by the examiner, fundus photography creates a permanent, shareable record. Digital photography has revolutionized retinal documentation — images can be instantly reviewed, compared side-by-side with previous visits, and shared electronically for specialist consultation. Artificial intelligence-based retinal analysis is increasingly applied to fundus photographs for diabetic retinopathy screening and glaucoma risk assessment.
This guide covers the complete fundus photography skill set for the COA exam: equipment types and their clinical applications, patient positioning and dilation, focusing technique for both disc-centered and macula-centered views, stereo disc photography, an overview of OCT, fluorescein angiography basics, image quality troubleshooting, and documentation standards.
Different clinical needs require different imaging systems. Understanding which camera is appropriate for which clinical situation is tested on the COA exam.
| Camera Type | Field of View | Dilation Required | Best Clinical Use |
|---|---|---|---|
| Standard fundus camera (30°) | 30° | Preferred | High-resolution disc and macula documentation |
| Standard fundus camera (45°) | 45° | Preferred; NM capable | Posterior pole + some mid-periphery; general screening |
| Non-mydriatic camera | 45°–60° | No (works in dark room) | Diabetic screening, telemedicine programs |
| Wide-field (e.g., Optos) | 200° (scanning laser) | Usually not required | Peripheral retina: DR, RD, lattice, tumors, uveitis |
| Ultra-widefield (UWF) | Up to 267° | Usually not required | Full peripheral survey; RD screening; retinal consultations |
| Stereo fundus camera | 30° | Required | Stereo disc photography; glaucoma nerve head assessment |
Non-Mydriatic vs. Mydriatic Photography
Non-mydriatic cameras use infrared light for focusing (invisible to the patient, so the pupil does not constrict) and brief white light flash for image capture. They require a minimum pupil size of approximately 3–4mm and a darkened room. While convenient, NM images are often noisier and have more artifact than dilated photographs. For definitive diagnosis and documentation in glaucoma monitoring, dilated photography is preferred. Many telemedicine diabetic retinopathy programs successfully use NM photography with protocols validated by the American Telemedicine Association.
Dilate both eyes
Tropicamide 1% ± phenylephrine 2.5%; wait 20–30 min for adequate dilation
Clean camera lens
Wipe external lens with lens paper; check for dust or smudges that will appear in images
Confirm camera settings
Flash intensity, field of view, image resolution, and patient file are set correctly
Enter patient information
Name, DOB, eye (OD/OS), date, and indication into the imaging system
Review for contraindications
Allergy to drops? Previous adverse reactions? Photosensitive medications?
Chin rest and forehead band
Lateral canthus aligned with the height mark on the upright. Forehead firmly against the band — loose positioning causes movement artifact.
Working distance
Camera approaches the eye from arm's length; final working distance of ~35–40mm depending on camera model. Too close = glare; too far = dark image.
Fixation target
Use external fixation targets to direct gaze for different retinal areas. Internal fixation light centers on the fovea. Ask patient to keep their eye open and not blink.
Eliminate lid artifacts
Ask patient to open their eye as wide as possible. Gently retract upper lid if lashes obscure the pupil. Lid speculum rarely needed but available.
Minimize blink reflex
Instruct patient: "Try not to blink — I'll take the picture quickly." Use the flash button immediately after a blink for best timing.
Proper focusing is the most technique-dependent step in fundus photography. Most modern fundus cameras use a split-line or dual-circle focusing target that aligns when the camera is correctly focused on the retina.
Red-Free (Green) Filter
Eliminates red wavelengths, enhancing contrast of blood vessels, nerve fiber layer, and hemorrhages (which appear dark). Excellent for:
Standard Color (White Flash)
Full-color photograph showing the fundus as seen clinically. Best for:
| Image | Center Point | Primary Purpose | Structures Shown |
|---|---|---|---|
| Disc-centered | Optic disc | Glaucoma monitoring, disc documentation | Optic nerve, NRR, cup, arcades, RNFL |
| Macula-centered | Fovea | AMD, diabetic maculopathy, macular hole | Macula, foveal reflex, drusen, exudates |
| Stereo disc pair | Optic disc (×2, offset 3°) | 3D optic nerve assessment, cup depth | Optic nerve head in stereoscopic depth |
| Superior peripheral | Superior retina | Lattice, peripheral breaks, detachment | Superior arcuate area, retinal periphery |
| Inferior peripheral | Inferior retina | Inferior lattice, peripheral pathology | Inferior arcuate area, retinal periphery |
Stereo optic disc photography captures two images from slightly different angles (approximately 3° apart) to create a three-dimensional view of the optic nerve head. This allows assessment of cup depth, disc elevation or cupping, and peripapillary changes that cannot be determined from a single flat photograph.
Stereo Photography Technique
Sequential Method (most common)
Quality Requirements
Optical coherence tomography (OCT) has become one of the most important diagnostic imaging technologies in ophthalmology. While COA candidates are not expected to interpret OCT findings at the expert level, understanding the technology, patient setup, and the clinical applications relevant to your role is tested.
What OCT Measures
OCT Patient Setup
| OCT Technology | Scanning Speed | Key Feature | Common Device |
|---|---|---|---|
| Time-domain OCT | ~400 A-scans/sec | Older; slower; limited resolution | Stratus OCT (legacy) |
| Spectral-domain (SD-OCT) | ~27,000 A-scans/sec | High resolution; fast; standard of care | Cirrus, Spectralis, Topcon DRI |
| Swept-source OCT | ~100,000 A-scans/sec | Deeper penetration (choroid); works through small pupils | Topcon Triton, Zeiss Plex Elite |
| OCT-Angiography (OCTA) | Varies | Non-invasive vascular flow mapping; no dye | Optovue AngioVue, Cirrus HD-OCT with AngioPlex |
Fluorescein angiography (FA) is a specialized diagnostic test where sodium fluorescein dye is injected intravenously and images of the fundus are taken in rapid sequence as the dye passes through the retinal and choroidal vasculature. It reveals vascular leakage, neovascularization, ischemia, and other abnormalities not visible on standard fundus photography.
Pre-Procedure
During Procedure
Post-Procedure Monitoring
Fluorescein Angiography Adverse Reaction Rates
~5%
Nausea / Vomiting
~0.5%
Urticaria / Hives
~1:200,000
Anaphylaxis (rare)
| Image Problem | Likely Cause | Solution |
|---|---|---|
| Central glare / bright artifact | Camera too close; corneal reflex; media opacity | Increase working distance; re-approach; tilt slightly |
| Blurry/unfocused image | Incorrect focus setting; patient movement | Re-adjust focus; remind patient to hold still; tighter chin rest |
| Dark/underexposed image | Small pupil; low flash power; media haze | Dilate; increase flash intensity; wait for better pupil |
| Washed-out/overexposed | Excessive flash; highly reflective fundus | Reduce flash power setting |
| Eyelash artifact (dark bars) | Lashes or lid edge in optical path | Gently retract lid; ask patient to open wide; lid speculum |
| Blurring from lens (posterior capsule) | Posterior capsule opacity (PCO) in pseudophakic eye | Note PCO grade; physician may proceed with YAG laser; reassess image after |
| Image in wrong location | Incorrect fixation target used or patient misunderstood | Re-instruct patient; verify fixation target is correct for intended view |
One of the most powerful uses of fundus photography is serial comparison — tracking how a patient's fundus changes over months and years. This requires consistent documentation standards.
Documentation Standards
Serial Comparison: What Physicians Look For
Practice COA Exam Questions on Retinal Imaging
Test your knowledge on fundus photography, OCT, fluorescein angiography, and all COA imaging and diagnostic topics.
Direct and indirect fundus examination, disc-cup ratio, and fundus abnormalities.
Automated perimetry, reliability indices, and glaucoma field defect patterns.
Anterior segment examination, illumination types, and slit lamp technique.
Complete COA certification guide: eligibility, exam format, and study strategy.
What types of retinal cameras are used in ophthalmic practice?
Fundus cameras vary by field of view and technology: (1) Standard non-mydriatic cameras: 30°–45° field of view; can image through undilated pupils (3mm or larger); most common in general practice. (2) Mydriatic cameras: wider field, require pupil dilation; better image quality. (3) Wide-field cameras (e.g., Optos Daytona, Optomap): 200° panoramic field using scanning laser; excellent for peripheral retinal examination; single-capture imaging. (4) Ultra-widefield systems: up to 267° with minimal or no dilation; increasingly used for diabetic retinopathy and retinal detachment screening.
Why is pupil dilation important for fundus photography?
Pupil dilation (mydriasis) significantly improves fundus image quality by allowing more light to enter the eye and providing a wider aperture for the camera. Undilated (non-mydriatic) photography can be performed through pupils of 3mm or larger, but quality is often reduced and peripheral retinal coverage is limited. For detailed disc photography, macula assessment, and peripheral examination, dilation to 6–8mm using tropicamide 1% (with or without phenylephrine 2.5%) is standard.
What is the difference between a macula-centered and a disc-centered fundus photograph?
A disc-centered (optic nerve head-centered) photograph places the optic disc in the center of the image, maximizing detail of the optic nerve head, cup-to-disc ratio, disc margins, and peripapillary retinal nerve fiber layer. A macula-centered photograph places the fovea in the center, optimizing visualization of the macula, foveal reflex, drusen, and macular pathology. Standard documentation of the posterior pole typically includes both disc-centered and macula-centered images for each eye.
What is the ophthalmic assistant's role in fluorescein angiography (FA)?
Ophthalmic assistants play a key supporting role in FA, which requires physician supervision. Responsibilities include: (1) Patient preparation — reviewing allergy history, obtaining informed consent, starting IV access if designated. (2) Equipment preparation — setting up the angiography system, checking exciter and barrier filters, calibrating timing. (3) During the procedure — monitoring the patient for adverse reactions (nausea, vomiting, hives, anaphylaxis), documenting injection time, communicating with the photographer (often a technician or physician). (4) Post-procedure — monitoring patient for 20–30 minutes, advising about yellow skin/urine discoloration for 24 hours, documenting any reactions. The assistant should know the signs of anaphylaxis and the emergency response protocol.
What are the most common causes of poor fundus photograph quality and how are they corrected?
Common image quality problems include: (1) Glare/reflection — caused by small undilated pupil or media opacity; fix by dilating the pupil or adjusting camera angle. (2) Blurry image — incorrect focus or patient movement; use the fixation target to steady the patient and re-adjust focusing knobs. (3) Dark or underexposed image — insufficient flash power or small pupil; increase flash intensity and dilate. (4) Overexposed (washed out) image — excessive flash; reduce flash power. (5) Ghost vessels — camera too close to eye; adjust working distance. (6) Eyelash artifact — lids not adequately retracted; use lid speculum or gently ask patient to open wider.
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