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 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.

Fundus Photography: Technique and Clinical Applications

Q: 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.

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.

Fundus Camera Types and Field of View

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.

Patient Preparation and Positioning

Pre-Photography Checklist

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?

Patient Positioning

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. — Try not to blink — I\'ll take the picture quickly.

Focusing Technique and Standard Image Set

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.

Bright vs. Dark Field Illumination

Red-Free (Green) Filter

Eliminates red wavelengths, enhancing contrast of blood vessels, nerve fiber layer, and hemorrhages (which appear dark). Excellent for:

Nerve fiber layer assessment (peripapillary RNFL defects)
Vascular detail (arterioles vs. venules)
Detecting subtle retinal hemorrhages
Epiretinal membrane visibility

Standard Color (White Flash)

Full-color photograph showing the fundus as seen clinically. Best for:

Overall fundus documentation
Drusen characterization (hard vs. soft)
Pigmentary abnormalities
Disc color assessment (pink, pale, hyperemic)
Standard medical record documentation

Standard Posterior Pole Image Set

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 Disc Photography

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)

Take first disc-centered image from standard position
Shift joystick approximately 3mm to one side
Re-center the disc and take second image
The two images form a stereo pair when viewed with stereo viewer

Quality Requirements

Both images must be focused equally
Flash intensity must be identical for both
Disc position should mirror each other in the two images
Patient must maintain fixation between images

OCT: Overview for Ophthalmic Assistants

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: COA Role and Basics

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 Quality Troubleshooting

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

Documentation and Longitudinal Comparison

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

Always label images: OD or OS, date, view type (disc/macula-centered, field number)
Use consistent camera settings and field of view across visits for valid comparison
Store images in the patient's EHR with correct encounter link
Note pupil size, dilation status, and media clarity in documentation
Flag image quality issues for physician review rather than submitting poor-quality images

Serial Comparison: What Physicians Look For

→Glaucoma: Progressive increase in cup-to-disc ratio, disc hemorrhage appearance, RNFL defect enlargement
→AMD: New soft drusen, geographic atrophy expansion, choroidal neovascular membrane development
→Diabetic retinopathy: New hemorrhages, exudate progression, neovascularization development
→Treatment response: Reduction in exudate, hemorrhage resolution, lesion regression after laser or injection

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