Ophthalmic Imaging and Photography Flashcards

During fluorescein angiography, a lesion that is hyperfluorescent in the early arteriovenous phase and becomes progressively LESS fluorescent in the late phase is best described as demonstrating which pattern?

Answer: Early hyperfluorescence with late washout (pooling reversal)

True late-phase washout (sometimes called 'pooling reversal') occurs when dye does not accumulate in the tissue or subretinal space but instead diffuses away, causing the lesion to appear less bright over time. This contrasts with staining (which brightens or persists late) and pooling (which increases). Recognizing this pattern helps differentiate certain serous detachments and vessel anomalies from active leakage.

On fundus autofluorescence (FAF) imaging, a ring of INCREASED autofluorescence surrounding a central area of decreased autofluorescence in a patient with geographic atrophy is clinically significant because the ring represents:

Answer: Metabolically stressed RPE cells at the leading edge of atrophy containing excess lipofuscin

In geographic atrophy, the hyperautofluorescent ring surrounding the atrophic zone represents RPE cells that are under oxidative stress and accumulating abnormal amounts of lipofuscin — the primary source of autofluorescence. These cells are at high risk of dying and joining the atrophic area. This ring pattern is predictive of atrophy progression rate and is an important biomarker in clinical trials.

When calibrating a fundus camera for standardized disc photography in a patient with high myopia (–10.00 D), the photographer must apply a correction factor to accurate linear measurements because:

Answer: High minus lenses in the indirect condensing system shift the nodal point, invalidating the Littmann correction formula assumptions

The Littmann formula for correcting fundus camera magnification assumes a standard nodal point position. In high myopia, the elongated globe shifts the position of the eye's second nodal point posteriorly, and when strong minus auxiliary lenses are introduced into the optical path, the effective magnification changes in a way that the standard formula does not fully account for. The correction factor must incorporate the patient's refractive error (the 'ametropia correction') to yield accurate disc measurements.

In optical coherence tomography angiography (OCTA), the 'projection artifact' that causes superficial vascular flow signal to appear incorrectly superimposed on the deep capillary plexus or outer retinal slabs is caused by:

Answer: Fluctuations in backscattering from moving red blood cells in superficial vessels modulating the OCT signal in layers directly beneath them

Projection artifacts in OCTA occur because moving red blood cells in superficial vessels cause intensity fluctuations in the OCT signal that propagate through underlying tissue layers. The decorrelation signal used to detect flow is also present in deeper layers directly below the vessel, creating 'ghost' vessels in slabs such as the deep capillary plexus or outer avascular retina. Modern OCTA devices apply projection-removal algorithms to mitigate this, but residual artifact remains a known interpretive pitfall.

A photographer is imaging a patient who has undergone prior vitrectomy with silicone oil tamponade still in place. Compared to a phakic eye with a normal vitreous, which of the following adjustments is MOST critical when performing B-scan ultrasonography in this patient?

Answer: Inverting the image orientation because sound velocity in silicone oil reverses the apparent depth of lesions

Silicone oil has a significantly different acoustic velocity (~980 m/s) compared to vitreous or aqueous (~1,532 m/s). B-scan ultrasonography calculates depth based on the assumed sound velocity of the ocular media. In a silicone-oil-filled eye, the lower speed causes the ultrasound to take longer to traverse the oil, making structures behind the oil appear deeper (more posterior) than they actually are. Technicians must be aware that image depth calibration is inaccurate and apply a correction factor, or the apparent position of retinal detachments, membranes, and foreign bodies will be misleading.

During indocyanine green angiography (ICGA), the 'wash-in/wash-out' kinetics of ICG differ fundamentally from fluorescein because ICG is approximately 98% protein-bound in plasma. Which of the following late-phase ICGA findings is a DIRECT consequence of this protein-binding property?

Answer: ICG produces persistent late choroidal staining because the dye-protein complex is too large to exit normal choroidal fenestrations, making hypofluorescent areas in the late phase reliably indicate choroidal pathology

Because ICG binds tightly to plasma proteins (primarily albumin), the large dye-protein complex cannot exit through normal choroidal vessel fenestrations. This means the choroid normally retains ICG signal in mid-to-late phase. Areas of late-phase hypofluorescence (dark spots) therefore represent tissue where the ICG-protein complex is absent or has been washed out — this reliably indicates choroidal pathology such as choroidal ischemia, infiltration, or areas of non-perfusion. This property is the basis for using ICGA to diagnose conditions like polypoidal choroidal vasculopathy and multifocal choroiditis.