Ophthalmic Imaging and Photography Flashcards

During fluorescein angiography, a patient develops a 'blocking defect' that appears hypofluorescent in both early and late phases. Which of the following is the MOST likely cause?

Answer: Subretinal hemorrhage from a choroidal neovascular membrane

A blocking defect that is hypofluorescent in both early AND late phases indicates an opaque substance physically blocking the choroidal fluorescence from reaching the camera — subretinal hemorrhage is the classic example. Geographic atrophy and RPE atrophy over drusen produce window (transmission) defects that are hyperfluorescent. A PED typically shows early hyperfluorescence with late staining or pooling, not consistent blocking.

When performing optical coherence tomography angiography (OCTA), the image is degraded by a projection artifact showing retinal vasculature superimposed on the choriocapillaris slab. What is the technical basis of this artifact?

Answer: Pulsatile flow-induced decorrelation signal from superficial vessels casting shadows onto deeper slabs

Projection artifacts in OCTA arise because moving blood in superficial retinal vessels modulates the backscattered signal from deeper tissue. The decorrelation signal 'projects' downward through all deeper slabs, making superficial vessel patterns appear falsely in the outer retina and choriocapillaris slabs. This is distinct from motion artifacts (caused by bulk eye movement) or specular reflections. Projection removal algorithms attempt to correct for this.

A 45-year-old patient with high myopia undergoes wide-field fundus photography. The temporal periphery appears disproportionately darker than the posterior pole despite optimal exposure settings. Which parameter adjustment would BEST correct this without re-photographing?

Answer: Apply peripheral illumination compensation (edge brightening) in the imaging software post-capture

Wide-field systems inherently produce peripheral dimming due to the cosine-fourth law of illumination fall-off and the oblique angle of peripheral capture. Post-capture peripheral illumination compensation (also called field curvature correction or edge brightening) is the standard software correction that applies a gradient filter to equalize brightness across the image. Increasing flash intensity uniformly would overexpose the posterior pole. Aperture reduction affects depth of field, not peripheral brightness uniformity. Channel separation changes contrast, not illumination distribution.

During indocyanine green (ICG) angiography of a patient with suspected polypoidal choroidal vasculopathy (PCV), you notice a cluster of hyperfluorescent nodules along the inner border of the choroidal neovascular network in the early phase. The CORRECT interpretation of this finding is:

Answer: Polypoidal lesions representing aneurysmal dilations of the choroidal vasculature

The pathognomonic ICG finding in PCV is the appearance of hyperfluorescent polypoidal lesions visible in the early-to-mid phase as clustered nodules ('bunch of grapes' pattern) at the margin of a branching choroidal vascular network. These represent true aneurysmal or polypoid dilations of the inner choroidal vasculature. ICG is essential for PCV diagnosis because these polyps are often missed on fluorescein angiography and OCT alone. Window defects are an FA term, and late staining describes a different FA phenomenon.

A technician captures a confocal scanning laser ophthalmoscope (cSLO) fundus autofluorescence (FAF) image. The fovea appears as a dark zone surrounded by a normal-intensity background, but a second ring of slightly increased autofluorescence is noted just outside the foveal dark zone. In the absence of disease, what is the MOST likely explanation for this pericentral hyperautofluorescent ring?

Answer: The transition zone where macular pigment density rapidly decreases, resulting in less quenching of RPE lipofuscin fluorescence

In normal FAF, the fovea is dark due to the absorptive properties of macular pigment (lutein and zeaxanthin), which quench lipofuscin autofluorescence. Just outside the foveal center, macular pigment concentration drops sharply, reducing quenching — this creates a subtle ring of relatively higher FAF signal around the foveal dark zone. This is a normal physiological finding. The same principle is used in macular pigment optical density (MPOD) measurements. This should not be confused with the pathological pericentral ring seen in conditions like Stargardt disease.

When calibrating a Goldmann-compatible fundus camera for stereoscopic disc photography using the simultaneous stereoscopic method, the technician notices that the two half-images have unequal magnification on review. Which of the following is the MOST likely cause?

Answer: The beam splitter prism is laterally decentered relative to the camera's optical axis

In simultaneous stereoscopic fundus photography, the beam splitter divides the exit pupil into two half-apertures that image the fundus from slightly different angles onto two separate film planes or sensor areas. If the prism is laterally decentered from the optical axis, one light path subtends a larger effective aperture angle than the other, producing different magnification (and potentially different distortion) in each half-image. A small pupil causes symmetric vignetting of both paths equally. Diopter compensation affects focus but not relative magnification between the two channels. Flash sync issues would cause blur in one image, not magnification difference.