COT Ophthalmic Imaging and Photography 4 — Questions and Answers
Question 1: Enhanced depth imaging (EDI) OCT is specifically designed to improve visualization of which ocular structure?
- Corneal endothelium
- Vitreous cortex
- Choroid (Correct answer)
- Ganglion cell layer
Correct answer: Choroid
EDI-OCT inverts the sensitivity roll-off to place the zero-delay line deeper, improving signal from the choroid and sub-RPE layers.
Question 2: Which grading scale is most commonly used to standardize documentation of diabetic retinopathy severity from fundus photographs?
- Farnsworth-Munsell scale
- Early Treatment Diabetic Retinopathy Study (ETDRS) scale (Correct answer)
- Snellen visual acuity chart
- Humphrey field analyzer scale
Correct answer: Early Treatment Diabetic Retinopathy Study (ETDRS) scale
The ETDRS severity scale, developed from the landmark clinical trial, provides a standardized 13-level grading system for diabetic retinopathy.
Question 3: In fluorescein angiography, 'window defect' hyperfluorescence is caused by:
- Leakage from new vessels
- Loss of RPE blocking pigment revealing background choroidal fluorescence (Correct answer)
- Staining of fibrous tissue
- Pooling in a pigment epithelial detachment
Correct answer: Loss of RPE blocking pigment revealing background choroidal fluorescence
Window defects occur when RPE atrophy or thinning removes the normal blocking layer, allowing background choroidal fluorescence to shine through.
Question 4: A patient's OCT shows a 'double hump' or 'W-shape' reflectivity profile in the outer retina. This pattern is most associated with:
- Central serous chorioretinopathy
- Macular hole
- Vitelliform macular dystrophy
- Normal foveal pit anatomy (Correct answer)
Correct answer: Normal foveal pit anatomy
The normal foveal OCT profile shows a central pit flanked by the thicker parafoveal retina, creating a characteristic 'W' or double-hump appearance.
Question 5: Which photographic technique is used to map the anterior segment angle and document angle-closure risk?
- Specular microscopy
- Scheimpflug imaging (Pentacam) (Correct answer)
- Confocal scanning laser ophthalmoscopy
- Fluorescein angiography
Correct answer: Scheimpflug imaging (Pentacam)
Scheimpflug-based cameras (e.g., Pentacam) capture cross-sectional images of the anterior segment and can measure anterior chamber depth and angle parameters.
Question 6: When calibrating a fundus camera, the correct diopter compensation setting for a patient with −4.00 D myopia is:
- Add +4.00 D to the camera's diopter dial
- Set to −4.00 D on the camera's diopter dial (Correct answer)
- No adjustment needed — autofocus handles all corrections
- Add −2.00 D to account for the camera's internal optics
Correct answer: Set to −4.00 D on the camera's diopter dial
The camera's diopter compensation dial should be set to match the patient's approximate refractive error so the retina is in focus.
Question 7: OCT angiography (OCTA) generates images of retinal vasculature WITHOUT dye by detecting:
- Backscattered laser intensity differences
- Decorrelation signal from moving red blood cells between repeated B-scans (Correct answer)
- Doppler frequency shifts from arterial pulsation only
- Fluorescence emission from endogenous blood chromophores
Correct answer: Decorrelation signal from moving red blood cells between repeated B-scans
OCTA uses motion contrast algorithms that compare multiple repeated B-scans; moving erythrocytes produce a decorrelation signal that maps blood flow.
COT Ophthalmic Imaging and Photography 4
Enhanced depth imaging (EDI) OCT is specifically designed to improve visualization of which ocular structure?