Mixed Deck — All COT Topics Flashcards

A patient with known multiple sclerosis undergoes visual field testing. The result shows a unilateral, dense central scotoma in the right eye with a normal left eye field. The right eye visual acuity is 20/200. Which finding on visual field testing would MOST help distinguish optic neuritis from a macular lesion as the cause?

Answer: A cecocentral scotoma pattern extending from the blind spot to fixation

A cecocentral scotoma — a defect connecting the blind spot to the central fixation area — is characteristic of optic nerve disease affecting the papillomacular bundle, as seen in optic neuritis, toxic/nutritional optic neuropathies, and Leber's hereditary optic neuropathy. Macular disease typically causes a pure central scotoma without the connection to the blind spot. While an RAPD supports optic nerve disease, it doesn't differentiate the scotoma pattern. A preserved temporal crescent indicates intact far peripheral nasal retina and would not differentiate these conditions. A vertical step at the midline is characteristic of chiasmal or post-chiasmal lesions.

Which slit-lamp illumination technique is best for detecting corneal edema and stromal haze?

Answer: Sclerotic scatter

Sclerotic scatter illuminates the cornea via total internal reflection from the limbus, making stromal haze and edema visible as a glow against a dark background.

Which topical ophthalmic antibiotic is a fluoroquinolone commonly used to treat bacterial conjunctivitis and corneal ulcers?

Answer: Ciprofloxacin

Ciprofloxacin is a broad-spectrum fluoroquinolone antibiotic that inhibits bacterial DNA gyrase and is effective against both gram-positive and gram-negative organisms causing ocular infections.

The foveal avascular zone (FAZ) receives its oxygen supply primarily through which mechanism?

Answer: Diffusion from the underlying choriocapillaris

The FAZ is devoid of retinal capillaries by definition. The foveal photoreceptors — the most metabolically demanding cells in the retina — rely entirely on diffusion of oxygen and nutrients from the choriocapillaris across Bruch's membrane and the retinal pigment epithelium. This is why macular degeneration, which disrupts the choriocapillaris, is so devastating to central vision.

What is the focal length of a +4.00 D lens?

Answer: 0.25 meters

Focal length (f) = 1 / power in diopters = 1 / 4.00 = 0.25 meters.

On a properly aligned A-scan, the retinal spike should be:

Answer: Sharp and perpendicular (90°) with high amplitude

A perpendicular, high-amplitude retinal spike indicates the probe is aligned along the visual axis and measurement is accurate.

If a spectacle Rx is −10.00 D at a vertex distance of 12 mm, what is the approximate contact lens power needed?

Answer: −9.00 D

For high minus lenses, moving the lens to the cornea reduces effective power; the CL power is approximately −9.00 D at the corneal plane.

A patient scheduled for cataract surgery tells the ophthalmic technician they are unsure whether they want to proceed and have not signed the consent form. The surgeon is ready to begin. What is the most appropriate action for the technician?

Answer: Notify the surgeon that the patient has not consented and is uncertain

Informed consent must be obtained voluntarily before any procedure. The technician's duty is to halt preparation and notify the surgeon so the patient can have their questions addressed and consent obtained properly. Proceeding without consent violates patient rights and exposes the facility to legal liability.

The typical ultrasound frequency used in ophthalmic A-scan biometry is:

Answer: 10 MHz

Ophthalmic A-scans use 10 MHz ultrasound to achieve adequate resolution for ocular structures.

On a Humphrey SITA-Standard 30-2 printout, a patient shows a dense inferior arcuate scotoma. The probability plot shows that the defect respects the horizontal meridian precisely. The technician notes a superior disc pallor on slit-lamp biomicroscopy. Based on the neuro-ophthalmic localization principle, which statement BEST describes the anatomical basis for a field defect that respects the horizontal meridian?

Answer: The raphe of the retinal nerve fiber layer creates a horizontal boundary of axonal trajectories at the fovea, preserved as a meridional border through the visual pathway

The horizontal meridian respecting defect (horizontal step) in glaucoma and other optic nerve diseases arises from the anatomy of the retinal nerve fiber layer: superior and inferior temporal nerve fibers are separated at the horizontal raphe (temporal to the fovea) and travel in completely separate superior and inferior arcuate bundles to the optic disc. Damage to either bundle produces an arcuate or altitudinal defect that sharply respects the horizontal meridian. This separation is preserved through the optic nerve but is NOT maintained posterior to the LGN—cortical lesions produce quadrantic or hemianopic defects respecting the vertical, not the horizontal, meridian.

When performing a visual assessment of a patient's respiratory effort, which finding would MOST indicate increased work of breathing?

Answer: Use of sternocleidomastoid muscles during inhalation

Use of accessory muscles such as the sternocleidomastoid during inhalation is a classic visual sign of increased work of breathing. Normal breathing relies primarily on the diaphragm and intercostals. Symmetric chest rise, a normal respiratory rate of 14 breaths/min, and pink mucous membranes are all reassuring normal findings.

A patient claims vision of 20/400 in the right eye following a workplace injury. Without informing the patient, the examiner positions the Snellen chart at 10 feet instead of the standard 20 feet. The patient reads the line labeled '20/100' with effort. What is this patient's calculated actual visual acuity for this eye?

Answer: 20/50

When the standard chart is viewed at half the normal distance (10 feet instead of 20 feet), every optotype subtends twice its standard angular size at the eye. To calculate actual acuity: (testing distance ÷ standard distance) × denominator of line read = (10 ÷ 20) × 100 = 50. The patient's actual acuity is therefore 20/50 — far better than the claimed 20/400. This half-distance Snellen technique is a validated method for detecting functional (non-organic) vision loss when the patient's claimed acuity is inconsistent with their behavior or other objective findings.

When performing lensometry on a high-minus lens (−14.00 D) using a standard manual lensometer, the technician notices the mires cannot be focused even at the extreme end of the power wheel. The MOST appropriate corrective action is:

Answer: Use a +10.00 D auxiliary lens held against the back surface of the lens being tested to shift the power into measurable range

Most standard lensometers have a measurement range of approximately −20.00 D to +20.00 D, but mire clarity at extremes can degrade. For very high-power lenses beyond comfortable lensometer range, a known auxiliary lens (e.g., +10.00 D) is placed against the back surface. The lensometer reading is then algebraically combined with the auxiliary lens power using the vergence formula to determine the true lens power. Flipping the lens introduces back-vertex vs. front-vertex measurement errors, which are clinically significant at high powers.

When calibrating a Goldmann tonometer, the check weight is applied and the drum is set to 2 g. What result indicates the instrument is correctly calibrated?

Answer: The balance arm swings freely to the up-stop

Correct calibration at the 2 g check weight causes the balance arm to swing to the up-stop, confirming the spring tension is accurate.

A technician must measure the IOP of a patient who has a heavily scarred and irregular cornea from a previous injury. Which instrument would provide the most reliable reading in this scenario?

Answer: Tono-Pen or iCare tonometer

The Tono-Pen and iCare rebound tonometer are less affected by corneal irregularity and scarring than applanation or air-puff tonometers. They take multiple small-area readings, which are then averaged, providing a more reliable IOP measurement on compromised corneas.

A technician is performing retinoscopy on a new patient and finds the reflex to be very dim and slow-moving. Which of the following is the most likely cause for these findings?

Answer: A high refractive error

A high refractive error causes the light rays to be far from neutralized, resulting in a retinoscopic reflex that is dim, wide, and slow-moving. As lenses are added and neutrality is approached, the reflex becomes brighter, narrower, and faster. Accommodation would cause the reflex to fluctuate, not necessarily be dim and slow.

A patient presents with an inability to abduct their left eye (turn it outward). A lesion of which cranial nerve is the most likely cause of this deficit?

Answer: Cranial Nerve VI (Abducens)

Cranial nerve VI, the abducens nerve, innervates the lateral rectus muscle, which is solely responsible for abduction (outward movement) of the eye. Therefore, a lesion of CN VI would result in an inability to abduct the eye on the affected side. CN III innervates most of the other extraocular muscles, and CN IV innervates the superior oblique.

Bruch's membrane separates the retinal pigment epithelium from which structure?

Answer: Choriocapillaris

Bruch's membrane is a pentalaminar structure between the RPE and the choriocapillaris, important in macular disease pathogenesis.

A 38-year-old patient with a history of resolved optic neuritis in the right eye reports a peculiar symptom: when watching a pendulum swing side-to-side, it appears to travel in an elliptical arc rather than a straight line, and depth perception is disturbed. Supplemental testing with which modality would most directly quantify the physiological basis of this symptom?

Answer: Visual evoked potential (VEP) comparing P100 latency between the two eyes

This patient is describing the Pulfrich phenomenon, which occurs when there is an inter-ocular difference in neural transmission speed — most commonly from demyelinating optic neuritis causing a prolonged latency in one eye. The brain interprets the temporal offset as a spatial depth disparity, causing moving objects to appear to travel in an elliptical arc. VEP testing directly measures P100 latency in each eye; a prolonged latency in the previously affected eye confirms the inter-ocular latency asymmetry that generates this phenomenon.

When performing A-scan on a silicone oil-filled eye, the technician must:

Answer: Use a silicone-specific velocity setting (~980 m/s)

Silicone oil has a much lower sound velocity (~980 m/s) than vitreous, requiring adjustment to avoid axial length errors.