Visual Assessment 8 Flashcards

A patient with known amblyopia in the right eye presents for a COT exam. Distance BCVA is 20/80 OD. When a pinhole occluder is placed over the right eye, acuity improves to 20/40. What is the most accurate interpretation of this finding?

Answer: The amblyopia diagnosis should be reconsidered, as true amblyopia does not improve with pinhole

True amblyopia — by definition a cortical/neural suppression deficit — does not significantly improve with a pinhole occluder, because the pinhole only corrects optical blur, not neural processing deficits. Improvement to 20/40 with pinhole strongly suggests the 20/80 VA is driven by uncorrected or under-corrected refractive error rather than true amblyopia, and warrants re-evaluation of the refractive correction and the diagnosis.

During Humphrey SITA-Standard 24-2 perimetry, a patient's reliability indices show 0% false positives, 18% false negatives, and 22% fixation losses. Which of the following is the most clinically significant concern with this test?

Answer: Fixation losses above 20% suggest the patient may be looking away from the fixation target, reducing test reliability

Fixation losses above 20% are considered unreliable. They are measured by the Heijl-Krakau method (presenting a stimulus at the blind spot); if the patient responds, they were not fixating centrally. High fixation losses can produce artificially depressed or scattered results. While the false negative rate of 18% is borderline elevated (>33% is flagged), fixation losses >20% are the primary reliability flag here. High false negatives in an already damaged field can also be a sign of real scotomas, not just inattention.

A patient scores 11/14 on Ishihara color plates (using the 14-plate screening set). Which of the following is the most precise classification of this result?

Answer: Mild red-green deficiency — a score below 13/14 on the screening set indicates deficiency

On the standard 14-plate Ishihara screening set, a score of 13 or 14 correct is considered normal. Scoring 12 or below indicates a red-green color deficiency (protan or deutan). At 11/14, this patient clearly falls into the deficient range. Ishihara plates are specifically designed to detect red-green deficiencies and cannot reliably detect blue-yellow (tritan) defects — ruling out answer C. Answer D is incorrect because Ishihara does provide a pass/fail classification even if it doesn't quantify severity as precisely as FM-100.

When testing near visual acuity with a Jaeger chart, a patient reads J1 easily at 14 inches but struggles with J1 at 16 inches and cannot read it at 18 inches. Assuming no accommodative disorder, what is the most likely explanation?

Answer: Jaeger notation is not standardized in size across manufacturers, making distance-specific interpretation unreliable

Jaeger notation lacks a universal standardized letter size — J1 on one manufacturer's chart may differ from J1 on another's. Furthermore, Jaeger testing is typically performed at a specified distance (commonly 14 or 16 inches), and performance variation across distances in a patient without accommodative dysfunction is more likely a function of chart variability and magnification effects than pathology. This is a well-known limitation of Jaeger notation compared to standardized M-notation or Snellen-equivalent near charts.

A patient with a dense posterior subcapsular cataract (PSC) undergoes contrast sensitivity testing under photopic conditions and shows markedly reduced contrast sensitivity at mid and high spatial frequencies. Under mesopic (dim light) conditions, her contrast sensitivity worsens dramatically more than would be expected compared to normal aging. What physiological mechanism best explains this disproportionate mesopic decline?

Answer: Pupil dilation under dim light increases the effective aperture, allowing more light to scatter through the peripheral PSC opacity

Under mesopic (dim) conditions, the pupil dilates to allow more light in. A PSC is located at the central posterior capsule, directly in the optical axis. As the pupil enlarges, the effective optical zone expands and more incident light passes through or near the opacity, dramatically increasing forward light scatter. This scatter degrades contrast and causes glare. This is why PSC cataracts are classically associated with symptoms worse in dim light and with oncoming headlights, and why mesopic contrast sensitivity is disproportionately affected.

Using the Titmus stereofly test, a patient correctly identifies the fly as three-dimensional but fails all nine animal targets and all circles. A second patient fails to perceive the fly in 3D but correctly identifies 3 of the 9 animals. Which conclusion is best supported?

Answer: Patient 2 has better stereoacuity than Patient 1 because the animal targets require finer disparity detection than the fly

The Titmus stereofly is a gross stereopsis target detectable at approximately 3000 arcseconds of disparity — it is the coarsest target on the test and can be perceived through monocular cues (the wings create a vivid 3D percept even monocularly in some patients). The nine animal targets require ~400–100 arcseconds, and the Wirt circles range from 800 to 40 arcseconds. Patient 1's isolated fly response with failure of all finer targets strongly suggests a monocular cue response rather than true stereopsis. Patient 2, who detects some animal targets, demonstrates finer true binocular disparity detection despite failing the fly.