Visual Field Testing Flashcards

A patient with suspected normal-tension glaucoma undergoes Humphrey Visual Field testing. The Mean Deviation (MD) is -4.2 dB and the Pattern Standard Deviation (PSD) is 6.8 dB. The Glaucoma Hemifield Test (GHT) reports 'Outside Normal Limits.' Which additional index would BEST help distinguish true localized nerve fiber layer loss from diffuse media opacity in this case?

Answer: Corrected Pattern Standard Deviation (CPSD)

CPSD (Corrected Pattern Standard Deviation) mathematically removes the component of variability attributable to diffuse loss or media opacity, leaving only the localized, pattern-based deviation. A high CPSD despite media haze points to true focal nerve fiber loss rather than a global reduction from cataract or corneal irregularity. VFI is useful for progression tracking but doesn't separate diffuse from focal loss. SF reflects within-test variability. Foveal Threshold is a sensitivity measure at fixation.

During a 24-2 SITA-Standard Humphrey field test, a technician notices the fixation loss rate is 28%, the false-positive rate is 4%, and the false-negative rate is 31%. Which combination of reliability indices most critically invalidates the interpretation of a superior arcuate defect seen on this field?

Answer: High fixation loss combined with high false-negative rate

A high false-negative rate (>33% is flagged, but >20–25% is clinically suspicious) combined with high fixation losses together strongly suggest patient fatigue, inattention, or advanced disease causing unreliable responses—making any defect pattern uninterpretable. High false-positives ('trigger-happy' patients) cause artificially good results and would mask defects, not create them. Fixation losses alone at 28% are borderline, but paired with high false-negatives, the field cannot be trusted.

A patient returns for repeat Goldmann kinetic perimetry after prior automated testing was unreliable due to severe cognitive impairment. The examiner uses the I4e isopter to map the peripheral field and then uses the I2e isopter centrally. The I2e isopter is unexpectedly larger than the I4e isopter in the superior quadrant. What is the MOST likely explanation?

Answer: A ring scotoma between the I2e and I4e isopters

In Goldmann perimetry, larger/brighter stimuli (I4e) should always produce isopters that are equal to or larger than those of smaller/dimmer stimuli (I2e). If the I2e isopter extends beyond the I4e boundary in any quadrant, it indicates an annular (ring) scotoma—an area of depressed sensitivity located between the two isopter boundaries, where the dimmer target was perceived but the brighter one was not. This pattern can be seen in conditions like retinitis pigmentosa. Examiner speed artifact would affect all quadrants uniformly.

When performing frequency doubling technology (FDT) perimetry as a glaucoma screening tool, which underlying neural mechanism does this test exploit?

Answer: The non-linear response of My (parasol) ganglion cells to low spatial-frequency, high temporal-frequency gratings

FDT exploits a specific property of a subset of large-diameter (My) retinal ganglion cells—a subtype of the magnocellular (M-cell) pathway—that respond non-linearly to low spatial-frequency sinusoidal gratings flickering at high temporal frequency (≥15 Hz). This non-linearity causes the perceived spatial frequency to appear doubled. These My cells are hypothesized to be selectively vulnerable early in glaucoma, making FDT sensitive for early detection. The parvocellular pathway is not the primary mechanism, and S-cone/koniocellular pathways underlie short-wavelength automated perimetry (SWAP), not FDT.

A 52-year-old patient on hydroxychloroquine therapy for 7 years undergoes 10-2 Humphrey visual field testing. The report shows a paracentral scotoma at 4° and 8° eccentricity in both eyes, with a 'bull's-eye' pattern on fundus autofluorescence. The technician is asked to repeat the test to confirm. Which testing modification would provide the HIGHEST sensitivity for confirming early hydroxychloroquine toxicity?

Answer: Using the 10-2 pattern with a blue stimulus on a yellow background (SWAP protocol)

Short-wavelength automated perimetry (SWAP), which uses a blue stimulus on a yellow background, isolates the S-cone (short-wavelength) pathway. S-cones are concentrated in the parafoveal region and are preferentially damaged early in hydroxychloroquine toxicity, often before conventional white-on-white perimetry detects a deficit. The 10-2 pattern is correct for this condition since toxicity appears within the central 10°, but adding the SWAP protocol increases sensitivity for the earliest cone-selective changes. Increasing background luminance (option C) is not a standard protocol for toxicity screening.

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.