Supplemental Testing 7 Flashcards

A patient with a dense nuclear cataract has a potential acuity meter (PAM) result of 20/40 in the affected eye. Postoperative visual acuity is measured at 20/80. Which explanation BEST accounts for this discrepancy?

Answer: Coexisting macular or optic nerve pathology was not detected by the PAM assessment

The PAM projects a grid through a small clear zone of the lens, bypassing the opacity to estimate potential retinal acuity. However, it cannot detect subtle macular disease or optic neuropathy that also limits vision. When postoperative acuity is worse than PAM predicted, coexisting retinal or optic nerve pathology is the most likely cause. PAM beam scatter through a dense cataract would actually worsen — not improve — the reading.

During Farnsworth-Munsell 100-Hue testing, a patient with a reported normal color vision history produces an error score heavily concentrated around caps 85–100 and caps 1–15. Which defect pattern does this MOST likely represent?

Answer: Tritan (blue-yellow) color deficiency

The FM 100-Hue test is arranged in a color circle. Errors concentrated at the blue-yellow axis (caps 85–100 wrapping around to caps 1–15) indicate a tritan defect — the blue-yellow axis of color confusion. Protan and deutan defects produce errors along the red-green axis, clustered around caps 45–55 and 20–30 respectively. Tritan defects are often acquired (e.g., from glaucoma, retinal disease, or drug toxicity) rather than congenital.

A technician performs photostress recovery testing and documents a recovery time of 55 seconds in the right eye and 18 seconds in the left eye. The patient's BCVA is 20/30 OU. This asymmetric result is MOST consistent with:

Answer: Macular disease in the right eye impairing photopigment regeneration

The photostress recovery test (PSRT) bleaches cone photopigment with a bright light and measures the time to recover baseline acuity. Recovery depends on the rate of photopigment regeneration in the RPE-photoreceptor complex. A prolonged PSRT (>50 seconds is abnormal; asymmetry >15 seconds is significant) localizes the deficit to the outer retina/macula — macular disease is the classic cause. Optic nerve lesions (optic neuritis, glaucoma) do NOT prolong PSRT because the RPE-photoreceptor machinery is intact. Amblyopia also does not prolong PSRT.

When performing electroretinography (ERG), a patient shows a markedly reduced b-wave amplitude with a relatively preserved a-wave under scotopic conditions. This 'electronegative ERG' pattern is MOST associated with:

Answer: X-linked retinoschisis or congenital stationary night blindness

The a-wave reflects photoreceptor (rod/cone) hyperpolarization, while the b-wave reflects ON-bipolar cell depolarization. An electronegative ERG — where b-wave amplitude is less than the a-wave — indicates dysfunction at the inner nuclear layer (bipolar cells) rather than the photoreceptors themselves. This pattern is the hallmark of X-linked retinoschisis (XLRS) and congenital stationary night blindness (CSNB), both of which affect ON-bipolar cell function. Retinitis pigmentosa reduces both waves proportionally (a-wave loss is primary). Cone dystrophy reduces photopic responses selectively.

A patient reports sudden-onset metamorphopsia. Amsler grid testing reveals a scotoma displaced INFERIORLY from fixation, though the patient complains that the distortion appears to be 'above' the central area. Which principle explains this spatial discrepancy?

Answer: Retinal image inversion means a superior retinal lesion projects as an inferior visual field defect perceived as 'above' fixation

Due to the optical inversion of the eye, an inferior retinal lesion corresponds to a superior visual field defect — the patient experiences distortion 'above' fixation — but on the Amsler grid (which maps the visual field, not the retina), the scotoma appears inferior. Conversely, a superior retinal lesion (e.g., superior macular hemorrhage) produces an inferior visual field scotoma perceived as distortion 'below.' The grid maps perceived visual space, so the scotoma location on the grid directly corresponds to where the patient sees the defect, not the retinal location. This distinction matters when correlating grid findings with fundus imaging.

During contrast sensitivity testing with a Pelli-Robson chart, a patient achieves a log contrast sensitivity of 1.50 in one eye. When tested with a Vistech VCTS chart, results suggest reduced sensitivity specifically at intermediate spatial frequencies (3–6 cpd) with relatively preserved high and low frequency sensitivity. This 'notch' pattern at intermediate frequencies is MOST characteristic of:

Answer: Multiple sclerosis-related optic neuritis

A selective loss of contrast sensitivity at intermediate spatial frequencies (3–6 cpd) with preservation at high and low frequencies creates a characteristic 'notch' pattern on the contrast sensitivity function (CSF). This is the hallmark of demyelinating optic neuritis, as seen in multiple sclerosis — demyelination selectively impairs the transmission of medium-frequency visual signals. Glaucoma tends to reduce sensitivity across all spatial frequencies, with greater loss at high frequencies as disease progresses. Uncorrected refractive error predominantly affects high spatial frequencies. Anisometropic amblyopia also affects high spatial frequencies selectively.