Optometry & Visual Performance 192 Volume 14 | Issue 2 | June 2026 or spot (or sees it distorted/absent) despite good instruction and proper technique, this is a strong red flag for organic macular disease rather than (or in addition to) eccentric fixation. • Haidinger Brush is an entoptic phenomenon created by the radially arranged, dichroic (polarization-sensitive) macular pigment (xanthophylls) in the fovea. When the patient views a field of polarized blue light (through a rotating polarizer or specialized filter), the pigment differentially absorbs light depending on its polarization orientation, producing a visible propeller- or hourglass-shaped brush that appears to the patient to rotate with the polarizer. This brush is perceived only when the light stimulates the central fovea; therefore, with eccentric fixation, the brush appears displaced from the fixation target in the direction opposite the eccentric point. • The Maxwell’s Spot arises from the higher concentration of macular pigment (lutein and zeaxanthin) in the central fovea, which strongly absorbs short-wavelength (blue) light. When viewing a uniform blue field (e.g., through a blue filter or Maxwell’s spot tester), the foveal region appears as a dark central spot or shadow due to this selective absorption. Because the spot marks the true anatomical fovea, any misalignment between the spot and the patient’s reported fixation point directly confirms EF. Neutral Density Filter Test The neutral density (ND) filter test is a simple prognostic and diagnostic tool that helps confirm the functional (cortical) nature of amblyopia and differentiate it from organic causes of reduced vision. It exploits the fact that the amblyopic visual system is relatively resistant to overall luminance reduction because of cortical suppression and altered contrast processing. A ND filter decreases overall luminance without inducing a color change and produces a corresponding decrease in central visual acuity in healthy eyes. To perform the test, first measure BCVA of amblyopic eye monocularly with the optimal monocular refractive correction --> place a standardized ND filter over the corrected amblyopic eye (commonly 1.0 or 2.0 log units) --> remeasure acuity of amblyopic eye through filter. In functional amblyopia, the amblyopic eye shows minimal or no drop in visual acuity (often <1 line), because the cortical suppression and altered contrast/ luminance processing in V1 make the amblyopic system relatively insensitive to overall brightness reduction. In contrast, an organic lesion (e.g., optic neuropathy, macular dystrophy, or media opacity) typically causes a marked drop (2 or more lines) in acuity with the filter. This relative luminance sparing in the amblyopic eye strongly supports a functional diagnosis. The ND filters can also be used to quantify the depth of suppression. The patient views the Worth 4-dot target through red-green filters to identify the current suppression pattern --> place ND filters of increasing log units over the fellow (non-amblyopic) eye to reduce its luminance until the interocular signal is balanced in the brain --> the specific density value at which the patient breaks suppression or achieves fusion—reporting all five dots if diplopic or four dots if fused—serves as the neutralization point, providing a precise metric for the strength of the cortical suppression. Performing Sanet-Vergara-Press Best Binocular Prescription (BBP) The Best Binocular Prescription (BBP) is a neurofunctional approach that prioritizes the lens powers that give the best overall binocular performance rather than the strongest monocular acuity in each eye. It is especially useful for hyperopic anisometropic amblyopia. The goal is to minimize binocular competition (suppression) and maximize binocular summation, fusion, and stereopsis to decrease the amount of cortical suppression (the cause of amblyopia and visual acuity loss) leading to improvement in visual acuity (the symptom of amblyopia). Step 1: Obtain Accurate Baseline Refraction: Perform dry retinoscopy and subjective refraction (if possible) --> Perform full cycloplegic refraction (using cyclopentolate or 2 drops of tropicamide) --> Record the maximum plus accepted monocularly for each eye. Step 2: Polarized Binocular Testing: Turn on the polarized acuity chart and use polarized glasses over the trial frame --> Place the cycloplegic (or dry) findings into the trial frame. Start with the full monocular prescription in both eyes. Instruct the patient to look at the letters with both eyes open and report when they are clearest and most comfortable --> Begin reducing the plus power (usually in the more hyperopic/ amblyopic eye) in 0.25 D steps. After each adjustment, ask: Is the chart clearer, the same, or blurrier? Is it more comfortable? Continue reducing plus until you reach the point where binocular visual acuity is maximized and the patient reports best overall clarity/comfort. --> Fine-tune both eyes as needed (sometimes you
RkJQdWJsaXNoZXIy MjEyMDQ0Nw==