Haidinger's brushes in albinism: altered perception patterns in single cases.

PURPOSE: To characterize perception of Haidinger's brushes (HB) in individuals with albinism, in whom reduced macular pigment and abnormal foveal/Henle-fiber morphology may alter polarization sensitivity. METHODS: Three participants with oculocutaneous albinism (aged 19-29 years; two with nystagmus) viewed 468-nm polarized/unpolarized LED stimuli in a custom polarimetry device. Six randomized conditions varied polarization (0%, 20%, 50%, 100%) and polarizer rotation speed (2.3, 2.7, and 2.95 revolutions per second, rps); each tested eye completed three repetitions per condition. On each trial, participants reported percept presence/absence and qualitatively described any experienced percept. RESULTS: At 100% polarization, perception occurred at 2.7 and 2.95 rps in all tested eyes but was absent at 2.3 rps. At 50% polarization/2.7 rps, P1 and P2 reported blurred perception in both eyes, whereas P3 reported none. No responses occurred at 20% or 0% polarization. Reported patterns were consistently asymmetric, peripheral, flickering/wavy, and unlike the classical central bowtie. CONCLUSIONS: Individuals with albinism can perceive polarization-dependent entoptic phenomena, but the percept may be qualitatively altered. The findings suggest residual macular-pigment-related dichroism but do not isolate its retinal, corneal, or neural determinants. Quantitative studies with macular pigment optical density (MPOD) mapping, optical coherence tomography metrics of the Henle fiber layer (OCT-HFL), corneal polarimetry, and temporal-sensitivity testing are needed.