Quantitative polarized light microscopy of unstained mammalian cochlear sections

Abstract

Abstract. Hearing loss is the most common sensory deficit in the world, and most frequently it originates in the inner ear. Yet, the inner ear has been difficult to access for diagnosis because of its small size, delicate nature, complex three-dimensional anatomy, and encasement in the densest bone in the body. Evolving optical methods are promising to afford cellular diagnosis of pathologic changes in the inner ear. To appropriately interpret results from these emerging technologies, it is important to characterize optical properties of cochlear tissues. Here, we focus on that characterization using quantitative polarized light microscopy (qPLM) applied to unstained cochlear sections of the mouse, a common animal model of human hearing loss. We find that the most birefringent cochlear materials are collagen fibrils and myelin. Retardance of the otic capsule, the spiral ligament, and the basilar membrane are substantially higher than that of other cochlear structures. Retardance of the spiral ligament and the basilar membrane decrease from the cochlear base to the apex, compared with the more uniform retardance of other structures. The intricate structural details revealed by qPLM of unstained cochlear sections ex vivo strongly motivate future application of polarization-sensitive optical coherence tomography to human cochlea in vivo.

Polarization microscopy for characterizing fiber orientation of ocular tissues

“…Multiple images were acquired with various filter orientations relative to the sample separated by 45°. The images were registered and the signal intensities from the multiple images were used to compute local orientation at each pixel [23]. For visualization, the fiber orientation at each pixel was also weighted by a parameter we denoted "energy" (Eq.…”

“…Tissue samples were imaged using standard bright-field imaging as well as PLM according to the protocols described by Kalwani and colleagues [23]. Briefly, a white light source and two polarizing filters were used (Hoya, Tokyo, Japan).…”

“…PLM has been proven effective to characterize collagen of tendons [20,21], ligaments [22] and other soft tissues [23]. The possibility of using PLM in the cornea was discussed almost two decades ago for ex-vivo tissues [24], and more recently to study the cornea stroma in vivo [25].…”

Quantitative polarized light microscopy of human cochlear sections

“…We have recently demonstrated that quantitative polarized light microscopy (qPLM) detects differences in polarization dependent optical properties of key intracochlear structures, as evaluated using unstained mouse cochlear sections [4], while being faster and cheaper than immunohistochemistry. The current study explores the utility of qPLM in imaging human cochlear sections.…”

“…Today, the only source of information about the cellular basis of human deafness is cadaveric human temporal bones that house the inner ear. To enable future cellular-level intracochlear imaging in alive humans, we have been exploring optical imaging tools [3,4] because optics provides higher spatial resolution at a lower cost than techniques based on ionizing radiation or magnetic resonance.…”