2023-08-29 04:00:03
Obtaining precise information on the structure of the cornea is essential to understanding its ability to guarantee good visual acuity. A team has developed an original approach combining so-called SHG microscopy and polarimetry to image the microstructure in the form of lamellae of ten human corneas.
Image d’illustration Pixabay
One of the fundamental roles of the cornea is to contribute to the focusing of light (Light is all the electromagnetic waves visible by the eye…) on our retina (The retina is the sensitive organ of the vision. Of diencephalic origin, it is a…). Its curved shape, and therefore its focusing capacity, must be perfectly stable in order to ensure a sharp image despite the various shocks and friction received during the day.
The cornea is thus composed of several hundred lamellae of collagen stacked on top of each other according to variable orientations. But the transparency (A material or an object is qualified as transparent when it allows itself to be crossed by…) of this tissue, essential for visual acuity, is a brake on its imagery (Imagery consists first in the manufacture and trade of physical images which…) by conventional optical microscopes. In fact, the insufficient characterization of the lamellar structure of the cornea currently limits the understanding of the link between structure and function of this tissue, particularly in terms of its mechanical properties. Thus, certain pathologies linked to a defective structure of the cornea, for example keratoconus (Keratoconus (from the Greek kerato, horn, cornea and konos, cone) is a disease…), are still poorly understood today.
In a recent work, a team from the Laboratory of Optics and Biosciences (LOBCNRS / Ecole Polytechnique / Inserm) used a recent three-dimensional (3D) optical imaging technique, microscopy (Microscopy is the observation of a sample (placed in a microscopic preparation…) by generation of a second ( Second is the feminine of the adjective second, which comes immediately following the first or which…) harmonic (In several fields, a harmonic is a constituent element of a periodic phenomenon…) (known as “SHG” microscopy) to visualize the collagen specifically without any prior marking.The originality of their approach is to play on the polarization (the polarization of electromagnetic waves; the polarization due to moments…) of light (the direction of the electric field (In physics , an electric field is a field created by particles…) of the optical wave) to reveal the direction of the collagen fibrils that make up the lamellae of the cornea. This imaging is carried out in reflection, which allows the should be considered as a diagnosis (Diagnosis (from the Greek δι?γνωση, diágnosi, from…) in vivo, and also gives much more precise results than in transmission.
Ten intact human corneas might thus be characterized, and were used to validate the method, since SHG polarimetry had never been implemented on tissues of such thickness (approximately 600 µm). In particular, the researchers show for the first time that although the lamellae of the human cornea are globally oriented in two perpendicular directions, their majority direction changes with depth.
This study opens the way to promising new characterizations of the cornea, such as the mapping of the size and distribution of the lamellae according to the depth, but also according to the position (center or periphery (The word periphery comes from the Greek peripheria which means circumference. Plus…) of the tissue). This information will be used to feed mechanical modeling of the behavior of the cornea during intraocular pressure variations (Pressure is a fundamental physical concept. It can be seen as a reported force…) or of the healing process. Finally, the study of pathological tissues will clarify the role of the defective structure of the cornea in the case of certain diseases. These results are published in the journal Light: Science and Applications.
Three-dimensional reconstruction of the lamellar structure of a human cornea. The colors indicate the direction of the collagen lamellae in the imaging plane, as shown in the inset color wheel. The image size is 250 x 250 x 600 µm3. The anterior (side outside the eye) of the cornea is at the top of the image.
References
Unveiling the lamellar structure of the human cornea over its full thickness using polarization-resolved SHG microscopy,
Clothilde Raoux, Anatole Chessel, Pierre Mahou, Gael Latour and Marie-Claire Schanne-Klein,
published August 2, 2023 in Light: Science and Applications.
Doi: 10.1038/s41377-023-01224-0
1693308876
#Map #structure #human #cornea
