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Editors Selection IGR 15-1
Anatomical Structures: Trabecular meshwork
Comment by James Tan on:
52485 Direct trabecular meshwork imaging in porcine eyes through multiphoton gonioscopy, Masihzadeh O; Ammar DA; Kahook MY et al., Journal of biomedical Optics, 2013; 18: 036009
Mashizedeh et al. describe novel methodology to visualize iridocorneal angle structures by multiphoton microscopy (MPM) through a gonioscopic lens. MPM uses femtosecondpulsed, near-infrared laser that permits tissue and cellular imaging with less scatter, absorption and phototoxicity than with conventional single photon microscopy. High-resolution deep-tissue optical sectioning is possible, potentially with no light-induced damage. Application of the technique has grown rapidly in live animal research, and it is evolving as a promising diagnostic tool in several clinical disciplines. The novel step here concerns adapting MPM optics to provide a long working distance commensurate with imaging across the anterior chamber through a gonioscopic lens. This allows the trabecular meshwork (TM) to be imaged through an optically clear cornea rather than transsclerally, aiming to reduce MPM signal degradation. Application of the approach is illustrated in a postmortem pig eye ex vivo. A montage of 2D images revealed a mesh-like structure resembling the (inner) uveal and perhaps corneoscleral meshwork. The images combined two MPM modalities: fluorescence excitation, leading to autofluorescence from proteins such as elastin, collagen and melanin; and second harmonic generation (SHG), in which detection of specific photon scattering and recombination is traceable to certain proteins, in this case collagen. Superimposition of signals from different modalities provided information not just on angle microstructure, but also biological composition. Autofluorescence was interpreted to originate from iris and TM melanin, and SHG from collagenous beams.
The method described represents a potentially useful approach for imaging the aqueous drainage route by the powerful technique of MPM. Further technical development may entail optimizing resolution to visualize greater structural detail and cells. Achieving deeper tissue penetration to see critical drainage regions of juxtacannalicular meshwork and Schlemm's canal would be a significant advance. The authors have used an innovative approach to move toward these goals and ought to be congratulated.
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