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Forward and backward second harmonic generation imaging of corneal and scleral collagen
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Paper Abstract

Collagen is the most abundant protein in mammalian and forms various types of tissues. On ocular surface, sclera, limbus and cornea are composed with fibril form collagen. However, unlike other connective tissues with high opacity, cornea has extraordinary high transparency which originates from the regular arrangement of collagen fibers within cornea. Cornea is responsible for 80% of focusing power of our vision and any corneal damage can cause severe vision loss. The high transparency of cornea makes it difficult to probe it without invasive processes, especially stromal structure alternations. Collagen, however, is an effective second harmonic generator due to its non-centrosymmetric molecule structure and can be visualized with nonlinear optical process without labeling. In addition, the deeper penetration and point like effective volume of SHG can also provide 3-dimensional information with minimum invasion. Backward SHG imaging has been approved effectively demonstrating structure alternation in infective keratitis, thermal damage in cornea, corneal scar, post refractive surgery wound healing and keratoconus which is also a main complication after refractive surgery[1-6]. In practical, backward SHG has the potentiality to be developed as clinical examination modality. However, Han et al also demonstrated that backward SHG (BSHG) imaging provides collagen bundle information while forward SHG (FSHG) provides more detailed, submicron fibril structure visualization within corneal stroma[7]. In sclera, which also has type I collagen as its main composition, BSHG and FSHG imaging reveal similar morphology. Comparing with what Legare et al demonstrated that BSHG in bulk tissue mainly originate from backscattered FSHG[8], the huge difference between corneal BSHG and FSHG imaging originate from the high transparency of cornea. However, only BSHG could be applied in practical. Therefore, if the correlation of BSHG and FSHG, which reveals more architecture details, can be established, BSHG may be used in clinical examination in the future.

Paper Details

Date Published: 15 February 2008
PDF: 7 pages
Proc. SPIE 6860, Multiphoton Microscopy in the Biomedical Sciences VIII, 68600F (15 February 2008); doi: 10.1117/12.763437
Show Author Affiliations
Wen Lo, National Taiwan Univ. (Taiwan)
Hsin-Yuan Tan, Chang Gung Memorial Hospital (Taiwan)
Institute of Medical Engineering (Taiwan)
Ming-Guo Lin, National Taiwan Univ. (Taiwan)
Chu-Mei Hsueh, National Taiwan Univ. (Taiwan)
Wei-Liang Chen, National Taiwan Univ. (Taiwan)
Sung-Jan Lin, Institute of Medical Engineering (Taiwan)
National Taiwan Univ. Hospital (Taiwan)
Shiou-Hwa Jee, Institute of Medical Engineering (Taiwan)
National Taiwan Univ. Hospital (Taiwan)
Chen-Yuan Dong, National Taiwan Univ. (Taiwan)

Published in SPIE Proceedings Vol. 6860:
Multiphoton Microscopy in the Biomedical Sciences VIII
Ammasi Periasamy; Peter T. C. So, Editor(s)

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