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Abstract #5581 Published in IGR 2-1
Optical properties of human trabecular meshwork in the visible and near-infrared region
Farrar SK; Roberts C; Johnston WM; Weber PALasers in Surgery and Medicine 1999; 25:348-362
BACKGROUND AND OBJECTIVES: Despite disparate treatment parameters, similar success in laser trabeculoplasty (LT) is attained using the argon (514.5 nm) and diode (810 nm) laser. However, the mechanism of this success remains unresolved. To further understand LT, this study characterizes the optical properties of trabecular meshwork (TM). STUDY DESIGN/MATERIALS AND METHODS: Reflectance was measured from ten TM samples over wavelengths of 400-820 nm, using an integrating sphere/spectrophotometer. Corrections were made for reflections at boundaries of refractive index mismatch. Kubelka-Munk coefficients were calculated and converted to linear transport coefficients. RESULTS: Scattering greatly dominated absorption. The scattering and absorption coefficients were, respectively, 141.20±15.80 cm-1 and 4.89±1.95 cm-1 at 514.5 nm, and 94.44±15.03 cm-1 and 0.0874±0.111 cm-1 at 810 nm (estimated anisotropy of 0.90). The corresponding penetration depths (1/e) were 69 μm (514.5 nm) and 106 μm (810 nm). CONCLUSIONS: The absorption coefficient of 514 nm energy is two orders of magnitude greater than 810 nm energy, while scattering coefficients are much closer. The fluence used at 514.5 nm is higher at the surface than that at 810 nm, but falls below it deep within the TM due to the differential absorption. Therefore, similar initial therapeutic effects are obtained with 810 nm using less total absorbed energy. Thermal damage resultant from excess energy deposited at 514.5 nm may be related to the lack of success in repeat argon LT, pointing out the need for studies of repeat diode LT.
Dr. S.K. Farrar, Biomedical Engineering Center, Ohio State University, Columbus, OH 43210, USA
Classification:
2.5 Meshwork (Part of: 2 Anatomical structures in glaucoma)
12.4 Laser trabeculoplasty and other laser treatment of the angle (Part of: 12 Surgical treatment)
