Optical properties of human trabecular meshwork in the visible and near-infrared region

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 10 TRI sa mples over wavelengths of 400-820 nm, using an integrating sphere/spectroph otometer. 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 absorp tion 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 penetratio n depths (1/e) were 69 mu m (514.5 nm) and 106 mu m (810 nm). Conclusion: The absorption coefficient of 514 nm energy is two orders of ma gnitude greater than 810 nm energy, while scattering coefficients are much closer. The fluence used at 514.5 ma is higher at the surface than that at 810 nm, but falls below it deep within the TM: due to the differential abso rption. Therefore, similar initial therapeutic effects are obtained with 81 0 nm using less total absorbed energy, Thermal damage resultant from excess energy deposited at 514.5 mn may be related to the lack of success in repe at argon LT, pointing out the need for studies of repeal diode LT. (C) 1999 Wiley-Liss, Inc.