Optical properties of human sclera, and their consequences for transscleral laser applications

Abstract

The spectral dependence of the optical properties of human sclera adjacent to the limbus was investigated and related to the potentials of transscleral photocoagulation. The total transmission, absorption, and reflection, as well as the angular distribution of the transmitted and reflected light were measured at five laser wavelengths (442 nm, 514 nm, 633 nm, 804 nm, and 1,064 nm), both for noncontact and contact applications. Absorption and scattering coefficients were determined using the Kubelka-Munk model for light propagation through a scattering tissue. The scleral transmission is only 6% at 442 nm but increases to 35% at 804 nm and to 53% at 1,064 nm. The absorption is high at short wavelengths with 40% at 442 nm but it is only 6% at 804 nm and 1,064 nm. The reflection is generally higher than 40% and shows little wavelength dependence. The transmitted light is scattered diffusely at short wavelengths, but at 804 nm and 1,064 nm it exhibits a fairly narrow angular distribution in forward direction. Fiber contact leads to an increase of transmission, with a factor of 3.5 at 442 nm, of 2.0 at 804 nm, and 1.5 at 1,064 nm. Our results indicate that the diode laser (804 nm) and the Nd:YAG laser (1,064 nm) with contact delivery are best suited for transscleral photocoagulation.

Cyclodestructive Procedures

“…This is shown in figure 3 where the coagulation effects vary considerably at constant irradiation parameters. This could be due to variations in the pressure exerted with the probe in the contact method, differences in thickness or of pigmentation of the sclera [105, 106]and/or due to the sites where the probe is placed on the eyeball and the inclination of the probe [53, 70, 72, 74, 110, 111]. Advanced systems that avoid such problems are described in the section on instrumentation [103].…”

“…Because Nd:YAG laser light (1,064 nm) has by far the best transmittance of any wavelength through the sclera, the Nd:YAG laser may be considered to be the energy source of choice [105, 106], although diode laser light also has good transmission through the sclera.…”

Iris as a reflector for differential absorption low-coherence interferometry to measure glucose level in the anterior chamber

“…31 Meanwhile, the absorption coefficient of glucose at these wavelengths is larger than other substances. 30,[32][33][34][35] In order to reduce the remaining little influence of water and other materials, two possible methods can be considered to solve this problem. One is multivariate calibration techniques [36][37][38] ; the other is to use a closed-loop system.…”

Estudo experimental da aplicação retiniana do laser infravermelho via transescleral sob condições de baixa visibilidade

“…Tentativas experimentais de mensurar as características espectrais de transmissão, absorção e reflexão do LDI na parede ocular, com auxílio de espectrofotômetro têm sido objeto de estudo (4,(7)(8) . Procuramos aternos às características clinicamente detectáveis da permeabilidade escleral, logo após a aplicação do LDI via transescleral.…”

“…Frente às dificuldades inerentes à FRP, à crioterapia e à cirurgia vítreo-retiniana, e cientes da fácil penetração do laser de diodo infravermelho (LDI) através da esclera, realizamos um estudo experimental em olhos de coelhos, comparando o resultado da aplicação do LDI via transpupilar com a transescleral (FRT) (3) . Partimos do princípio que o LDI tem sua eficiência parcialmente dissipada pela parede ocular e procuramos estimar o que denominamos permeabilidade da parede ocular (PPO) à atuação clínica do LDI via transescleral (4) . Tivemos, como objetivo, estabelecer parâmetros de reprodutibilidade e confiabilidade deste procedimento, ainda que realizado sob condições de baixa visibilidade.…”