Abstract

<b>Introduction:</b>A new treatment of different retinal diseases is the selective photodestruction of the retinal pigment epithelium (RPE) by repetitive us laser pulses sparing the adjacent photoreceptors. This has first been demonstrated in animal experiments by repetivie 5 us and 200 ns laser pulses. In a clinical trail, so far 35 patient with different macular diseases (drusen, diabetis, RCS) were treated with a train of us-laser pulses. Due to the ophthalmoscopic invisibility of the irradiated areas, fluorescein angiography post treatment is necessary to control the therapeutic effect. Subject of this study is development of an On-Line control system to monitor the selective photocoagulation of the retinal pigment epithelium.<b>Material and Methods:</b>In a first attempt, rabbits were treated with a train of 100 laser pulses using a frequency doubled Nd:YLF-laser. Pulse energies between 70-130 µJ and a pulse duration of 1.7 µs were used at a repetition rate of 500 Hz. The eyes were irradiated with a clinical slit lamp and the spot diameter on the retina was 160 µm. Furthermore, the auto fluorescence of patient eyes were measured during treatment. Assuming photocoagulation of the RPE-cell, one possibility for an On-Line detection system is the measurement of the auto fluorescence change during irradiation induced by thermal and mechanical destruction. A strong fluorophore of the RPE is lipofuscin, which excitation wavelength is between 460nm and 540nm and the fluorescence is wide banded between 580nm and 750nm. We use the treatment laser as excitation source. During the single pulse we get 300 kW/cm<sup>2</sup>for excitation. The fluorescence light is coupled out from the excitation light path by using a dichroic beamsplitter inside the slitlamp. The high excitation intensity allowed us to measure the fluorescence with a photodiode.<b>Results:</b>We will present the first in vivo results of our fluorescence measurements on eyes as function of pulse energy for On-Line control of the selective treatment of the retinal pigment epithelium. Other possible methods for on-line control will be discussed.

© 1999 Optical Society of America

PDF Article