COLA 2015 International Conference on Laser Ablation 2015 31 August – 4 September 2015 Cairns, Australia
PROGRAM HANDBOOK
National Library of Australia Cataloguing-in-Publication entry
2
Creator:
Conference on Laser Ablation (13th : 2015 : Cairns, Qld.)
Title:
Conference on laser ablation 2015 : program handbook / Prof Andrei Rode.
ISBN:
978 0 64694 286 5 (paperback)
Subjects:
1. Laser ablation—Congresses. 2. Lasers—Industrial applications—Congresses.
Other creators/ contributors:
Rode, Andrei.
Dewey number:
621.366
13th Conference on Laser Ablation—COLA-2015 | PROGRAM HANDBOOK
P-074
Optimization of laser-pulse energy during selective laser trabeculoplasty by detection of cavitation bubbles formation P. Gregorčič*1, J. Pribošek1, J. Jakiša1, A. Vrečko2, B. Vedlin2, R. Grčar3, J. Diaci1, J. Možina1 Faculty of Mechanical Engineering, University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, Slovenia 2 Optotek d.o.o., Tehnološki park 21, SI-1000, Ljubljana, Slovenia 3 Eye Clinic Irman, Savinjska cesta 2, 3310 Žalec, Slovenia E-mail:
[email protected]
1
The selective laser trabeculoplasty (SLT) is a pulse-laser treatment for the reduction of intraocular pressure in eyes with open angle glaucoma and ocular hypertension [1]. It was introduced by Latina and Park [2], who demonstrated the possibility of selective targeting of the pigmented trabecular meshwork cells by using a Qswitched frequency-doubled Nd:YAG laser with low fluences. This enables treatment without producing collateral damage to the adjacent non-pigmented eye cells and tissues. Moreover, in comparison with an older technique, called argon laser trabeculoplasty [3], the SLT method does not cause coagulation of the trabecular tissue. Instead, the selective absorption in melanin stimulates and facilitates draining of aqueous humour. The trabecular meshwork cells contain melanin granules, which absorb visible light. This absorption in the pigment turns the absorbed laser-pulse energy in a local rise of the tissue temperature. In such a way, the fluid is vaporized on the surface of melanin granules and therefore micro-meter (transient intracellular) cavitation bubbles are formed around the laser-irradiated cells containing the pigment [4]. By increasing the laser-pulse energy the radius of these bubbles grows to the dimensions, when they become visible by ophthalmoscopy. The cavitation bubbles induced by selective absorption of the laser pulse represent a kind of microscopic underwater explosions leading to cavitation damage. The cavitation damage is confined to the scale of single cells containing the pigment only when pulse energy is low enough to produce bubbles that are only few micrometers in size [5]. Consequently, proper setting of the laser energy is essential for ensuring that the target cells are successfully and selectively treated without creating excess damage to the tissue. To ensure this, the operation protocol of SLT is as follows. The spot size is fixed during the entire treatment (typically 400 m), while laser pulses have wavelength of 532 nm and are shorter than 5 ns. The treatment starts with low energy (typically 0.8 mJ) and it is increased or decreased by an increment of 0.1 mJ until the threshold energy is achieved [6]. The threshold energy is defined as the energy, where the ophthalmologist visually recognizes the formation of cavitation bubbles by ophthalmoscopy. When bubbles are visually detected, the operating surgeon lowers the laser energy just below the threshold for bubbles’ formation. In such a way the ophthalmologist subjectively regulates the laser energy during the operation. Since an automatic method to monitor the bubbles’ formation can make the SLT process more reliable and less time consuming [5], we have developed an automatic detection of cavitation bubbles formation on the patient’s eye [7]. In this contribution we will present ex-vivo and in-vivo experiments, the optical system for image acquisition and the solution for image processing that enable us to develop the automatic adjustment of the laser-pulse energy during the treatment. This allows the execution of the procedure closer to the threshold for the cavitation bubble’s formation, thereby making the entire procedure more reproducible and effective.
1 2 3 4 5 6 7
J. M. Shi and S. B. Jia, “Selective laser trabeculoplasty,” Int. J. Ophthalmol. 5, 742 (2012). M. A. Latina and C. Park, “Selective Targeting of Trabecular Meshwork Cells - in-Vitro Studies of Pulsed and CW Laser Interactions,” Exp. Eye Res. 60, 359 (1995). A. M. Bovell, K. F. Damji, W. G. Hodge, W. J. Rock, R. R. Buhrmann, and Y. I. Pan, “Long term effects on the lowering of intraocular pressure: selective laser or argon laser trabeculoplasty?” Can. J. Ophthalmol. 46, 408 (2011). C. P. Lin and M. W. Kelly, “Cavitation and acoustic emission around laser-heated microparticles,” Appl. Phys. Lett. 72, 2800 (1998). C. P. Lin, “Selective absorption by melanin granules and selective cell targeting” in, Lasers in Ophthalmology – Basic, Diagnostic and Surgical Aspects: a Review, F. Fankhauser and S. Kwasniewska ed. (Kugler Publications, The Hague, 2003). M. A. Latina and D. H. Gosiengfiao, “Selective laser trabeculoplasty,” in, Lasers in Ophthalmology – Basic, Diagnostic and Surgical Aspects: a Review, F. Fankhauser and S. Kwasniewska ed. (Kugler Publications, The Hague, 2003). A. Vrečko, B. Vedlin. J. Jakiša, P. Gregorčič, “Ophthalmic laser device,” EU patent application (2014).
