MACHO 16

Eye Department KCMC Newsletter

Issue 2 Volume 5 Serial 16                                                                               30 June 2015

Selective Laser Trabeculoplasty

Glaucoma is the leading cause world wide if irreversible blindness. This is a disease whereby the optic nerve head is damaged by raised intraocular pressure. The optic nerve is the convergence of the nerves originating from the photoreceptors of the retina in their path towards the visual cortex; their function is to deliver the visual stimulus to the brain for interpretation. In case of raised intraocular pressure, the individual axons are damaged at the level of the lamina cribrosa of the optic nerve head, as the histioarchitecture renders this spot with inherent weakness. In primary open angle glaucoma the cause for raised intraocular pressure is resistance to outflow at the trabecular meshwork.

As glaucoma progresses, the visual field of the patient is constricted or develops islands of defect, however vision remains normal. This means that the patient will be unaware that they are gradually loosing their visual function. The triad of glaucoma includes:

1. Measurement of Intraocular Pressure (Normal is 9 – 21 mmHg)

2. Evaluation of the Optic Nerve Head Excavation (Normal is less than 0.8)

3. Visual Field Test

Glaucoma treatment includes medical and surgical approaches. Most of the patients will be put on intraocular pressure lowering eye drops initially, such as Timolol 0.5%, Brimonidine 0.2%, Dorzolamide 2% or Latanoprost 0.005%. In some patients one type of eye drops or several combinations of eye drops are enough to control the disease. Disease control is assessed by annual visual field tests to evaluate progress. Sometimes intraocular pressure readings alone are an indicator enough of progress.

Trabeculectomy is the standard surgical procedure when medical treatment is not effective in controlling the intraocular pressure. This procedure constitutes creation of a fistula between that anterior chamber and the sub-tenons space. Most of the complications arising from trabeculectomies are caused either by over filtration in the first few days or failure due to the bodies inherent repair processes. Other surgical options include trabeculotomy, goniotomy for children and synthetic drainage valves such as Ahmed Valve, Molteno Valve and Express Shunt.

Diode laser is used in Cyclophotocoagulation of the ciliary body in cases of a painful blind eye or in case other surgical procedures can not be done. Argon Laser Trabeculoplasty is used to lower the intraocular pressure by causing photocoagulation of the trabecular meshwork, causing contraction of tissue and opening of channels.

Selective Laser Trabeculoplasty is a 532nm frequency double YAG laser that is applied to the trabecular meshwork, its mechanism of action is not clear, however the impact is reduction of intraocular pressure. The hypothesis is that the laser induces cell division, release of mediators of inflammation which restore the trabecular meshwork function. Some 100 spots of laser can be applied to the trabecular meshwork and the process may be repeated more than once. A special goniolens is needed to visualize and treat the trabecular meshwork in the chamber angle. The response rate to treatment varies between 58% – 94% in year one and plummets to 31% - 58% after 5 years. Given that it is administrered once or twice and may buy up to five years of slowing down glaucoma progression it is a positive development. The high cost of the laser machine remains a challenge. The Eye Department is lucky in having this important therapeutic tool that is expected to impact positively in the glaucoma management.

Dr Heiko Philippin, the Glaucoma Specialist treating a patient with the SLT

Editor: W. Makupa, Eye Department KCMC, P.O.Box 3010 Moshi – Tanzania

Tel: +255 784 332 667 Fax: +255 27 275 4381 Email: makupauw@yahoo.com