Primary Open Angle Glaucoma in Africa: Prospects and Application of Lasers in African Eyes
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Glaucoma is the leading cause of irreversible blindness in the world. The number of people living with glaucoma was estimated to be 64.3million in 2013 and projected that by 2020, the figure will increase to 76.0 million.  Glaucoma in Africans tend to be more aggressive and resistant to conventional treatments. Therefore, it was not unexpected when reported that most of glaucoma blindness occurs in Africa.Glaucoma treatment algorithm traditionally entails initial medical therapy to be followed by laser if medications fail or are inadequate to lower intra-ocular pressure to desired level. When laser fails, surgery is then recommended. Although there are different types of lasers with proven efficacy against glaucoma, treatment of glaucoma in Africa especially the sub-Saharan Africa largely involves the duo of medication and surgery with little or no availability of the intermediate laser treatment. High cost of anti- glaucoma medication coupled with fear of glaucoma surgery are the bane of glaucoma management in most African countries. Therefore, lasers, being less invasive and portable, offer glimmer of hope for glaucoma care in Africa.
Generally, any patient diagnosed with POAG could benefit from laser treatment especially where target intra-ocular pressure (IOP) could not be achieved with maximum medical therapy. Recently, it has been shown that Selective Laser Trabeculoplasty is effective as primary treatment as such it could be used as primary intervention. Others forms of secondary glaucomas such as pseudo exfoliation or pigmentary glaucoma could also benefit from laser trabeculoplasty. However, Laser Trabeculoplasty is contraindicated in synechial Angle closure glaucoma, NVG, patients with corneal opacity, ICE syndrome and congenital glaucoma.With improved safety profile of laser cyclophotocoagulation, micropulse trans-scleral laser therapy is now being used in treating eyes with good vision.
1.Adjuvant treatment of POAG
2.Primary Treatment of POAG
3.Treatment of some secondary open angle glaucoma
4.Treatment of refractory glaucoma
5.Treatment of failed glaucoma surgery
6.Treatment of pediatric glaucoma
8.Poor compliance with eye drop regimens
9.Difficulty using eye drops due to intolerance== Contraindications ==
CHOICE OF LASERS
1.Laser trabeculoplasty defined as application of laser to trabecular meshwork in order to improve facility of aqueous outflow. Wiser and Witter in 1979 introduced Argon Laser Trabeculoplasty(ALT) while Latina and Park described selective laser trabeculoplasty (ALT) in 1995. Several studies have demonstrated the efficacy and safety of the two procedures. Micropulse Laser Trabeculoplasty(MLT) is the newest addition into the armamentarium
A. Argon Laser Trabeculoplasty (ALT): This was first introduced in 1979 and it involves application of CW 514nm argon green or blue-green laser at the junction between the pigmented and non-pigmented portion of the trabecular meshwork. ALT brings about IOP reduction via creating some mechanical changes in trabecular meshwork that subsequently open up the drainage pathway or by stimulating biological activity in trabecular cells that leads to IOP reduction. The safety and efficacy of the laser has been reported in several studies.,
B. Selective Laser Trabeculoplasty introduced in 1995 uses Q-switched ND-YAG and frequency-doubled ND YAG laser at pulse duration of 10 nanosec to 1 microsec selectively targeting pigmented portion of trabecular meshwork without collateral damage to adjacent tissues. SLT is thought to reduce IOP by stimulating cascade of cellular activities in trabecular meshwork that ultimately leads to increase facility of aqueous outflow.
C. Micropulse Laser Trabeculoplasty: This relatively new techniques, instead of delivering the laser energy in a continuous wave, the energy is subdivided into short pulses with specific “on” and “off” times thereby minimizing the heat buildup and hence thermal damage to adjacent tissues. The off interlude allows the temperature of the target tissue to cool down before the next shot .It also fend off spread of energy to adjacent tissue.
2. Laser cyclophotocoagulation refers to the use of laser energy to destroy ciliary processes. The energy absorbed by pigmented epithelium of ciliary body leads to coagulative necrosis of the tissue and subsequent reduction in aqueous production. Cyclophotocoagulation can be achieved with Nd-YAG or Diode laser. Currently, Diode Laser Cyclophotocoagulation has supplanted Nd-YAG CPC and it can be either Trans-scleral Diode Laser Cyclophocoagulation (TSCPC) or Endoscopic Cyclophocoagulation (ECP).
A. Trans-scleral CPC :Trans-scleral CPC employs specifically designed probe contact plate which when placed at appropriate distance from the limbus ensures delivery of energy into the ciliary processes. Laser CPC is a treatment of last resort reserved for glaucoma unresponsive to maximum medical treatment, eyes that have failed filtration surgery or likely to fail future filtration surgery such Aphakic glaucoma, Neovascular glaucoma etc. Trans-scleral CPC could be performed with either continuous wave or Micropulse diode laser.
1.Continuous Wave Trans-scleral CPC (CW-TSCPC):The CW-TSCPC delivers continuously laser energy to the ciliary epithelium. Although it has been shown to be effective in treatment of refractory glaucoma, the reported deleterious side- effects such as hypotony and phthisis imputed to continuous laser delivery limited its utility in eyes with good vision.
2. Micropulse Trans-scleral Laser Therapy improves the safety profile of the procedure in that it releases energy in a form of repetitive pulses(on) interspersed with off cycle. The off interlude allows the target tissue to cool down and also prevent dissipation of energy to the adjacent tissue.
B. Endoscopic Cyclophotocoagulation involves direct application of laser to the targeted ciliary pigmented epithelium with little or no collateral damage to the adjacent ciliary muscle, ciliary body stroma or par plana and it can be combined with cataract surgery.
|Treatment Parameters||Argon Laser Trabeculoplasty||Selective Laser Trabeculoplasty|
|Laser type||Argon green or Blue green/Diode Laser||Frequency doubled Q-Switched Nd:YaG Laser(532nm)|
|Spot size||50 microns (Argon) or 75 microns (Diode)||40 microns|
|Power||300 to 1000mW||0.5 to 2mJ|
|Application site||TM junction non-pigmented/pigment||Trabecular meshwork (TM)|
|Handheld Lens||Goldmann gonioscopy lens or Ritch lens||Goldman or SLT lens|
|Number of Burns||50 per 180 degrees||50 per 180 degrees|
|Number of Settings||1 or 2|
|End points||Blanching at junction of anterior non-pigmented and pigmented TM|
*copied from ICO guidelines for glaucoma care
Cyclophotoocoagulation for Glaucoma: International Recommendations**
|Treatment Parameters||Transscleral Diode Laser|
|Laser Type||Diode Laser|
|Power||1.0 to 2.5 W|
|Exposure Time||0.5 to 4.0 seconds|
|Application Site||1.0 to 2.0 mm from limbus|
|Handheld Probe||Transscleral contact|
|Treated Circumference||180 – 360 degrees|
|Number of Burns||~ 12 – 20 spots per 180 degrees|
|Number of Sittings||1 or 2|
**copied from ICO guidelines for glaucoma care
1.IOP Reduction: Selective Laser trabeculoplasty has been shown to be effective in IOP reduction and the percentage IOP reduction as well as mean IOP decrease varies between studies., In South Africa, Goosen et al reported 32.0% (20mmHg to 13.6mmHg) IOP reduction from baseline and observed no difference in response between males and females patients. Similarly, Seck et al retrospectively reviewed 69 eyes of 40 black patients 12 months after treatment with SLT. The results showed that 90% of patients had mean IOP decrease of 2.3 ± 1 mmHg and SLT permitted discontinuation of a prostaglandin in 60% (42 cases). Similarly, Micropulse Laser Trabeculoplasty has also been shown to cause 17.2% reduction from baseline among Nigerian eyes.
2.Impact on Anti-Glaucoma Medication: Glaucoma patients incur financial burden as well as side-effects as result of prolonged use of antiglaucoma medication. Ahmed et al  found significant reduction in anti-glaucoma medication from 2.25 ± 0.97 before SLT treatment to 1.0 (±1.3) at the end of 18 months follow-up (P= 0.004).
3.Laser as Primary Treatment: The seminal LiGHT trial, though not conducted on African eyes, described how target intraocular pressure was achieved without intraocular pressure medication in 419 (78·2%) of 536 eyes treated with selective laser trabeculoplasty as primary treatment. Additionally, in Nigeria, Abdul et al demonstrated that 83% of POAG had a drop in IOP of >30% at 12 months after primary treatment with continuous trans-scleral cyclophotocoagulation and only 9% were on medication at the final follow up.
Complications associated with laser trabeculoplasty include acute IOP elevation, uveitis, peripheral anterior synechia, corneal burns and hyphema while trans-scleral cyclophotocoagulation could be complicated by hyptony, drop in vision, phthisis and severe inflammation.
Conclusion: With huge annual cost of glaucoma medication in sub-Saharan Africa and proven efficacy of laser procedures in treatment of PAOG, laser treatments should be encouraged and be made more available and affordable to glaucoma care- givers in Africa.
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