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 64.3 million in 2013 and projected to be 76 million in 2020.  Glaucoma in Africans tends to be more aggressive and resistant to conventional treatments. Therefore, it was not unexpected when reported that most blindness from glaucoma occurs in Africa.Glaucoma treatment algorithms traditionally entail initial medical therapy followed by laser treatment if medications fail or are inadequate to lower intraocular pressure (IOP) to the desired level. When laser treatment fails, surgery is often then recommended. Although there are several different types of lasers with proven efficacy, glaucoma treatment in Africa, especially in sub-Saharan Africa, largely involves a combination of medication and surgery with little or no availability of the intermediate step of laser treatment. The high cost of glaucoma medication coupled with fear of glaucoma surgery are barriers to adequate glaucoma management in most African countries. 
Generally, any patient diagnosed with primary open angle glaucoma (POAG) may benefit from laser treatment especially when the target IOP cannot be achieved with medical therapy. Recently, it has been shown that selective laser trabeculoplasty is effective as primary treatment when compared to medicines. Other forms of secondary glaucoma such as pseudoexfoliation or pigmentary glaucoma could also benefit from laser trabeculoplasty. However, laser trabeculoplasty is contraindicated in synechial angle closure glaucoma, neovascular glaucoma, patients with corneal opacity, ICE syndrome, and congenital glaucoma. With the improved safety profile of laser cyclophotocoagulation, micropulse transscleral laser therapy is now being used in treating eyes with good vision.
- Adjuvant treatment of POAG
- Primary Treatment of POAG
- Treatment of some secondary open angle glaucomas
- Treatment of refractory glaucomas
- Treatment of failed glaucoma surgery
- Treatment of pediatric glaucoma
- Suture lysis post-trabeculectomy
- Poor compliance with eye drop regimens
- Difficulty using eye drops due to intolerance
Choice of Lasers
This is 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 (SLT) 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
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.,
Selective Laser Trabeculoplasty
Introduced in 1995 this technique uses Q-switched ND-YAG and frequency-doubled ND YAG laser at pulse duration of 10 nanoseconds to 1 microseconds 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.
Micropulse Laser Trabeculoplasty
With this technique 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.
This is the use of laser energy to destroy ciliary processes. The energy absorbed by pigmented epithelium of the ciliary body leads to coagulative necrosis of the tissue and subsequent reduction in aqueous production. Cyclophotocoagulation can be achieved with an Nd-YAG or diode laser. Currently, Diode Laser Cyclophotocoagulation has supplanted Nd-YAG CPC and it can be either Transscleral Diode Laser Cyclophocoagulation (TSCPC) or Endoscopic Cyclophocoagulation (ECP).
Transscleral CPC employs a specifically designed probe contact plate and when placed at the 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 are likely to fail future filtration surgery such as aphakic glaucoma, neovascular glaucoma etc. Transscleral CPC could be performed with either continuous wave or micropulse diode laser.
Continuous Wave Transscleral CPC (CW-TSCPC)
The CW-TSCPC delivers continuous laser energy to the ciliary epithelium. Although it has been shown to be effective in treatment of refractory glaucoma, the reported side effects such as hypotony and phthisis imputed to the continuous laser delivery limits its utility in eyes with good vision.
Micropulse Transscleral Laser Therapy
This improves the safety profile of the procedure in that it releases energy in a form of repetitive pulses on interspersed with pulses off cycle. The off interlude allows the target tissue to cool down and also prevents dissipation of energy to the adjacent tissue.
This involves direct application of the 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.
These recommendations are from the International Council of Ophthalmology (ICO) Guidelines for Glaucoma Care.
|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|
|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|
Selective laser trabeculoplasty has been shown to be effective in IOP reduction, and the percentage of IOP reduction as well as the 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 male and female 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 a 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.
Impact on Anti-Glaucoma Medication
Glaucoma patients incur financial burden as well as side effects as result of prolonged use of anti-glaucoma 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).
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 transscleral cyclophotocoagulation complications include hyptony, decreased vision, phthisis and severe inflammation.
Given the huge annual cost of glaucoma medication in sub-Saharan Africa and the proven efficacy of laser procedures for the treatment of POAG, laser treatments should be encouraged and be made more available and affordable to glaucoma caregivers in Africa.
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