Clinical Drug Experience Knowledgebase

A debate continues concerning best first-line therapy for African primary open angle glaucoma. Most African practitioners advocate first line trabeculectomy surgery yet most frequently practice first line drug therapy because of patient acceptance and other issues. In the developed world a range of first line therapies including drug, SLT, cyclodiode ciliary body ablation, trabeculectomy surgery, drainage tube surgery and other drainage procedures (viscocanalostomy, non-penetrating surgery etc) have been advocated.

There is a paucity of good evidence concerning the relative merits of these approaches in an African context. The purpose of this study is to compare two approaches to first line therapy of primary open angle glaucoma in an African population.

Design A two centre randomised prospective trial of SLT vs. prostaglandin analogue first line therapy for primary open angle glaucoma.

Methods African patients with established or newly diagnosed primary open angle glaucoma or patients with POAG currently on single drug therapy (excluding prostaglandin analogues) and elevated IOP are recruited in Innovation Eye Centre in Kisii, Kenya and McCord Hospital, University of KwaZulu-Natal, Durban, South Africa. While if clinically indicated both eyes will be treated, one eye per patient to be included in the study.

After informed consent all patients undergo a standardised examination to establish baseline ocular function and findings. All patients receive counselling in glaucoma, the disease, what it means and the therapy. The patient is then randomised (randomisation in London, contained in sealed opaque envelopes) to receive SLT or prostaglandin analogue therapy. Every effort is made to follow all patients according to a standardised protocol at a minimum of month 3, month 6 and month 12. All therapeutic failures are followed closely to ascertain further management plans and subsequent therapeutic compliance. Follow-up is offered beyond 12 months.

Medical therapy Those randomised to medical therapy patients receive free Prostaglandin analogue in KZN or in Innovation Eye Centre with counselling on drop instillation and instructions for renewal of their prescription. Prescription renewal is to be free of charge.. An appointment is given for review in 3 months. Considerable attention is being paid to estimating compliance including the use of bottle weighing and questionnaires already developed and used locally.

SLT THERAPY Those randomised to SLT will receive counseling on the effects and management of SLT.

System: Selecta II (Lumenis) - Frequency doubled Nd: YAG (532nm) Pre-Laser Treatment

Topical anesthesia (e.g. proxymetacaine hydrochloride)
Prophylactic application of alpha agonist or equivalent agent (e.g. brimonidine) to avoid
Post-op pressure spike

Laser Treatment parameters:

Duration 3ns (preset)
Spot size 400µ (preset)
Number of applications: 100
Extent of angle: 360 degree

Power (dependent on angle pigmentation)

If pigmentation is 1 or 2. start at 0.8 mJ and adjust power in 0.1 mJ increments until visible response (cavitation bubbles - colloquially referred to as "champagne bubbles")
If pigment grade is 3 or 4, start at lower energy 0.4 mJ and adjust power in 0.1 mJ increments until visible response
When reaching the treatment endpoint (cavitation bubbles), scale down the energy level by 0.1 mJ and remain on that threshold throughout treatment
It is recommended to re-evaluate threshold following the treatment of each quadrant, due to variations in TM pigmentation to reach treatment endpoint (cavitation bubbles) Post-Laser Treatment
Patient's IOP follow up - one hour post treatment
NSAIDS up to 2-3 days post-op, or depending on the level of patient discomfort
It is not recommended to prescribe steroidal medication as it may potentially interfere with the SLT mechanism of action.

Follow-up At 3 months Patients will have a structured questionnaire relating to any adverse effects from the therapeutic interventions. They will receive an examination of visual function, external ocular structures and intraocular pressure in addition to the optic nerve head.

Those with unacceptable topical/systemic side effects and those with partial or complete failure of IOP control (see outcomes) will have secondary therapy commenced in the form of timolol 0.5% or, if contraindicated, either brimonidine or oral acetazolamide)). The secondary therapy will either replace or be additive to the primary therapy depending on the initial response.

At 6 months Patients will have a structured questionnaire relating to any adverse effects from therapeutic interventions. They will receive and examination of visual function, external ocular stuctures and intraocular pressure in addition to the optic nerve head.

Those with unacceptable topical/systemic side effects and those with partial or complete failure of IOP control (see outcomes) will have secondary or tertiary therapy commenced in the form of timolol 0.5% or, if contraindicated, either brimonidine or oral acetazolamide)) or surgical intervention in the form of a trabeculectomy with cytotoxic.

At 12 months Patients will have a structured questionnaire relating to any adverse effects from therapeutic interventions. This questionnaire will also include questions relating to their acceptance of the therapy and view of the therapy. They will receive a detailed examination of visual function and ocular parameters.

Those with unacceptable topical/systemic side effects and those with partial or complete failure of IOP control (see outcomes) and those with evidence of glaucoma progression will have secondary or tertiary therapy commenced in the form of timolol 0.5% or, if contraindicated, either brimonidine or oral acetazolamide)) or surgical intervention in the form of a trabeculectomy with cytotoxic.