Dr Brian Ang
The Royal Victorian Eye and Ear Hospital, Melbourne Eye Specialists
Glaucoma is a leading cause of blindness worldwide and a major public health concern. As intraocular pressure (IOP) is an important modifiable risk factor for the development and progression of glaucoma,1-3 much of glaucoma management is focused on lowering IOP to reduce the risk of optic nerve damage and subsequent vision loss.
IOP control can be achieved via medication (Table 1), laser or surgery. The effect of laser trabeculoplasty is impermanent, and surgery is generally considered only if the IOP remains elevated or if the glaucoma continues to progress despite maximum tolerated medical therapy. The great majority of glaucoma patients can expect to be on at least one topical IOP-lowering medication at some point in the course of their glaucoma management.
Table 1. Classes of intraocular pressure lowering medications
How difficult can it be to treat a glaucoma patient medically? In theory, it sounds easy. Prescribe the patient with a topical IOP-lowering medication and after four to six weeks, the IOP should be reduced. In reality, there are numerous important issues that need to be considered before deciding on the type of glaucoma medication to use, or indeed, even whether glaucoma medication is appropriate for that particular patient.
There are seven considerations that clinicians should address when managing a glaucoma patient medically.
- Confirm glaucoma and exclude other pathology
First and foremost, the patient should have the diagnosis of glaucoma confirmed before starting treatment. Not all optic disc cupping and visual field loss are due to glaucoma. Any clinical feature that does not seem typical for glaucoma—such as neuroretinal rim pallor, reduced colour vision, or bilateral field defect that obeys the vertical meridian—needs to be investigated further. A misdiagnosis of glaucoma and consequent missed diagnosis of other ocular or neurological condition, which may coexist with the glaucoma, can be potentially disastrous for the patient.
- Exclude angle closure in all glaucoma patients
Originally thought to be a condition primarily affecting Asian populations, angle closure is now increasingly recognised as a significant cause of glaucoma in Caucasian populations as well.4 In patients with angle closure glaucoma, medication alone will be insufficient to lower IOP because the underlying cause of angle closure also requires treatment. Depending on the mechanism of angle closure, treatment options may include laser iridotomy, laser iridoplasty or cataract surgery.
It is essential that all suspected glaucoma patients be assessed for angle closure with gonioscopy and/or anterior segment optical coherence tomography imaging in dark conditions.
- Decide on appropriateness of eye-drops
Once the diagnosis of glaucoma has been confirmed and angle closure has been excluded, the next issue to consider is the appropriateness of eye-drops as primary treatment. Selective laser trabeculoplasty (SLT) has been shown to be as effective as latanoprost in lowering IOP over a 12-month period,5 with repeat treatments reported to be safe and as efficacious as the primary treatment.6
Depending on personal or social circumstances, SLT may be more appropriate as primary treatment compared to topical medication for certain patient groups, such as pregnant women and arthritic patients who are unable to squeeze the eye-drop bottles.
- Be aware of local and systemic side-effects
All medications, even topical eye-drops, have the potential to cause local and/or systemic side-effects. Local side-effects include eyelash growth and periorbital skin pigmentation with prostaglandin analogues, allergic dermatitis with brimonidine, and corneal decompensation with carbonic anhydrase inhibitors.
Systemic side-effects include bronchospasm and postural hypotension with beta-adrenergic antagonists, respiratory depression with brimonidine, and confusion with pilocarpine. These effects can cause significant morbidity in elderly patients.7 Patients need to be asked and be made aware of the potential side-effects to reduce the risk of suffering medication harm.
- Reduce risk of side-effects
When patients are prescribed with glaucoma eye-drops, they are effectively being asked to experience potential side effects over the long term to control a generally asymptomatic disease that may or may not result in blindness in their lifetime. By decreasing the side-effects, the likelihood of patient adherence to medication is enhanced.
Side-effects can be minimised by limiting the amount of eye-drops used, using lower concentration preparations, switching rather than adding drops, and using combination preparations where possible. Digital occlusion of the nasolacrimal ducts for one to two minutes following drop instillation can also decrease systemic absorption and side-effects.
- Be aware of toxicity from preservatives
Preservatives in eye-drops, such as benzylkonium chloride, are essential to prevent microbial colonisation; however, these preservatives also significantly worsen the symptoms of ocular surface disease commonly experienced by many glaucoma patients.8 The ideal would be to use preservative-free drops, such as tafluprost and preservative-free bimatoprost, where possible. Preservative toxicity can also be reduced by using preparations with gentler preservatives that do not contain benzylkonium chloride.
- Emphasise importance of compliance
Ultimately, the success or failure of treatment depends on whether the patient uses the glaucoma medications as prescribed. Poor compliance is associated with higher IOP, progressing glaucoma, unnecessary changes to treatment, and increased health-care costs.9 Regularly ask patients about how often they forget or neglect to use their eye-drops. If a patient is non-compliant with treatment, try to ascertain the underlying reason(s). These can vary from cost and medication side-effects to difficulty with the eye-drop bottle, poor understanding of treatment, and plain forgetfulness. Strategies to deal with non-compliance should encompass acknowledging the patient’s difficulties, explaining the importance and rationale for treatment (with the help of an interpreter or family member if necessary), clearly writing down the eye-drop regime, and working out a mutually acceptable solution.
The guiding principle when managing glaucoma patients should always be: First do no harm. Medical treatment has the potential to cause harm through wrong diagnosis, inappropriate choice of medication, and local and systemic side-effects, as well as under- and over-treatment.
It is up to the clinician to ensure that the risk of harm from glaucoma treatment is far outweighed by the risk of harm from the glaucoma itself.
- Kass MA, Heuer DK, Higginbotham EJ et al. The Ocular Hypertension Treatment Study: a randomized trial determines that topical ocular hypotensive medication delays or prevents the onset of primary open-angle glaucoma. Arch Ophthalmol 2002; 120: 701-713.
- Heijl A, Leske MC, Bengtsson B et al. Early Manifest Glaucoma Trial Group. Reduction of intraocular pressure and glaucoma progression: results from the early Manifest Glaucoma Trial. Arch Ophthalmol 2002; 120: 1268-1279.
- The AGIS Investigators. The Advanced Glaucoma Intervention Study (AGIS): 7, the relationship between control of intraocular pressure and visual field deterioration. Am J Ophthalmol 2000; 130: 429-440.
- Ng WS, Ang GS, Azuara-Blanco A. Primary angle closure glaucoma: a descriptive study in Scottish Caucasians. Clin Exp Ophthalmol 2008; 36: 847-851.
- Nagar M, Ogunyomade A, O’Brart D et al. A randomised, prospective study comparing selective laser trabeculoplasty with latanoprost for the control of intraocular pressure in ocular hypertension and open angle glaucoma. Br J Ophthalmol 2005; 89: 1413-1417.
- Avery N, Ang GS, Nicholas S et al. Repeatability of primary selective laser trabeculoplasty in patients with primary open-angle glaucoma. Int Ophthalmol 2013; 33: 501-506.
- Diggory P, Cassels-Brown A, Vail A et al. Avoiding unsuspected respiratory side-effects of topical timolol with cardioselective or sympathomimetic agents. Lancet 1995; 345: 1604-1606.
- Fechtner RD, Godfrey DG, Budenz D et al. Prevalence of ocular surface complaints in patients with glaucoma using topical intraocular pressure-lowering medications. Cornea 2010; 29: 618-621.
- Konstas AG, Maskalers G, Gratsonidis S et al. Compliance and viewpoint of glaucoma in Greece. Eye 2000; 14: 752-756.