Glaucoma

Risk factors

Risk factors for the development of glaucoma include:

• High intraocular (eye) pressure (IOP)
• Ethnicity
• Increasing age, and
• Positive family history for glaucoma and ethnicity.

IOP

Although elevated IOP is the major risk factor for glaucoma, the condition is not considered to be a direct consequence of the pressure, but to relate to IOP-associated risk factors such as stress susceptibility of the optic nerve supporting structures and optic nerve blood flow, that are affected by IOP.

Certain individuals can sustain a degree of IOP elevation without the development of glaucoma and are referred to as having ocular hypertension, although as a group such individuals remain at increased risk of developing glaucoma with time.

Ethnicity

POAG is most common in white Caucasians and black individuals of African origin. PACG is most common in South-East Asians and worldwide about 33% of individuals with primary glaucoma have PACG. PACG is associated with a greater risk of blindness in comparison with POAG.

Angle closure glaucoma

Small eye size (low axial length, often associated with a hypermetropic refraction) and other anatomical or pathophysiological ocular features that increase the risk of pupil-block (increased resistance to flow of aqueous from the posterior to anterior chamber), are the major risk factors for PACG.

Impact

Glaucoma is the third leading cause of blindness and the fourth leading cause of all vision loss worldwide. It is thought that at present at least 3 million people are blind and 4 million experience moderate to severe vision impairment due to glaucoma (Adelson et al., 2020).

However, most forms of glaucoma do not show symptoms in the early stages and thus patients often present for treatment only after vision loss has occurred.

This means the number of people with glaucoma is much larger than those with vision loss due to glaucoma. It has been estimated that by 2020 there were 76 million people with glaucoma, rising to 112 million in 2040 (Tham et al., 2014).

These figures are set to rise, unless improved screening and effective treatment strategies are successful.

Treatment and successes

Treatments, which include medication, laser treatment and surgical interventions, cannot restore lost sight but are able to preserve the patient’s remaining visual function.

Primary open angle glaucoma

The mainstay of treatment for primary open angle glaucoma involves reducing IOP by 20-40%, which can be achieved using medical, laser or surgical strategies.

• At present most treated patients are prescribed topical medications. Availability and persistent adherence to topical medications remains a significant problem and side effects both local and systemic can limit their use.
• Laser treatment of the trabecular meshwork (eg selective laser trabeculoplasty) is virtually free of adverse effects, but long-term effectiveness has yet to be determined and lasers are not available throughout all countries.
• There are a variety of highly successful surgical procedures to lower IOP, but risks are higher in comparison with non-surgical treatments, so that surgery has not become a popular initial strategy in the management of glaucoma.

At present management choices throughout the world depend on availability of the various therapeutic modalities, this correlating highly with the socioeconomic status of the country.

Primary angle closure glaucoma

The mainstay of treatment for (or prevention of) PACG is the provision of a peripheral laser iridotomy or surgical iridectomy (ie a hole in the iris that connects the posterior and anterior chambers, so bypassing any potential, or established, pupil block to aqueous flow).

References

• Quigley HA. Glaucoma. Lancet 2011;377:1367-77.
• Flaxman SR. Global causes of blindness and distance vision impairment 1990–2020: a systematic review and meta-analysis 2017; https://doi.org/10.1016/S2214-109X(17)30393-5
• Foster PJ et al. The definition and classification of glaucoma in prevalence surveys. Br J Ophthalmol 2002;86:238-42.
• Leske MC. Open-angle glaucoma – an epidemiologic overview. Ophthalmic Epidemiol 2007;14:166-72.
• Heijl A et al. Natural history of open-angle glaucoma. Ophthalmology 2009;116:2271-6.
• Collaborative Normal-Tension Glaucoma Study Group. Comparison of glaucomatous progression between untreated patients with normal-tension glaucoma and patients with therapeutically reduced intraocular pressures. Am J Ophthalmol 1998;126:487–97.
• Foster PJ & Johnson GJ. Glaucoma in China: how big is the problem? Br J Ophthalmol 2001; 85: 1277–82.
• Yip JLY & Foster PJ. Ethnic differences in primary angle-closure glaucoma. Curr Opin Ophthalmol 2006;17:175-80.
• Burr JM et al. The clinical effectiveness and cost-effectiveness of screening for open angle glaucoma: a systematic review and economic evaluation. Health Technol Assess 2007;11:1-190.
• Papadopoulos M, Khaw PT. Advances in the management of paediatric glaucoma. Eye 2007;21:1319–25.