Common Eye Diseases of the Elderly

Introduction

As our global population ages, vision loss has become an increasingly important healthcare issue. It is estimated that approximately one in three adults aged over 65 will suffer from one form of vision-reducing eye disease. The most common causes of loss of visual acuity among the elderly population are cataracts, glaucoma, diabetic retinopathy and age-related macular degeneration (AMD). It is important to screen for these diseases early as they may initially be asymptomatic until permanent damage is caused. Reducing risk factors, such as cigarette smoking and exposure to ultraviolet light rays, may further minimise the disease burden.

Table 1. Presenting symptoms of common eye diseases of the elderly

Cataracts

Cataracts are defined as lens clouding and are the leading cause of blindness worldwide. The World Health Organization estimates that cataracts are responsible for 51% of all blindness, affecting approximately 20 million people in 2010. The majority of cases are due to the ageing process, however cataracts may develop as a result of trauma to the eye, inflammation of the eye, medications, or a genetic predisposition.

There are three common types of cataracts:

1. Nuclear cataracts are caused by a hardening and yellowing of the lens and tend to impair distance vision over near vision.
2. Cortical cataracts begin as wedge-shaped peripheral lens opacities. The first symptoms are often glare from focal light sources, such as headlights of oncoming cars.
3. Posterior subcapsular cataracts are more common in younger patient populations. Near visual acuity is affected to a greater capacity than distance visual acuity.

Treatment of cataracts includes surgical removal of the clouded lens and implantation of an artificial intraocular lens. This is usually performed under local anaesthesia in day surgery and results in immediate visual recovery. There is some controversy about whether surgery can quicken the onset of other age-related diseases such as glaucoma, diabetic retinopathy and AMD. For this reason, surgery is often withheld until reduced visual acuity interferes with the patient’s quality of life and daily activities.

Studies have shown that reduction of cigarette smoking and ultraviolet light exposure may prevent or delay the development of cataract. Diabetes mellitus and high body mass index are acknowledged as added risk factors in developing cataracts.

Glaucoma

Glaucoma is a group of optic neuropathies characterised by optic disc changes and irreversible and gradual visual field loss. Glaucoma is estimated to cause approximately 12% of global blindness, equating to 4.5 million people. The two most common forms of glaucoma are primary open angle glaucoma (POAG) and angle closure glaucoma (ACG).

An increase in intraocular pressure (IOP) is the only modifiable risk factor for glaucoma. It is important that treatment is initiated early to preserve visual field acuity and reduce the rate of progression, regardless of whether IOP is augmented or not.

POAG tends to have a slow and insidious onset. Topical medicines are first line therapy, either alone or in combination. These agents reduce IOP by decreasing aqueous humour production and/or increasing its outflow. It is important to monitor changes in visual field and optic disc appearance to determine the clinical effect of treatment. If topical agents are unsuccessful, surgical intervention by laser or incisional techniques may be warranted.

ACG is less common, but generally more acute. IOP tends to rise very quickly, so treatment should be initiated without delay. This condition may be treated with iridotomy (laser or surgical). This procedure creates a hole in the iris to allow the aqueous humour to flow between the anterior and the posterior chamber. There is little known about primary prevention of glaucoma, however medications and surgery are effective treatments if the disease is diagnosed early.

Age-related macular degeneration

Age-related macular degeneration (AMD) most commonly affects people over 50 years of age, causing loss of the central field of vision. Worldwide, AMD is the third most common cause of blindness after cataract and glaucoma, although it is the primary cause in industrialised nations. It is thought to develop due to circulatory insufficiency which then reduces blood flow to the macular area, resulting in degenerative lesions.

There are two different types of AMD:

1. Non-exudative (dry). This is the most common form, representing 90% of AMD cases. This condition typically causes gradual mild to moderate visual impairment over several months to years.
2. Exudative (wet). Wet AMD only accounts for 10% of cases, however it is responsible for 90% of the severe visual loss associated with AMD. This condition occurs due to haemorrhagic vessels blurring central vision. Laser photocoagulation may be used to reduce the risk of severe loss of vision and limit the extent of damage caused by exudative AMD, however there is no true cure for the disease.

Studies have shown that cigarette smokers are twice as likely to develop AMD as non-smokers, hence the need for smoking cessation in these patients. Diets high in carotinoids, antioxidants found in brightly coloured vegetables and fruits, may lower the risk of developing exudative AMD. The intake of antioxidant and mineral supplements for AMD prevention or treatment, however, remains controversial. Patients should be reassured that whilst AMD may result in a gradual loss of central vision, it almost never leads to complete blindness as peripheral vision remains unaffected.

Diabetic retinopathy

Diabetic retinopathy can occur in patients with type 1 or type 2 diabetes. Hypertension and chronically elevated blood glucose levels have been associated with microvascular damage which can lead to diabetic retinopathy. Diabetic retinopathy accounts for approximately 5% of world blindness. The condition usually presents in individuals living with diabetes for several years.

Diabetic retinopathy may be divided into two categories:

1. Nonproliferative diabetic retinopathy is characterised by abnormalities of the retinal circulation, macular oedema being the most common. This condition may be asymptomatic or cause blurred or distorted central vision.
2. Proliferative diabetic retinopathy occurs where newly formed blood vessels multiply from the optic disc, retina, or iris following widespread retinal ischemia.

Good glycaemic control is important as it decreases the risk of developing retinopathy and may slow its progression. Laser surgery is a viable treatment option for both forms of diabetic retinopathy. Best results are achieved when treatment is initiated early, emphasising the importance of adequate screening. Patients with both type 1 and type 2 diabetes mellitus should be screened when newly diagnosed, and every two years afterwards. Referral to an ophthalmologist and annual screening should occur if retinopathy is identified.

Conclusion

These four common eye diseases of the ageing population remain an ongoing healthcare challenge. Identifiable risk factors should be modified, where possible, to reduce disease burden. Due to the insidious nature of many of these conditions, early detection and initiation of treatment is essential in order to optimise patient outcomes.