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An overview of glaucoma and its management

Freda Sii
MB BS
Senior Educational Fellow, Moorfields Eye Hospital NHS Foundation Trust
Senior Glaucoma Fellow, University Hospitals Birmingham NHS Foundation Trust

Peter Shah
BSc(Hons) MB ChB FRCOphth FRCP Edin
Director of 'Eyes and Vision' Education, National Institute for Health Biomedical Research Centre for Ophthalmology and Moorfields Eye Hospital

Peng T Khaw
PhD FRCS FRCP FRCOphth FRCPath CBiol FSB FMedSci
Programme Director, UCL Partners Academic Health Science Centre
Director, Moorfields Eye Hospital and UCL Institute of Ophthalmology
Professor of Glaucoma and Ocular Healing and Consultant Ophthalmic Surgeon

Glaucoma is a group of conditions characterised by optic nerve damage and visual field loss. Good diagnosis and management prevents blindness, can be complex and requires a multidisciplinary approach

Glaucoma is the world's leading cause of irreversible but preventable blindness. The World Health Organisation (WHO) estimated that there were 4.4 million people who were blind from glaucoma in 2002.1 Approximately 10% of UK blindness registrations are due to glaucoma. The term 'glaucoma' is used to describe a heterogenous group of diseases in which the final pathway is damage to the optic nerve associated with visual field loss. The level of pressure in the eye (intraocular pressure, IOP) is the major modifiable risk factor in glaucoma.

Types of glaucoma
There are many different types of glaucoma but they are usually grouped into open angle glaucomas (OAG) and angle-closure glaucomas (ACG). In OAGs, the drainage angle appears morphologically normal, whereas in ACGs, the drainage angle is blocked by the iris.

Primary open angle glaucoma (POAG) is the main type of glaucoma in Caucasian populations. In the UK it affects about 1-2% of people over the age of 40, rising to 10% in people over 75 years of age. About half of all glaucoma cases in the community remain undiagnosed. The highest prevalence of POAG is found in people of African or African-Caribbean descent. It is approximately four times more common in this ethnic group, with patients presenting at a younger age with more aggressive disease.2-4 Risk factors for POAG are listed in Box 1.

[[Box 1,2 glaucoma]]

Normal tension glaucoma (NTG) is the term used to describe OAG when the IOP is consistently within the normal range (pressure at night (nocturnal hypotension), which may be caused by over-treatment of systemic hypertension, and obstructive sleep apnoea may be contributory risk factors in NTG.

Primary angle-closure glaucoma (PACG) can cause blindness rapidly. It accounts for half of all glaucoma blindness, and is much more prevalent in the East Asian populations.5 In the Caucasian populations, those eyes that are hypermetropic (long-sighted) and small in size are most at risk. There is an acute form of PACG, sometimes called 'acute glaucoma' (for symptoms, see Box 2), in which there is a rapid rise in IOP to very high levels (up to 70 mmHg). This is an ophthalmic emergency.

Secondary glaucomas are less common, but the risk of blindness is greater than POAG as the level of IOP can be very high. In severe diabetic eye disease, neovascularisation (growth of abnormal blood vessels) causes damage to the trabecular meshwork, which can result in severe IOP elevation (neovascular glaucoma).

Congenital glaucoma manifests very early in life, usually within the first year of life and is due to abnormal development of the outflow channels. Children may also develop secondary glaucoma, for example in association with cataracts and cataract surgery or inflammation.

Glaucoma and diabetes
There has been conflicting evidence on the link between diabetes mellitus and glaucoma. Most researchers now believe that there is a mildly increased risk of developing glaucoma in diabetes and the current recommendation is that diabetics should be screened for glaucoma on an annual basis.
The management of neovascular glaucoma is extremely difficult, and every effort should be made to prevent severe diabetic eye disease. The primary care team are optimally placed to educate patients and help them to optimise their glycaemic control. It is also important to control associated risk factors for severe diabetic eye disease, including hypertension, serum lipids and renal disease.

Symptoms and signs
Patients with POAG are generally asymptomatic until late in the disease course, as it affects the peripheral visual field first. It is a silent disease and is often called 'the thief of sight'. However, there may be subtle symptoms, such as missing steps and tripping over when the lower half of the visual field is affected. To the casual observer, the eye looks normal. The
symptoms are much more dramatic in high IOP acute glaucoma. These patients are very distressed because of severe eye pain. Some also experience nausea and vomiting, and can be occasionally misdiagnosed with an abdominal problem. The vision is blurred. The eye is red with a cloudy cornea and the pupil becomes fixed and mid-dilate.

Other patients with chronic PACG may only experience intermittent angle-closure with milder symptoms, such as halos around lights at night and mild ocular pain or headache, especially after reading for an extended period. Some of these patients may later progress to acute glaucoma. Children with congenital glaucoma usually present in their first year of life with large eyes and are often photophobic with watery eyes. They may have cloudy corneas from corneal oedema.

Diagnosis
The diagnosis of glaucoma is usually made by an ophthalmologist (eye surgeon). Glaucoma screening is usually performed by optometrists in the community and glaucoma suspects are then referred to the hospital eye service. Full glaucoma assessment involves the following:

  • History.
  • Visual acuity.
  • Full slit lamp examination, which includes:
    - Tonometry (IOP measurement).
    - Gonioscopy to assess the drainage angles.
    - Ophthalmoscopy to assess the optic discs for
    glaucomatous damage.
  • Visual field testing.
  • Optic disc imaging.

Management
The main aim of glaucoma treatment is to halt the progression of glaucomatous damage and visual field loss. IOP reduction is the mainstay of glaucoma management. This can be achieved by reducing aqueous production or increasing aqueous outflow or both, by means of medical, laser or surgical treatment. If there is an underlying condition or a contributory factor, this also needs to be addressed, eg, in NTG and secondary glaucoma.

The initial management of raised IOP is to medically reduce the IOP with glaucoma drops. It is important to realise that a small amount of the drug instilled onto the eye is absorbed systemically and patients can have sight- or life-threatening complications. Some of the systemic side-effects of β-blockers can be minimised by correct instillation of drops and using punctal occlusion or eye closure to stop the drug from draining into the nasal passages and being absorbed systemically via the nasal mucosa.

It is not uncommon to develop an allergy to one or more of these glaucoma drops over time. This may occur soon after initiating the treatment, but can also happen many years later.
The allergic reaction may be to the drug itself or to the preservative agent (eg, benzalkonium chloride). The eye becomes red and sore, the eyelids become red and swollen, and the skin around the eye looks eczematous. The eye is not always itchy. If this is associated with the introduction of a new drug then this should be stopped. If the patient is on multiple drops and develops an allergy it can be difficult to isolate the offending agent. Sometimes, all drops may need to be stopped and oral acetazolamide used to control IOP while the allergic reaction resolves, usually within a few weeks. Preservative-free glaucoma drops are available for patients allergic to the preservative agents.

Another potential reaction to the drops is toxicity to the eye surface. Patients on long-term multiple drops are more at risk. The eyes become red and sore and the patient finds it increasingly difficult to tolerate the drops. Dry eyes can exacerbate the symptoms. Ocular toxicity due to drops can be managed by lubrication with artificial tears and the use of preservative-free glaucoma drops. Preservative load to the ocular surface can also be minimised by using combination drugs (eg, a prostaglandin analogue combined with a β-blocker in a single bottle). Combination drugs also simplify the drop regimen, which is particularly useful in elderly patients who sometimes have difficulty coping with complex drug regimens.

Acute glaucoma must be referred urgently to an eye casualty. IOP reduction is achieved with medical treatment initially. Laser peripheral iridotomy (to create a small hole in the peripheral iris) is later performed to help open up the drainage angle. Other possible treatments include laser iridoplasty (lasering the iris surface to cause contraction and changing the iris configuration) and cataract surgery (to deepen the anterior chamber and drainage angle).

Trabeculectomy is the gold standard for glaucoma surgery and aims to produce a bypass valve to allow aqueous leave the eye. In modern trabeculectomy, tiny local doses of anti-cancer agents (eg, 5-fluorouracil or mitomycin C) applied by sponge or injection in conjunction with topical steroids are used to minimise the scarring process after surgery and, therefore, increase the success rates. In severe glaucoma which is refractory to other modalities drainage devices can be implanted into the eye.

Challenges in glaucoma management
Management of glaucoma, a lifelong disease, can be very challenging. A significant proportion of patients become intolerant to treatment (developing allergy to the drugs or the preservatives, ocular toxicity, or significant systemic side-effects).

In some patients with secondary glaucoma, IOP elevation remains refractory despite maximally tolerated medical therapy, including oral acetazolamide. Surgery may be the only option for these patients, but it can pose both technical and anaesthetic problems in an increasingly elderly population.

Non-adherence is a major problem in glaucoma management as many patients are relatively asymptomatic until they have significant loss of vision. Persistently raised IOP due to non-adherence is often misdiagnosed as treatment failure, resulting in an increase in medical therapy or in surgery unnecessarily.

It is important that patients bring their glaucoma medications to all appointments. This will help identify problems such as using expired eye drops, confusion with multiple drop regimens or poor instillation technique, all of which reduce treatment efficacy. Older patients with reduced dexterity have the additional problem of difficulty in handling small bottles and instilling drops accurately. Some hospitals have nurse advisors to educate patients about glaucoma, including how to instill eyedrops.

There are various drop-aids available for older patients or individuals with arthritis. Sometimes family members can be very helpful. However, a proportion of older patients live on their own and may benefit from the help of district nurses with their drop regimenand instillation. Glaucoma support teams (usually comprising glaucoma specialist nurses) aim to work with patients to optimise their glaucoma care. A trained primary care team (GP and primary care nurses) can potentially play an important supporting role in patients' glaucoma care. This can be achieved by providing patient education, improving patient adherence, optimising drop instillation techniques, detection of problems (allergic reaction, side-effects and postoperative infection) and minimising the rate of patient non-attendance/loss of follow-up.

Conclusion
Glaucoma is a complex group of diseases and management requires a multidisciplinary approach. Ophthalmologists, glaucoma support teams and patients are on a journey together to prevent glaucoma blindness. The involvement of well-trained primary care teams in this challenging journey will greatly help patients and reduce avoidable glaucoma blindness.

References

  1. Resnikoff S, Pascolini D, Etya'ale D et al. Global data on visual impairment in the year 2002. Bull World Health Organ 2004:82:844-51.
  2. Wormald RP, Basauri E, Wright LA, Evans JR. The African Caribbean Eye Survey: risk factors for glaucoma in a sample of African Caribbean people living in London. Eye 1994;8:315-20.
  3. Tielsch JM, Sommer A, Katz J, Royall RM, Quigley HA, Javitt J. Racial variations in the prevalence of primary open-angle glaucoma. The Baltimore Eye Survey. JAMA 1991;266:369-74.
  4. Leske MC, Connell AM, Schahat AP, Hyman L. The Barbados Eye Study. Prevalence of open angle glaucoma. Arch Ophthalmol 1994;112(6):821-9.
  5. Foster PJ, Baasanhu J, Alsbirk PH, Munkhbayar D, Uranchimeg D, Johnson GJ. Glaucoma in Mongolia. A population-based survey in Hovsgol province, northern Mongolia. Arch Ophthalmol 1996;114:1235-41.