INTRODUCTION

The benefits of healthy eyesight are enjoyed by most people in the developed world. However, the impact on eye health of the ageing process and modern lifestyles present many challenges to all those involved both in research and the delivery of eye care. In the developing world, the problems of meeting the urgent need to improve eye health are massive and sadly still not always being met.

Conditions presented in UK ophthalmology depart-ments and in general practice range from conjunctivitis (which has a variety of causes), eye trauma and tear deficiency to sight-threatening glaucoma, cataract and degenerative eye diseases. Some of these conditions are amenable to topical or systemic medication and/or surgery. The treatment of chronic degenerative eye conditions presents special problems.

Although the eye has built-in protective mechanisms, great care is needed to avoid microbial contamination and to maintain the stability and potency of topical eye preparations both in use and in storage. It is imperative to avoid cross-infection in all settings in which eye care is provided. The need to reduce the risk of infection when an eye injury is being investigated is critical, as it is in surgery.

Cataracts are a common cause of loss of useful sight in older people. Surgical procedures are widely and successfully carried out to correct this condition. Although no pharmacological treatment is available for cataracts, topical pre- and postoperative medication play a vital part.

There is a need to be aware that eyes can be signifi-cantly damaged or irritation caused by systemic drug treatment given for unrelated conditions, by improper care of contact lenses and by excipients such as preservatives contained in eye drops.

Many patients will need topical medication in the longer term. Such patients should be given support and guidance in using eye drops safely and effectively. Compliance aids can bring significant benefit to patients in the community, saving nursing time and achieving a better outcome for patients (see p. 469).

For some serious eye conditions (which may be hereditary), treatment options are limited. In particular, age-related macular degeneration can be treated with photodynamic therapy. As with all eye conditions, the aim is to minimise loss of useful vision and to protect or improve the vision the patient currently enjoys using all possible means.

As people are increasingly being encouraged to be more proactive in managing their own health, the need to value and protect healthy eyes cannot be overstated. A diet rich in antioxidants, regular eye checks and the use of eye protection will greatly benefit the individual and the NHS.

Nurses are increasingly carrying out ophthalmology procedures exclusively performed in the past by an ophthalmologist. Routine testing prior to examination by an ophthalmologist is part of the role of the nurse working in the outpatient department. Pre- and postcataract removal assessment, preparation and aftercare are the responsibility of nurses specialising in ophthalmic nursing. Eye care in general will continue to be an essential component of the total care of those unable to do this for themselves. A clear understanding of the subject is therefore of relevance to those working in any branch of nursing, be it in the patient’s home or in hospital.

ANATOMY AND PHYSIOLOGY

The eye is a spherical organ situated in the orbital cavity, whose bony walls and fat help to protect it from damage. The visible part of the eye is only a proportion of the whole, so that the eye is best con-sidered in vertical cross-section viewed from the side (see Fig. 23.1).

Fig. 23.1 The eye.

(From Page CP, Hoffman BF, Curtis M et al. 2006 Integrated pharmacology. Mosby, Edinburgh. With permission of Mosby.)

The walls are in three layers. The outermost layer is a fibrous coat consisting of the sclera (the white of the eye) covering all but the anterior part of the eye, which is transparent and known as the cornea.

In the middle is a vascular layer that, like the sclera, covers the posterior five-sixths of the eye and is known as the choroid. The anterior sixth comprises the ciliary body, an essential part of the process of accommodation of the eye, and the iris, the pigmented muscular structure that gives the eye its colour and serves, through autonomic nervous stimulation, to control the amount of light entering the eye.

In the centre of the eye is the eyeball, which consists of an anterior and a posterior segment separated by the lens. The anterior segment is in turn made up of an anterior chamber and a posterior chamber separated by the iris. Both chambers contain a transparent fluid, known as aqueous humour, secreted by the ciliary glands. Aqueous humour circulates from the posterior chamber through the pupil into the anterior chamber and back to the general circulation via the trabecular meshwork and then the canal of Schlemm. In health, the intraocular pressure (IOP) of fluid remains fairly constant. The remaining larger posterior segment of the eyeball is known as the vitreous body and is filled with a transparent, jelly-like substance that, along with the aqueous fluid, helps keep the shape of the eye.

The eye is protected by accessory organs, which include the eyebrows, eyelids and eyelashes and the lacrimal apparatus.

The lacrimal apparatus (see Fig. 23.2) is essential for the flow of tears. Tears are composed of water, salts and a bactericidal enzyme, lysozyme. Added to this fluid are oily secretions from the meibomian glands. These combined fluids serve to protect the eye in several ways:

Fig. 23.2 The lacrimal apparatus.

(From Waugh A, Grant A 2001 Ross and Wilson anatomy and physiology in health and illness, 9th edn. Churchill Livingstone, Edinburgh. With permission of Elsevier.)

The tear film has remarkable properties; flower-like crystal patterns up to 50 millionths of a metre across are thought to provide protection to the eye when we blink (Petrov 2006).

COMMON EYE CONDITIONS

EYE INJURIES

Eye injuries can result from a number of causes, notably foreign bodies, blunt injury or chemical damage. Injuries arising from the use of metal tools on wood, glass, stone or metal can result in penetrating injuries to the eye. Chemical damage to the eye must be treated with copious amounts of a suitable irrigating fluid (Dunne et al. 1991) such as sterile sodium chloride 0.9% solution or sterile water. In emergency situations, freshly drawn tap water may have to be used. Eye injuries due to chemicals of alkaline reaction, such as lime, need to be treated very urgently, because alkalis have a penetrating action on ocular tissue, causing iritis and cataract formation.

PRE- AND POSTOPERATIVE TREATMENT

Local eye treatment, both pre- and postsurgery, will depend on the condition being treated and the surgical procedures used. The main agents used are summarised in Table 23.1. Single-use containers must be used to reduce the likelihood of infection. If these are not available, a container should be reserved for the specific use of a named patient. It should be noted that many eye drop formulations contain preservatives and other adjuncts. These may cause sensitivity reactions.

Table 23.1 Drugs used in association with ophthalmic surgery

MEDICAL CONDITIONS AND THE EYE

Many serious medical conditions have ocular symp-toms. Examination of the eye may lead to the diagnosis of a serious general condition (e.g. diabetes mellitus, rheumatoid disease or hypertension). Systemic treat-ment is indicated in these conditions, the details of which are given in relevant chapters.

GLAUCOMA

Glaucoma is the commonest cause of blindness in the world. It is characterised by a raised IOP, which leads to cupping and degeneration of the optic disc, impairment of optic nerve head function and nerve fibre-type visual field loss. If the condition is untreated, defects in the field of vision enlarge, leading to visual loss. Normal IOP is 16 ± 3 mmHg. A pressure of 21 mmHg (measured by tonometer) or higher may represent a pathological condition and requires treatment. High IOP causes compression of the microcirculation of the optic disc, resulting in ischaemia, the extent of which will depend on the IOP and vascularity/blood supply of the optic disc. Some eyes can withstand an IOP of 30 mmHg or more without damage, owing to the presence of a good blood supply to the optic disc. In other eyes, a pressure of less than 21 mmHg can cause visual impairment. IOP is maintained as a result of balance between inflow and outflow of aqueous humour, which is secreted constantly by the ciliary body. The aqueous humour circulates around the lens before passing through the pupil into the anterior chamber. Aqueous humour leaves the eye through the angle of this chamber by filtering through the trabecular meshwork, and is returned to the general circulation via the canal of Schlemm. In addition to raised IOP, other risk factors for developing glaucoma include age, race and family history. These factors must all be taken into account when diagnosing the condition.

An increased IOP can result from an increased production of aqueous humour or from impaired drainage (Fig. 23.3). In clinical practice, most cases of glaucoma arise from poor drainage of the aqueous humour from the anterior chamber. This is believed to result from a progressive degenerative process in the trabecular meshwork and the endothelium of the canal of Schlemm.

Fig. 23.3 The anterior chamber of the eye, showing the normal pathway for secretion and drainage of the aqueous humour and blocking of circulation.

TYPES OF GLAUCOMA

Glaucomas can be divided into two main categories, namely primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).

PRIMARY OPEN-ANGLE GLAUCOMA

This is the most common form. Patients may not notice the gradual visual loss taking place, presenting only when serious damage has occurred. Hereditary factors are involved, and diabetics and very short-sighted people are especially at risk of developing this condition. Prevalence increases in the over-80 age group to 10%. Screening is advisable in certain situations (e.g. in older people and children of affected patients). Treatment of POAG is summarised in Tables 23.2–23.4. Latanoprost (and other prostaglandin analogues) is used to treat POAG as a once-daily eye drop. This costly product is reserved for use in patients in whom first-line treatments are inappropriate. The drug acts by increasing uveoscleral outflow. Patients should be monitored for changes in eye pigmentation.

Table 23.2 Treatment of primary open-angle glaucoma with beta-blockers

Table 23.3 Treatment of primary open-angle glaucoma with parasympathomimetics and sympathomimetics

Table 23.4 Treatment of glaucomas with carbonic anhydrase inhibitors

Brimonidine, a selective second-generation α₂-adrenoceptor agonist, reduces IOP by reducing aqueous humour production and enhancing uveoscleral outflow. Because this drug has no clinically significant effect on the heart or lungs, it may be a suitable alternative to beta blockers.

Carbonic anhydrase inhibitors act on the form of the enzyme found in the ciliary epithelium, reducing the production of aqueous humour.

PRIMARY ANGLE-CLOSURE GLAUCOMA

In this condition, the affected eye is hard, red and painful and the presentation is acute. The distinction between open-angle glaucoma and closure-angle glaucoma is made on the basis of the appearance of the anterior chamber angle on ocular examination. In this form of glaucoma, drainage of the aqueous humour is blocked by the iris. IOP builds up very quickly, vision becomes blurred and there is headache, sickness and ocular pain. Older and long-sighted people are more at risk than younger people of developing this condition.

Primary open-angle glaucoma and PACG are separate entities that require different management. PACG requires urgent intervention. Initially, IOP is reduced medically, followed by surgery to prevent recurrence. In both cases, the aim of treatment is to reduce IOP and maintain the reduction. Common glaucomatous conditions are compared and summarised in Table 23.5.

Table 23.5 Primary glaucomas: a comparison

Primary open-angle glaucoma or chronic simple glaucoma (POAG)

Acute closed-angle glaucoma or primary angle-closure glaucoma (PACG)

• In this condition, the angle of the anterior chamber is open Only gold members can continue reading. Log In or Register to continue Share this: Click to share on Twitter (Opens in new window) Click to share on Facebook (Opens in new window) Related Related posts: The role of patients and carers in medicines management Drug treatment of malignant disease Drug treatment of respiratory disorders Drug treatment of infections Stay updated, free articles. Join our Telegram channel Join Tags: Pharmacology and Medicines Management for Nurses May 13, 2017 | Posted by admin in NURSING | Comments Off on Drug treatment of eye conditions Full access? Get Clinical Tree Get Clinical Tree app for offline access Get Clinical Tree app for offline access