Ординатура / Офтальмология / Английские материалы / Ophthalmic Drugs Diagnostic and Therapeutic Uses 5th edition_Hopkins, Pearson_2007

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Chapter 17

Ocular first aid

FIRST AID

From time to time, optometrists will be confronted by a variety of emergency situations, both ocular and general. The term ‘first aid’ is very apt and it is important that procedures are kept simple and to a minimum. It is worth stating the underlying principles of first aid that should govern the optometrist’s action in an emergency situation:

•Separate the patient from the cause of the trauma: if there is an external cause, this should whenever possible be removed from the patient (e.g. a foreign body) or the patient from it. The important words are ‘whenever possible’, as there are situations in which this aim cannot be achieved or to do so would exacerbate the patient’s condition. For example, intraocular and embedded foreign bodies should be left for ophthalmological removal. On the other hand, superficial foreign bodies should be removed if possible and the elimination of chemical splashes on the eye must not be delayed, as in both cases damage will continue to develop while they are in contact with the eye.

•Relieve distress and make the patient as comfortable as possible: much of this can be achieved by reassurance from the optometrist. In many simple emergency cases, patients will believe that they are more injured than they really are, so a confident approach will do much to dispel these fears. The commendable desire to relieve the patient’s symptoms should not, however, lead to indiscriminate use of local anaesthetics.

•Seek medical assistance as soon as possible: the implementation of first aid procedures should not delay the patient’s referral for medical assistance.

Of course, optometrist will be confronted by general emergencies as well as ocular ones. Patients are not immune from such conditions such as epistaxis (nosebleed), syncope (fainting) and heart attacks. A short course in general first aid techniques would thus be useful for all optometrists. This chapter covers only ocular emergencies.

Whatever the emergency, traumatic or medical, serious or trivial, proper records must be kept of each case encountered. These should include the following details:

•Name and address of patient requesting attention.

•Date of treatment.

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•local anaesthetics, e.g. benoxinate, amethocaine

•fluorescein in some form, e.g. single-use eyedrops or paper strips

•antibacterial agents, e.g. chloramphenicol, framycetin

•emollient drops, e.g. castor oil, liquid paraffin

•normal saline for irrigation.

In most cases where irrigation is required, running water is probably the best medium as it is unlikely that sufficient volume of normal saline will be stocked.

Specific antidotes to cope with chemical injuries to the eye are not worth keeping, as dilution by irrigation is probably the best method.

COMMON OCULAR EMERGENCIES

The common ocular emergencies are:

•superficial foreign body

•intraocular foreign body

•blow with a blunt instrument

•chemical burns

•thermal burns

•exposure keratitis

•acute closed-angle glaucoma.

SUPERFICIAL FOREIGN BODY

This is the most common ocular emergency to be encountered and the stages of dealing with it are as follows:

•history

•local anaesthetic (if necessary)

•location

•removal

•staining

•visual acuity assessment

•prophylaxis

•records

•corneal sensitivity.

History It is very important to ascertain the circumstances in which the foreign body came in contact with the eye because in every case of superficial foreign body there is always a possibility of an intraocular foreign body and the latter must be positively discounted rather than assumed to be absent. Foreign bodies that result from any kind of explosion, however mild, or are thrown up by moving machinery, can sometimes penetrate the eye rather than remaining on the surface.

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Local anaesthetic Foreign bodies cause discomfort and this in turn leads to reflex tearing and blepharospasm. The optometrist is thus confronted by an eye that is closed and difficult to open. Under these circumstances, a local anaesthetic can be used to facilitate examination and to alleviate the patient’s discomfort. Any of the usual topical anaesthetics are suitable: tetracaine, benoxinate, proxymetacaine or lidocaine.

The use of a local anaesthetic is only justified prior to the removal of a foreign body. Problems can arise when local anaesthetics are used to relieve the discomfort that remains after the foreign body has been removed. Attention has been drawn to the dangers of the overuse of local anaesthetics in Chapter 9.

Location The foreign body should be located if possible. It is not unknown for the reflex tearing to dislodge the object and do the optometrist’s job. If the foreign body is not immediately visible on inspection it is probably trapped under the upper lid, necessitating eversion of the lid, or even double eversion, to locate it.

Removal Providing that it is not embedded, the object can be removed, either with a cotton bud or by irrigation with eye lotion or running water. If the particle is embedded, the patient should immediately be referred to the hospital accident and emergency department for medical treatment.

Staining After removal of the foreign body, staining with fluorescein should be carried out to assess the extent of any disturbance to the corneal epithelium. This information will enable the optometrist to decide whether to refer the patient to his general practitioner or whether to ask the patient to return on a subsequent visit for re-examination.

Records As stated above, full and accurate records are essential and the point is reinforced here because it might be thought that a trivial event, such as a foreign body that is easily removed, does not warrant the writing up of records. However, it is just this kind of case that could lead to problems

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in the future if full details of the history, drugs used, procedures carried out and the results of visual acuity measurement and corneal examination cannot be recalled.

Corneal sensitivity If a local anaesthetic has been used, it is important to check that sensitivity has returned to the eye. It would be ironic – to say the least – if the patient, having had a foreign body removed, were sent out onto the street in a condition in which he or she would be unaware of the entry of another one.

INTRAOCULAR FOREIGN BODY

Whereas a superficial foreign body might be considered as a relatively trivial problem, an intraocular foreign body is a very serious event that always requires medical attention. Admittedly, the eye will tolerate pieces of glass and plastic (e.g. intraocular lenses) relatively well compared with metals such as copper or iron or organic materials (vegetable or animal), but there is always the threat of infection either from the foreign body itself or from opportunistic organisms gaining access through the entry wound.

There is little an optometrist can do for a patient with an intraocular foreign body other than to refer the patient for medical treatment. The optometrist’s great service to the patient is in the discovery of such an invasion in doubtful cases. The foreign body might be visible by ophthalmoscopic examination or the entry wound might be visible as a rivulet of aqueous. However, the entry wound might not be visible and the only indication of an intraocular foreign body will be the history. Any suspect case must be referred.

BLOW WITH A BLUNT INSTRUMENT

Although the bony orbit provides a good protection against damage, sometime objects (e.g. squash balls) can penetrate this protection and impact on the eye. Even larger objects can exert such a force to the surrounding tissue as to cause fractures and ocular damage.

The result of a blow can be alarming, with marked swelling and bruising. These will normally resolve spontaneously but there are serious sequelae to blows:

•detached retina

•cataract or lens subluxation

•commotio retinae

•traumatic macular degeneration

•blow-out fracture

•iris damage (iridodialysis)

•haemorrhage.

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The patient experiences intense pain, which might be severe enough to induce vomiting. The conjunctival blood vessels are dilated, giving the appearance – to the inexperienced observer – of conjunctivitis. The cornea loses transparency slightly because the high intraocular pressure causes it to imbibe water and swell, which the patient might report as seeing haloes around lights. Through the hazy cornea the pupil can be seen, often mid-dilated (Chandler 1952) and probably non-circular. The pupil will not constrict to light, accommodation or to the action of miotics. The intraocular pressure, whether measured with a tonometer or assessed digitally, is very high. The situation is an emergency one, but not requiring panic measures. Providing the intraocular pressure is reduced over the ensuing few hours, there should be no long lasting damage.

Although the iris will not react to miotics because of ischaemia, one should still be administered. When the pressure is reduced by systemic methods, the miotic will be present in the aqueous ready to exert its action. A drop of 2% pilocarpine eyedrops should be given to both eyes and repeated at 10-min intervals (Norden 1978).

Several first aid methods can be tried to reduce the pressure systemically and the decision to use one of these will depend on the proximity and availability of expert medical help. The use of glycerol (glycerine) has been recommended as an osmotic agent that can be given orally in orange juice to reduce the intraocular pressure sufficiently to allow the miotic to act. About 250 mL of glycerol has been suggested as the amount required for a 70-kg adult (Norden 1978). However, this might not be acceptable to the patient and 100 mL might be more appropriate. It is advisable to omit this part of the treatment if the patient has diabetes. In any case, the patient should be referred as soon as possible to an accident and emergency department.

References

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SECTION I V

Adverse effects

Chapter 18

Drug interactions

A change in the efficacy or toxicity of a drug in the presence of another drug, food, drink or other chemical is called a drug interaction. Sometimes the interaction leads to excessive therapeutic effect, which exceeds the required clinical effect and leads to overdose symptoms. In other cases, the therapeutic effect is reduced, leading to undertreatment. However, not all interactions are harmful and drugs are given in combination expressly because they interact or have a synergistic effect. The term ‘interaction’ does not include direct in vitro reactions between drugs such as occurs between sodium fluorescein and benoxinate hydrochloride. These are called drug incompatibilities.

There are many different mechanisms by which drugs can interact with one another. They can interfere with the metabolism, absorption and excretion of the drug (pharmacokinetic interactions) or they can influence the pharmacological action (pharmacodynamic interactions). At present, not all mechanisms of interaction can occur with ophthalmic drugs but are included for completeness.

PHARMACOKINETIC INTERACTIONS

INTERACTIONS AFFECTING ABSORPTION

Many factors affect absorption and drug absorption can easily be influenced by changes. Drug absorption is dependent on the pH of the medium from which the drug is absorbed not only in the tear film in the conjunctival sac but also when drugs are absorbed from the gut. The dwell time of a drug in the eye will affect how much drug is absorbed and hence its depth and duration of effect. A reduced tear flow will increase the dwell time and hence a local anaesthetic instilled prior to another drug will enhance its effect. A reduction in corneal integrity will similarly increase absorption.

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INTERACTIONS AFFECTING PROTEIN BINDING

When some drugs are administered, a proportion becomes bound to plasma proteins and only the unbound proportion is available to react with receptors. Two drugs might combine with the same binding site on the protein molecule and compete with one another. Hence the presence of a second drug could reduce the number of sites and hence increase the activity of the first.

INTERACTIONS AFFECTING BIOTRANSFORMATION

A few drugs leave the body in the same chemical form as they entered it but the vast majority are modified in some way. Prodrugs have to be enzymatically activated to produce their effects but most biotransformations involve producing a less active, more easily excretable derivative of the original drug and are referred to as detoxifications. Interacting drugs might potentiate the action of detoxifying enzymes (enzyme inducers) and reduce their action (enzyme inhibitors). Enzyme inducers (which for some drugs includes tobacco smoke) will cause an increase in the rate of detoxification and hence a reduction in the action of the drug. Enzyme inhibitors will have the opposite effect. Chloramphenicol affects the serum levels of phenytoin, an antiepileptic drug when given systemically. It is unlikely that sufficient of the antibiotic will be absorbed when given as eyedrops. One important enzyme inhibition is the interaction of erythromycin and certain antifungals with the commonly used antihistamine terfenadine. This results in cardiac arrhythmias in susceptible patients.

INTERACTIONS INVOLVING EXCRETION

These interactions usually involve the kidney and are caused by changes in the blood flow through the kidney or changes in pH.

PHARMACODYNAMIC INTERACTIONS

ADDITIVE EFFECTS

Two drugs with similar actions can cause a variety of effects when given together. These effects can be additive, when the combined effect is the same as the combined effects of the two drugs given singly, potentiated, where the effect of one drug is increased, or synergistic, when the combined effect is greater than that of the drugs on their own. When the two drugs act on the same receptor, unpredictable results can occur. For example, pilocarpine and physostigmine are not synergistic and might, in fact, be antagonistic. Similarly, reversible anticholinesterases will