Initial Assessment of the Eye

Eye problems account for approximately 6% of all attendances to an ED in the UK [1,2] with an incidence of 17.2 ophthalmological emergencies per 1000 population per year. Injuries account for nearly half of the total. [3]

Although around two thirds [2,4] of all eye problems are managed solely by the ED many trainees receive little or no training in ophthalmic emergencies in their post. [5]

This lack of knowledge is reflected by studies highlighting poor assessment and examination of patients with eye problems presenting to the ED. In one, a third of patients did not have their visual acuity tested [5] and in another, a fifth of histories and 59% of examinations were judged to be inadequate. [6]

Learning Bite

Although two thirds of all eye problems can be managed solely by the Emergency Physician, equipment and training are deficient and clinical assessment by junior doctors is poor.

No assessment of eye problems can be undertaken without a knowledge of the basic anatomy of the eye.

The majority of eye problems presenting to the ED relate to the anterior eye.

 

Common sites of injury and infection are:

• Cornea
• Conjunctiva
• Eyelids

Visual disturbance can arise as a result of a problem with any structure along the visual axis or neural visual pathway.

Any patient assessment in the ED must begin with an ABC assessment.

Between 40-60% of all eye problems are trauma related and, therefore, consideration must be given to:

• The rest of the face and head
• Airway
• Cervical spine
• Any other related injuries

History

An ophthalmological history covers not only presenting symptoms and previous eye problems, but must also consider whether an underlying systemic disorder is present.

Considering three common ED presentations:

1. Visual loss

Features of the history may be very useful in discriminating between different causes of visual loss.

Features	Causes
Does the disturbance affect one or both eyes?	Acute bilateral eye pathology is rare and often a hemianopia patient will complain of visual loss in one eye rather than both.
How quickly did the disturbance appear?	A rapid onset suggests a vascular problem or retinal detachment A slower onset suggests a more chronic process such as a space occupying lesion
Is the disturbance partial, or a complete loss of vision?	Complete loss of vision in one eye localises pathology to that eye or optic nerve, e.g. retinal artery or vein occlusion.
If the disturbance is partial, what form did it take?	Partial loss of vision must be differentiated between: A loss of part of the visual field, e.g. quadrantopia, hemianopia or central scotoma A curtain coming down across the vision a typical description of a retinal detachment Flashes usually due to retinal ischaemia Floaters due to opacities in the vitreous body, which may be normal, but a sudden increase may be found in vitreous haemorrhage and retinal detachment.

2. Red eye

Some important features to elicit from the history include:

• Contact with others with similar symptoms likely to be viral conjunctivitis
• Severe deep pain seen in acute glaucoma, anterior uveitis
• Contact lens wear corneal ulceration is more common
• Presence of systemic symptoms, e.g. joint pains suggests generalised inflammatory disorder

Although it is tempting to try and differentiate between viral and bacterial conjunctivitis based on the history alone, no reliably accurate method
exists. [7]

3. Trauma

It is important to attempt to differentiate blunt from high velocity or potentially penetrating trauma.

Significant blunt injury to the eye often occurs in association with:

• Assaults
• Sporting situations from direct impact by a ball

Activities associated with high velocity fragments hitting the eye include:

• Angle grinding
• Use of a metal chisel with a hammer

Visual Acuity

Visual acuity is a simple and useful measure of the ability of the eye to resolve fine detail. It is an essential component of the assessment of all patients presenting to the ED with an eye problem. Traditionally, it has been tested by asking the patient to read letters (known as optotypes) from a chart, commonly the Snellen chart. [8]

The chart is placed at a set distance, usually 6m, and each eye is tested individually by covering the other eye. [8]

The letters are sized according to distance, i.e. the largest letter, size 60, can be seen at 60m by a person with normal vision.

The acuity is recorded as a fraction, with the numerator as the distance from the patient to the chart, over the denominator as the lowest line that more than half the letters can be seen, e.g. 6 / 12 for a patient at 6m who is able to see the letters on the size 12 row. If the patient is unable to see some of the letters on a line, the acuity is recorded as:

A Snellen Chart

Although widely available in EDs, the Snellen chart method of acuity measurement is prone to error. One survey found that the chart distance and illumination varied enormously. [9]

Ensuring proper lighting for both the room and the Snellen chart is essential. The recommended chart luminance should be 80 to 320 cd/m². [8]

Also, technical problems occur due to the progressive increase in the number of letters down the chart. This leaves patients with poor acuity fewer letters to identify and a visual crowding of letters lower down the chart. [10]

These problems have been addressed by the development of newer charts, e.g. LogMAR, with identical numbers of letters on each line and greater accuracy of measurement. [11]

LogMAR chart

 

Learning bite

When measuring visual acuity it is vital that the chart is the correct distance away from the patient and independently illuminated.

Measurement Problems

A number of problems can arise when measuring visual acuity, such as:

• The patient has forgotten his/her glasses or has taken contact lenses out (What to do 1)
• The patient doesnt understand English or cant read (What to do 2)
• The patient is unable to see the top line of the chart (What to do 3)
• The patient cant open his/her eye due to photophobia or involuntary closing of the eyelid (blepharospasm) (What to do 4)

What to do 1

Use a pinhole occluder. The pinhole only allows parallel rays of light through, which pass straight through the cornea and lens without bending. Therefore, an unaltered image is presented to the retina. If acuity improves with the pinhole, the visual impairment is refractive and not due to an intrinsic eye or neurological disorder.

Learning bite

Use of a pinhole occluder corrects for any refractive error and enables a true visual acuity to be measured.

 

What to do 2

Alternative eye testing charts are available:

What to do 3

If acuity is so poor that the patient cannot see the top line of the chart, then assess at 3m, ensuring that this is documented as 3 / x.

If no letters are seen at the shorter distance, the next step is to assess ability to count fingers (recorded as CF).

If finger counting fails, then assess ability to perceive hand motion (HM).

Finally, if unsuccessful with the above, assess ability to perceive light (LP).

What to do 4

Instillation of local anaesthetic will often provide relief with an anterior eye problem, enabling the eye to be opened and acuity assessed.

Occasionally, treatment must precede visual acuity assessment, e.g. eye washout in chemical eye contamination.

 

External examination of the eye must include:

Start by examining the face for skin lesions and rashes, particularly if in a dermatomal distribution suggesting varicella zoster infection.

Lymphatic drainage of the eyelid and conjunctiva is to the pre-auricular and submandibular lymph nodes, which should be palpated for lymphadenopathy.

The temporal arteries should be felt for tenderness and the trigeminal and facial nerves examined for intact function.

A general external examination of the eye must include:

Orbit

The bony orbit and zygomatic complex should be palpated for swelling, tenderness, palpable fractures and subcutaneous emphysema.

Check for intact sensation in the supra- and infra-orbital nerve distributions (the forehead above the eye, and the cheek and upper gum, respectively).

These cutaneous nerves are particularly susceptible to injury from assault, as they emerge through foramina immediately above and below the eye.

Eyelids/globe position

Any generalised or local swelling should be identified.

Note the position and symmetry of the eyelids:

• Ptosis (e.g. third nerve palsy) or
• Retraction (e.g. exophthalmos)
• Entropion or ectropion

Any wounds must be examined carefully to identify depth and extension to the lid margin and possible involvement of the lacrimal apparatus.

The globe may appear to be:

• Protruding, e.g. retrobulbar haemorrhage or
• Sunken, e.g. Horners syndrome

Conjunctiva/cornea

An initial examination of the visible conjunctiva and cornea (palpebral fissure) should identify:

• General or localised swelling
• Colour
• Bleeding
• Clarity of the cornea

Note the distribution of any redness or prominent blood vessels of the conjunctiva (conjunctival injection):

• Generalised injection suggests conjunctivitis
• Localised injection is a sign of scleritis and episcleritis (image shows localised conjunctival injection in episcleritis)
• Perilimbal injection (surrounding the cornea, also known as ciliary flush) is seen in keratitis, acute glaucoma and other significant intraocular disorders

Pupil/iris

Examination of the pupil must include assessment of the size, symmetry and reflexes.

How is pupil size measured?

Although pupil size is often guessed, a ruler will provide a more accurate measure. If a ruler is unavailable, or in an emergency, either use a Haab scale or, remembering that a normal cornea measures 12 x 12mm, make a rough estimate of the proportion that the pupil takes up and, thereby, its size, e.g. 50% = 6mm.

How do you know if the pupil is dilated or constricted?

In a situation where a comparison cannot be made with the other eye or it is clinically important to judge if the pupils are dilated or constricted, the normal range for the size of pupils in different light conditions is often guessed. A study of pupillary size in bright (penlight or ophthalmoscope) and fluorescent light found that pupil sizes greater than 3.6mm or less than 1.9mm in bright light, or greater than 5mm or less than 2mm in fluorescent light, were likely to be abnormal. [12]

Learning Bite

a pupil smaller than 2mm or larger than 5mm measured in a room lit by fluorescent light, is likely to be pathological.

 

Symmetry

Other factors to take into account when measuring and comparing pupils are:

• Repeated pupil size measurements by the same or different observers

Research has found high levels of agreement between observers as long as formal measurement of papillary size was undertaken with a Haab scale. Simple estimation was associated with poor correlation. [13]

• Difference between pupil sizes

Anisocoria (unequal pupil sizes) is found in 19% of normal subjects at any one time and is more apparent in the dark than the light. [14] Unilateral miosis may be found in the acute red eye and is more prevalent with more serious problems (e.g. keratitis, uveitis). [15] The mechanism is thought to be due to release of prostaglandins into the eye which act on the sphincter pupillae. Other pathological causes of unequal pupils are shown in Table 1.

Previous surgery

Traumatic mydriasis from blunt eye trauma

Topical medication

Oculomotor nerve palsy (dilated pupil)

Holmes-Adie syndrome (dilated pupil)

Horners syndrome (constricted pupil)

Argyll Robertson pupil (constricted pupil)

Learning Bite

Approximately 20% of the normal population has unequal pupils. A smaller pupil is often found in the acute red eye.

 

How do I assess pupil reflexes?

A common method involves using a penlight to observe the pupils reaction to light and to see if the pupil constricts and dilates normally. The reaction of the pupil to both direct and indirect (consensual) bright light and accommodation should be assessed and recorded. [16]

A non-reactive or fixed pupil may indicate a neurological emergency. A pupil that is slow or fails to react to light, but reacts to accommodation, is commonly due to one or other of:

• Optic neuropathy
• Holmes-Adie syndrome
• Argyll-Robertson pupil

No reaction to light or accommodation is most likely due to either oculomotor nerve palsy, or the use of a mydriatic drug. [16]

A relative afferent pupillary defect (RAPD) (Marcus-Gunn pupil) indicates disease anterior to the optic chiasm, usually in the optic nerve or retina. It is identified by the swinging light test, conducted in a dimmed environment.

Normally, pupillary size is dependent on the total perceived light reaching the brain. If, when rapidly moving a bright light between the two eyes, one (abnormal) eye transmits less light to the brain, which reacts by dilating both pupils, as shown in the following links.

A normal reaction

Flash a bright light first into one eye for 2-3 seconds; both pupils should constrict. Then rapidly move to the other eye for a similar time. Normally, both pupils should remain constricted.

An abnormal reaction (RAPD in left eye)

If, once the light is moved from one side to the other, the pupils dilate, this is abnormal and represents a relative afferent pupillary defect in this case, pathology in the left eye, or optic nerve.

Learning Bite

A relative afferent pupillary defect indicates retinal or optic nerve pathology.

Eye movements

An examination of eye movements assesses normal function of the three cranial nerves and six muscles involved in eye movement.

If abnormal, it is important to consider both local and central problems, e.g.

• Orbital cellulitis
• Orbital blow-out fracture
• Swelling
• Cranial nerve palsy

Start by holding a pen torch approximately 30cm from the centre of the patients face and look for a symmetrical corneal light reflex, which indicates a central position of both eyes.

Trace either a rectangular box or an H figure, moving the patients eyes to each corner.

 

Abnormal Eye Movements

Here is a summary of the findings and causes of abnormal eye movements. In each image, the right eye is always the abnormal one.

III nerve (oculomotor) palsy

• Description: affected eye lies down and out with a dilated pupil
• Common causes: aneurysm, trauma, microvasculopathy, e.g. diabetes, atherosclerosis

IV nerve (trochlear) palsy

• Description: affected eye elevated on forward gaze, accentuated on head tilting to affected side
• Common causes: trauma, microvasculopathy

VI nerve (abducens) palsy

• Description: affected eye adducted at rest and no movement on lateral gaze
• Common causes: space occupying lesion, trauma, aneurysm

Internuclear ophthalmoplegia

• Description: one or both eyes fail to adduct
• Common cause: multiple sclerosis (lesion in medial longitudinal fasciculus)

 

Visual Fields

Visual field assessment is an essential component of the examination of any patient complaining of visual loss.

In the ED an estimation can be made using a confrontation technique. A white topped pin is more sensitive than a wiggling finger.

This visual field loss flowchart outlines the common field defects seen and their causes:

The following techniques and investigations are used in further assessment of the eye:

Fluorescein instillation

Fluorescein is an orange red dye that absorbs blue light and fluoresces green. It stains the tear film and only penetrates defects in the epithelium of the eye, making lesions such as corneal abrasions, foreign bodies and ulcers far more visible.

The most effective preparations for diagnostic purposes are either a 1% solution or a moistened floret. [17]

Contact lenses must be removed prior to instillation as they may become permanently stained.

Local anaesthetic instillation

Examination may be made easier in the painful eye if a topical local anaesthetic is instilled. Commonly used agents include:

• Tetracaine
• Lidocaine
• Proxymetacaine

Unfortunately, instillation of local anaesthetic drops into the eye is painful. Attempts to reduce pain by adding sodium bicarbonate to tetracaine increased pain scores. [18] Research has shown that proxymetacaine is the topical local anaesthetic of choice, as it produces the lowest pain scores with an equivalent clinical efficiency. [19]

Learning bite

Proxymetacaine is the least painful local anaesthetic agent when instilled into the eye.

Eyelid eversion

Eversion of the eyelid is a simple but essential investigation to look for foreign bodies and conjunctival inflammation.

This video link demonstrates the technique.

Fundoscopy

The skill of fundoscopy is a difficult one to master but an important part of the assessment of the eye.

This video link demonstrates the basic technique.

There is no doubt that fundoscopy is far easier if the pupil has been dilated the sensitivity of detecting diabetic retinopathy is twice as high through a dilated than a non-dilated pupil. [20] Tropicamide is a short acting mydriatic but there is a commonly quoted risk of precipitating acute glaucoma. A systematic review found this risk to be approximately 1:20,000. Even in several studies in high risk populations with chronic glaucoma, not a single patient developed acute glaucoma. [21]

Learning bite

Fundoscopy is more sensitive when the pupil is dilated and the risk of precipitating acute angle glaucoma with 0.5% tropicamide is extremely small.

It is important to make sure that patients who have driven to the ED are aware that their vision will remain blurred until the tropicamide wears off and that they make alternative arrangements for getting home.

Slit lamp

Of all the skills needed to assess the eye, use of the slit lamp is the most demanding. Familiarity with complex equipment may take some time and practice is essential.

Video courtesy of Sher AM. (2022). Slit lamp examination

Tonometry

Although not a standard technique used in the ED, due to the difficulties associated with formal intra-ocular pressure measurement with an application tonometer, the development of hand held devices (e.g. Tono-Pen) make this measurement easier and more accessible to the Emergency Physician.

• Although two thirds of eye problems presenting to the ED can be managed without ophthalmology input, assessment of these patients by junior doctors in the ED is poor. (level of evidence 4)
• A thorough history will provide important clues to the diagnosis in all of the common presentations of eye problems to the ED. (level of evidence 5)
• Measurement of the visual acuity is mandatory but may be inaccurate if the chart is not placed at the correct distance and well illuminated. (level of evidence 4)
• Pupil size is best measured using a standard scale and in a bright room normally ranges in size between 2 and 5 mm. (level of evidence 3b)
• Approximately 20% of the population has unequal pupils which are usually more pronounced in the dark. (level of evidence 3b)
• Examination of pupil reflexes must include exclusion of a relative afferent pupillary defect which indicates retinal or optic nerve pathology. (level of evidence 5)
• Visual field assessment can accurately localise a lesion of the optic pathway. (level of evidence 5)
• Proxymetacaine is the least painful local anaesthetic agent used in eye assessment and treatment. (level of evidence 2b)
• Tropicamide should be used prior to fundoscopy as it enables a more thorough examination and is associated with an extremely small risk of precipitating acute glaucoma. (level of evidence 2a)

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