• If the patient cannot see the largest font, reduce

the test distance to 3 metres, then to 1 metre if

necessary.

• If they still cannot see the largest font, document

instead whether they can count fingers, see hand

movement or just perceive the difference between light

and dark.

• On the Snellen chart, lines of decreasing font size are

numbered according to the distance in metres that a

person with normal vision could read them. Express

visual acuity as the distance at which text is read

(usually 6 metres) over the number of the smallest font

line read correctly on the chart. For example, 6/60

means that the patient sees at 6 metres the font size

that is seen at 60 metres by a person with normal

vision.

• If the patient cannot read down to line 6 (6/6), place a

pinhole directly in front of the eye (with the patient keeping

their usual spectacles on, if they wear them) to correct any

residual refractive error (see Fig. 8.4D).

• If the visual acuity is not improved with a pinhole, this

indicates the presence of eye disease not related to the

refractive apparatus alone, such as retinal or optic nerve

pathology.

• Note that 6/6 is regarded as normal vision; in the UK,

6/12 or better with both eyes is the requirement for

driving.

• Assess near vision with a similar test using text of

reducing font size held at a comfortable reading

distance. It is important to consider the need for

reading spectacles in patients over the age of 40 years

because of presbyopia (age-related deterioration in

near vision).

The physical examination • 161

8

If the degree of anisocoria is greater in brighter lighting, then

it is the larger pupil that is abnormal; if it is more pronounced

in dim lighting, the smaller pupil is the abnormal one. An equal

degree of anisocoria in all levels of lighting indicates physiological

anisocoria.

Direct and consensual light reflex

Examination sequence

• With the patient fixating on a point in the distance and in

ambient lighting, shine a bright light from the temporal side

into one eye and look for constriction of the ipsilateral

pupil.

• To test the consensual reflex, assess the pupil response in

the contralateral pupil when light is directed towards the

ipsilateral pupil. Repeat for the other pupil.

Orbit and periorbital examination

Examination sequence

• Observe the face and orbit for asymmetry and any obvious

abnormality, including swelling, erythema or any other skin

changes.

• Look for any abnormality in the position of the lids and

ptosis (Box 8.8).

• Look for any asymmetry in the position of the eyeballs.

Eyeball protrusion (proptosis) is best detected by looking

down on the head from above.

• Palpate around the orbital rim and orbit, looking for any

masses.

• Check eye movements (Fig. 8.11).

• Use an ophthalmoscope (Fig. 8.12) to look for optic disc

swelling from compression.

Pupils

First inspect generally for squint and ptosis. Examine pupil shape

and symmetry. Physiological anisocoria (unequal pupil size) is

seen in 20% of the population.

Anisocoria

The eyes should be assessed to determine which is the abnormal

pupil.

Examination sequence

• With the patient fixating at a point in the distance, increase

and decrease the illumination and look for any change in

the degree of anisocoria.

8.8 Causes of eyelid ptosis

Cause Diagnosis

Associated distinguishing

features

Neurogenic Horner’s syndrome Ptosis, miosis, eye

movement spared

Cranial nerve III

palsy

Dilated pupil, eye

movements affected (see

Fig. 8.10)

Myogenic Myotonic dystrophy Frontal balding, sustained

handgrip

Chronic progressive

external

ophthalmoplegia

Bilateral ptosis and

impairment of eye

movements, often without

diplopia, sparing of pupil

reflexes

Oculopharyngeal

dystrophy

History of swallowing

abnormalities

Neuromuscular

junction

Myasthenia gravis History of variable

muscular fatigue

Mechanical Eyelid tumour Evident on inspection

Eyelid inflammation/

infection

Evident on inspection

Trauma Scarring/history of trauma

Degenerative Levator aponeurosis

degeneration

Often unilateral, eye

movement normal

Long-term contact

lens wear

History of contact lens use

Fig. 8.12 Ophthalmoscopy. Ask the patient to focus on a distant target.

To examine the left eye, use your left eye to look through the

ophthalmoscope and left hand to hold it, index finger on the wheel. Hold

the patient’s head with your free hand. Gradually move in to visualise the

optic disc. Rotate the wheel to obtain a clear, focused image.

Fig. 8.11 Testing the six positions of gaze. Sit facing the patient, 1

metre away. Perform the test with both eyes open. Hold a pen torch or

target in front of the patient and ask them if they see the target as double.

Move the target to the six positions of gaze (blue arrows).

162 • The visual system

Adie’s pupil

This is a mid-dilated pupil that responds poorly to both light

and accommodation. With time, however, the affected pupil

can become constricted. Adie’s pupil is thought to result from

parasympathetic pathway dysfunction in the orbit. It typically

affects young women and is benign. When associated with

diminished Achilles tendon reflexes, it is referred to as Holmes–

Adie syndrome.

Argyll Robertson pupil

The pupil is small and irregular, and reacts to accommodation

but not light. This is classically the result of neurosyphilis. There

are other causes of light-near dissociation, however, including

diabetes mellitus, severe optic nerve disease and midbrain

lesions.

Visual fields

The normal visual field extends 160 degrees horizontally and

130 degrees vertically. Fixation is the very centre of the patient’s

visual field. The physiological blind spot is located 15 degrees

temporal to the point of visual fixation and represents the entry

of the optic nerve head into the eye.

The aim of the visual field examination is to test the patient’s

visual fields against your own (making the assumption that you

have normal visual fields). The visual field can be tested using

the fingers for gross examination. Finer examination can be

performed using a small hatpin.

Examination sequence

• Check visual acuity and ensure that the patient has at

least enough vision to count fingers.

• Sit directly facing the patient, about 1 metre away.

• With your eyes and the patient’s eyes open, ask the

patient to look at your face and comment on whether they

have any difficulty seeing parts of your face.

• Ask the patient to keep looking straight at your face. Test

each eye separately. Ask the patient to close or cover one

eye and look directly across to your opposite eye; you

should also close your other eye.

• Hold your hands out and bring an extended finger in

from the periphery towards the centre of the visual field.

For an accurate assessment of the patient’s fields, it is

vital that the testing finger is always kept in the plane

exactly halfway between yourself and the patient. Wiggle

your fingertip and ask the patient to point to it when they

first see it (Fig. 8.13). If the patient fails to notice your finger

when it is clearly visible to you, their field is reduced in

that area.

• Test all four quadrants separately.

• More subtle visual field defects can be elicited using a

small white hatpin or a white Neurotip. With the patient

looking directly at your eye, bring the white target in from

the periphery to the centre (again always in the plane

halfway between you and the patient). Ask the patient to

say when they first see the target.

• Undertake this for all four quadrants, testing each eye

separately.

• To assess very early visual field loss, repeat the same test

using a red hatpin or a red Neurotip (Fig. 8.14).

Relative afferent pupillary defect

Relative afferent pupillary defect (RAPD) is an important clinical

sign that occurs when disease of the retina or optic nerve reduces

the response of the eye to a light stimulus. Testing for RAPD

is an extension of the direct and consensual light responses.

Examination sequence

• Use a bright light source.

• Move the light briskly from one eye to the other, but place

it on each eye for a minimum of 3 seconds.

In normal patients, this results in symmetrical constriction of

both pupils. In RAPD, light in the affected eye causes weaker

constriction (apparent dilatation) compared to light shone in the

normal eye.

Accommodation

Examination sequence

• Ask the patient to look at a close fixation target (do not

use a light source) after fixating on a distant target.

• There should be constriction of the pupil on near gaze.

• Failure to constrict to light but constriction on near gaze is

referred to as light-near dissociation.

There are many causes of a dilated or constricted pupil

(Box 8.9).

Pupillary examination will distinguish the various causes of

anisocoria, as described here.

Horner’s syndrome

Horner’s syndrome is the clinical picture resulting from dysfunction

of sympathetic nerve supply to the eye, which originates in the

hypothalamus and emerges in the root of the neck before

innervating the pupil (see Fig. 8.6B). Damage at any point in

this pathway will result in Horner’s syndrome. On examination,

there is a constricted pupil (loss of sympathetic dilator tone) and

a partial ptosis resulting from denervation of Müller’s muscle

in the upper eyelid. There may also be anhydrosis (loss of

sweating) on the affected side. Diagnosis may be confirmed by

administering cocaine eye drops, which will cause pupil dilatation

in the unaffected pupil but no dilatation on the affected side.

Causes of Horner’s syndrome include demyelination, neck trauma/

surgery, apical lung tumour (Pancoast tumour) and carotid artery

dissection.