8.9 Causes of anisocoria

Dilated pupil

• Cranial nerve III palsy

• Pharmacological treatment

with a dilating agent (e.g.

tropicamide or atropine)

• Physiological

• Post-surgical

• Adie’s tonic pupil

Constricted pupil

• Horner’s syndrome

• Mechanical, e.g. secondary to

posterior synechiae in iritis or

trauma

• Physiological

• Late-stage Adie’s tonic pupil

• Pharmacological treatment

with a constricting agent (e.g.

pilocarpine)

The physical examination • 163

8

on the cornea in relation to the pupil. The reflections

should be symmetrical between the two eyes. Ask the

patient if they see a single or double light. If they see

double, this may indicate the presence of a squint, but not

seeing double does not exclude a squint. If the reflection

is on the nasal aspect of the pupil in one eye, this

suggests that the eye is deviated outwards and is

described as an exotropia.

• To confirm the presence of a squint, perform the cover/

uncover test:

• Ask the patient to look at the pen torch at all times and

then cover one eye.

• Look at the uncovered eye for any movement. It may

be helpful to repeat this several times.

• Inward movement of the uncovered eye suggests that

it was positioned abnormally outwards and is described

as an exotropia (divergent manifest squint).

• It is important to show the patient the red target and ask

them to report what colour they see. A dull or pale red

suggests colour desaturation, which may indicate optic

nerve dysfunction.

• When testing each quadrant with a red target, be sure to

explain to the patient that they should say when they first

see that the target is red and not when they first see it.

The target may be visualised before they appreciate the

red colour.

• To test the blind spot, place a red-tipped target

equidistant between the patient and yourself at the visual

fixation point.

• Move the target temporally until it disappears.

• Then move the target slowly up and down, as well as from

side to side, until it reappears. This allows you to compare

the patient’s blind spot with yours.

Ocular alignment and eye movements

The eyes are normally parallel in all positions of gaze except

for convergence. Any misalignment is referred to as a squint

(strabismus). Squints are described as manifest (tropia) if present

with both eyes open, or latent (phoria) if revealed only by covering

one eye. In addition, they can be concomitant (where the angle

of squint remains the same in all positions of gaze) or incomitant

(where the angle of squint deviation is greatest in a single position

of gaze). The latter is commonly the result of paralysis of particular

extraocular muscles.

Detection of squint

Examination sequence

• Sit directly facing the patient, approximately 1 metre away

and at a similar height.

• Check visual acuity as part of the examination.

• Look for any abnormal head posture such as head tilts

(seen in cranial nerve IV palsy) or head turns (cranial nerve

VI palsy). These signs may be subtle.

• Hold a pen torch directly in front of the patient and instruct

them to look at the light. Observe the reflection of the light

Fig. 8.13 Confrontation visual field testing. Sit facing

the patient, 1 metre away. To compare your visual field

(assumed normal) with the patient’s, present a white

target or wiggle your fingers at a point equidistant

between yourself and the patient in the periphery. Bring

the target inwards in the direction of the blue arrows,

asking the patient to alert you when they first see it. Test

each eye separately.

Fig. 8.14 Testing the central visual field. Sit facing the patient, 1 metre

away. Present a red target at a point equidistant between yourself and the

patient in the periphery, starting when you can first see the target as red.

Bring the target inwards in the direction of the blue arrows, asking the

patient to alert you when they first see the target as red. Test each eye

separately.

164 • The visual system

Ophthalmoscopy

The direct ophthalmoscope is a useful tool for assessing both the

anterior and the posterior segments of the eye. Pharmacological

pupil dilatation is essential for a thorough fundus examination,

though the optic disc can be examined sufficiently without

dilatation.

Examination sequence

• Ask the patient to sit upright and look at a distant target.

• When using the direct ophthalmoscope to examine

the patient’s right eye, hold it in your right hand and

use your right eye to examine. Hold it in your left

hand and use your left eye to examine the patient’s

left eye.

• Place your free hand on the patient’s forehead and brow,

as this will steady the head and improve your

proprioception when moving closer to the patient with the

ophthalmoscope.

• Rotate the ophthalmoscope lens to +10. This will allow

a magnified view of the anterior segment. You will be

able to examine the eyelid margins, conjunctiva, cornea

and iris. If epithelial defects are suspected, fluorescein can

be administered and a cobalt blue filter used to reveal

these.

• To examine the fundus, dial the lens back to 0.

• With your hand on the forehead and the brow, use the

ophthalmoscope to see the red reflex (red light reflected

off the retina) at a distance of about 10 cm. When the red

reflex is in focus, look for opacities and determine whether

they are static or mobile. Static opacities are usually due

to cataract changes, while mobile opacities indicate

vitreous opacities.

• Slowly move the ophthalmoscope closer to the patient

almost to the point that your forehead touches your

thumb, which is resting on the patient’s forehead and

brow (see Fig. 8.12).

• Turn the lens dial until the optic disc comes into focus; if it

does not, focus on a blood vessel.

• The optic disc can usually be located easily; if not, follow a

blood vessel centrally (in the direction opposite to its

branches) to locate it.

• Examine the optic disc, paying particular attention to its

shape, colour, edges and cup size.

• Follow each blood-vessel arcade and examine each of the

retinal quadrants.

• To examine the macula, ask the patient to look directly at

the light.

The normal retina looks different in Asian and Caucasian

patients (Fig. 8.16).

Swelling of the optic disc is a very important clinical sign.

Causes of unilateral and bilateral optic disc swelling, and their

distinguishing features, are summarised in Box 8.10.

A variety of diseases that can damage the optic nerve cause

an abnormally pale optic disc (see Fig. 8.8D). The differential