diagnosis of optic disc pallor is summarised in Box 8.11.

• Conversely, if the eye moves outwards when the

contralateral eye is covered, this suggests that it was

abnormally positioned inwards and is described as an

esotropia (convergent manifest squint).

• Repeat the cover/uncover test for the other eye.

• Failure of an eye to move despite an obvious corneal light

reflex may indicate that the eye has such poor vision that

it cannot take up fixation or else it is restricted from

moving.

• The alternating cover test involves covering the eyes

alternately and quickly while the patient is fixated on the

pen torch. Leave the cover on each eye for about 2

seconds but move between the eyes in less than 1

second. The movement is repeated multiple times. This

test will help to elicit latent squint.

Ocular movements

Examination sequence

• In the same seating position, ask the patient to look at a

target or pen-torch light about 50 cm away.

• Ask them to say if and when they experience diplopia.

• Starting from the primary position, move the target in the

six positions of gaze (see Fig. 8.11) and up and down.

• If diplopia is present, ask whether this is horizontal, vertical

or a combination of the two.

• Determine where the image separation is most

pronounced.

• Look for nystagmus and determine whether the eye

movement is smooth.

Interpretation of any limitation of excursion is made by

reference to the functions of the extraocular muscles (see

Fig. 8.2).

Oculocephalic (doll’s-eye) reflex

This reflex is the ability of the eyes to remain fixated while the

head is turned in the horizontal plane (Fig. 8.15). An impaired

reflex indicates a brainstem abnormality.

Examination sequence

• With the patient supine, ask them to look at your face.

Gently turn their head from side to side, noting the

movement of the eyes.

• This can also be performed on a comatose patient.

Nystagmus

Nystagmus is continuous, uncontrolled movement of the eyes.

Biphasic or jerk nystagmus is the most common type. It is

characterised by slow drift in one direction, followed by fast

correction/recovery in the opposite direction. The direction of the

fast phase designates the direction of the nystagmus. If there

are equal oscillations in both directions, it is called pendular

nystagmus.

Nystagmus commonly indicates vestibular disease, and the

examination sequence and differential diagnosis are covered

on page 174.

Investigations • 165

8

Retinopathies

Diabetes mellitus leads to a wide range of important abnormalities

in the retina, which are summarised on Fig. 8.17.

The eye also provides an opportunity to view the effects of

hypertension on the microvasculature. The retinal arteries are

effectively arterioles. Chronic arteriosclerosis with vessel-wall

thickening and hyalinisation appears as widening of the arterioles,

arteriovenous nicking where arterioles cross venules, and a ‘silver

and copper wiring’ light reflex.

More acute changes can also be seen in malignant hypertension.

Various grading systems have been created to try to link retinal

findings to end-organ damage. The retinal appearances in

hypertension are illustrated in Fig. 8.18 and classified using the

Modified Scheie classification:

• Grade 0: no changes.

• Grade 1: barely detectable arteriolar narrowing.

• Grade 2: obvious retinal arteriolar narrowing with focal

irregularities.

• Grade 3: grade 2 plus retinal haemorrhages, exudates,

cotton-wool spots or retinal oedema.

• Grade 4: grade 3 plus optic disc swelling.

Inherited retinopathies result from a wide range of genetic

mutations. The most common inherited retinopathy is retinitis

pigmentosa, which causes symptoms of nyctalopia (difficulty

seeing in dim light) and tunnel vision. Examination reveals a

pale optic disc, attenuated arterioles and bone-spicule retinal

pigmentation (see Fig. 8.8E).

Investigations

Appropriate initial tests for a variety of common presenting eye

problems are summarised in Box 8.12.

Fig. 8.15 Oculocephalic reflex. Move the head in the horizontal plane. Note that the eyes move in the opposite direction to head movement.

A

B

Fig. 8.16 The normal fundus. A Caucasian. B Asian.

166 • The visual system

8.10 Causes of optic disc swelling

Unilateral

• Optic neuritis

• Anterior ischaemic optic

neuropathy

• Syphilis

• Lyme disease

• Bartonella infection

• Sarcoidosis

• Leukaemia

• Optic nerve glioma

• Secondary metastases

Bilateral

• Papilloedema

• Optic disc drusen

• Diabetic papillitis

• Pseudopapilloedema in

hypermetropes

• Hypertensive papillopathy

8.11 Differential diagnosis of optic disc pallor

Inherited

• Congenital optic atrophy, including Leber’s and Behr’s

End-stage glaucoma

Trauma

Compressive

• Orbital neoplasm

• Thyroid eye disease

• Orbital cellulitis

Neurological

• End-stage papilloedema • Devic’s disease

Metabolic

• Nutritional deficiency

• Toxic amblyopia

• Ethambutol

• Sulphonamide

• Diabetes mellitus

Vascular

• Central retinal artery occlusion • Giant cell arteritis

Inflammatory

• Meningitis • Postoptic neuritis

A B

C D

E F

Fig. 8.17 Retinal abnormalities in diabetes mellitus. A Diabetic maculopathy. B Background diabetic retinopathy. C Severe non-proliferative

diabetic retinopathy. D Proliferative diabetic retinopathy. E Proliferative diabetic retinopathy with a vitreous haemorrhage. F Previous panretinal laser

photocoagulation in treated proliferative diabetic retinopathy.

Investigations • 167

8

A B

C D