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Fig. 8.4 Normal and abnormal refraction by the cornea and lens.

A Emmetropia (normal refraction). Cornea and lens focus light on the

retina. B Hypermetropia (long-sightedness). The eye is too short and the

image on the retina is not in focus. A convex (plus) lens focuses the image

on the retina. C Myopia (short-sightedness). The eye is too long and the

image on the retina is not in focus. A concave (minus) lens focuses the

image on the retina. D Myopia corrected using a pinhole. This negates

the effect of the lens, correcting refractive errors by allowing only rays from

directly in front to pass.

154 • The visual system

Fig. 8.5 Visual field defects. 1, Total loss of vision in one eye because of a lesion of the optic nerve. 2, Bitemporal hemianopia due to compression of

the optic chiasm. 3, Right homonymous hemianopia from a lesion of the optic tract. 4, Upper right quadrantanopia from a lesion of the lower fibres of the

optic radiation in the temporal lobe. 5, Lower quadrantanopia from a lesion of the upper fibres of the optic radiation in the anterior part of the parietal lobe.

6, Right homonymous hemianopia with sparing of the macula due to a lesion of the optic radiation in the occipital lobe.

Light source

Short ciliary nerve

Ciliary ganglion

III nerve

Edinger–Westphal nucleus

Lateral geniculate body

Posterior commissure Superior

colliculus

Midbrain

Optic nerve

A B Posterior

hypothalamus

First-order neuron

Second-order neuron

Internal carotid artery

Superior cervical ganglion

External carotid artery

Carotid plexus

Trigeminal nerve

Long ciliary

nerve

Müller’s muscle

Pupil dilator

Ciliospinal centre of Budge

(C8–T2)

Fig. 8.6 Pupillary innervation. A Parasympathetic pathway.

B Sympathetic pathway.

The history • 155

8

Red eye

The eye is covered in a network of vessels in the conjunctiva, episclera

and sclera. Ciliary vessels are also found around the cornea. Dilatation

or haemorrhage of any of these vessels can lead to a red eye.

Additionally, in uveitis, acute angle-closure glaucoma and corneal

irritation the ciliary vessels around the cornea become more prominent

(a ‘ciliary flush’). The appearance is distinct from conjunctivitis, in

which there is a relative blanching of vessels towards the cornea.

Ask:

• if the eye is painful or photophobic

• if vision is affected

• if there has been any recent trauma

• whether the eye is itchy

• whether there is any discharge

• whether there has been any recent contact lens wear or

foreign body exposure.

Box 8.4 summarises the features of the common causes of

a red eye on history and examination.

Double vision (diplopia)

Decipher whether the diplopia is monocular or binocular. Binocular

diplopia is caused by an imbalance in eye movement. Monocular

diplopia results from intraocular disease in one eye. There are

several causes of double vision (Box 8.5 and Figs 8.9 and 8.10).

Ask:

• whether the double vision occurs in one or both eyes

• about the character of the double vision, and whether the images

are seen side by side, one above the other or at an angle

• whether the double vision is associated with any recent

trauma.

Test the eye movements (see Fig. 8.11), and use your

knowledge of the function of the extraocular muscles (see Fig. 8.2)

to work out which cranial nerve is affected in binocular diplopia.

Discharge

Increasing discharge from the eye results from either an increase

in production or a decrease in drainage from the ocular surface.

Irritation of corneal nerves activates cranial nerve V(I) and results

in a reflex tearing response.

Tears normally drain through the punctum at the medial end of

the lower eyelid into the nasolacrimal duct, which opens below the

inferior turbinate into the nasal cavity. Blockage of tear drainage

or abnormal lid position can also result in excessive discharge.

Ask:

• whether the discharge is clear or opaque

• whether there is associated pain, foreign body sensation

or itchiness

• whether the patient has noticed other abnormalities, such

as red eye.

There are many causes of eye discharge, and their clinical

features are summarised in Box 8.6.

Swollen eyes

The orbit is an enclosed structure, except anteriorly. Any swelling

inside the orbit can lead to proptosis or anterior displacement

of the globe.

Ask if:

• the swelling is unilateral or bilateral

• the changes were acute or gradual

• the swelling is painful

• there is any itchiness or irritation

• the swelling is associated with any double vision.

Box 8.7 summarises the common causes of swollen eyes.

The history

When taking an ophthalmic history, bear in mind the anatomy

of the eye and visual pathways. This will enable you to work

from ‘front to back’ to include or exclude differential diagnoses.

Common presenting symptoms

Start the ophthalmic history with open questions. This builds rapport

with the patient by allowing them to describe the condition in their

own words, and provides clues for more directed questions later.

The visual system has its own set of presenting symptoms,

which prompt specific sets of questions. The most common

are described here.

Altered vision

Vision may be altered by an intraocular disease that leads

to a change in the optical or refractive properties of the eye

and prevents incident light rays from being clearly focused on

the retina. Alternatively, it may result from extraocular factors

associated with damage to the visual pathway, which runs from

the optic nerve to the occipital lobe (see Fig. 8.5).

Establish whether the change in vision is sudden or gradual,

as these will have their own specific set of differential diagnoses

(Box 8.1 and Fig. 8.7; Box 8.2 and Fig. 8.8).

Vision may be not just reduced but also distorted. This

results from disruption to the normal structure of the macula,

the central part of the retina. The most common cause is macular

degeneration but it may also frequently stem from an epiretinal

membrane, vitreous traction or central serous retinopathy.

Flashes and floaters result from disturbance of the vitreous and

the retina, occurring most commonly in posterior vitreous detachment. This is usually found in older patients as the vitreous

gradually degenerates and liquefies, causing it to peel off from the

retina. The vitreous is attached to the retina in certain regions; in

these regions the vitreous either detaches with traction, resulting

in flashing lights, or detaches by tearing the retina, releasing

retinal pigment cells. Patients will see either of these as floaters.

Haloes are coloured lights seen around bright lights. They

occur with corneal oedema and are most commonly associated

with angle-closure glaucoma.

When patients present with a change in vision, ask:

• Did the change in vision start suddenly or gradually?

• How is the vision affected (loss of vision, cloudy vision,

floaters, distortion)?

• Is it one or both eyes that are affected?

• Is the whole or only part of the visual field affected?

• If partial, which part of the visual field is affected?

Pain

Ask: