The visual system

Change in vision

Loss or reduced vision is the most common change. Patients often describe blurred vision. Ocular disease is the most common cause of a change in vision. Any intraocular condition that prevents light from activating retinal photoreceptors or the signal from photoreceptors reaching the optic nerve can cause altered vision. Rarely, damage to the extraocular visual pathway may cause altered vision (see Fig. 8.5 ).

When patients present with a change in vision, ask:

• Was the onset of visual change sudden or gradual? Sudden or gradual visual loss leads to specific differential diagnoses ( Box 8.1 and Fig. 8.7 ; Box 8.2 and Fig. 8.8 ). If sudden, then enquire about possible causes (e.g. trauma, foreign body, chemical injury).

  8.1

  Common causes of an acute change in vision

  Cause	Clinical features	Cause	Clinical features
  Unilateral
  Giant cell arteritis	Painless loss of vision Age >50 years Weight loss Loss of appetite, fatigue Jaw or tongue claudication Temporal headache Pale or swollen optic disc RAPD	Vitreous haemorrhage	Painless loss of vision Risk in proliferative diabetic retinopathy History of flashing lights or floaters may precede haemorrhage in posterior vitreous detachment Poor fundus view on examination Reduction or loss of the red reflex Usually no RAPD if retina is intact
  Central retinal vein occlusion	Acute, painless loss of vision May have RAPD if severe Greater risk if hypertensive Haemorrhages, exudates and tortuous retinal veins ( Fig. 8.7A )	Wet age-related macular degeneration	Sudden painless loss of central vision Age >55 years Increased risk in smokers Haemorrhage at the macula ( Fig. 8.7E )
  Retinal detachment	Painless loss of vision Association with flashing lights or floaters History of a curtain coming across vision Myopic patients at greater risk RAPD if macula is involved Pale raised retina usually with a retinal tear ( Fig. 8.7B )	Anterior ischaemic optic neuropathy	Painless loss of upper or lower visual field Increased risk in vasculopaths Examination may reveal optic disc swelling
  Central retinal arterial occlusion	Acute, painless loss of vision Carotid bruit may be heard RAPD Increased risk in vasculopaths Examination: pale retina with a cherry red spot at the fovea ( Fig. 8.7C )	Optic neuritis/retrobulbar neuritis	Visual reduction over hours Usually aged 20–50 Pain exacerbated by eye movement RAPD Reduced colour sensitivity Swollen optic disc in optic neuritis ( Fig. 8.7F ) or normal appearances in retrobulbar neuritis
  Corneal disease	Usually painful Foreign body sensation Corneal opacity may be visible (e.g. Fig. 8.7D )	Amaurosis fugax	Painless loss of vision for minutes History of cardiovascular disease May have associated atrial fibrillation or carotid bruit Normal ocular examination
  Bilateral
  Giant cell arteritis	Painless loss of vision Age >50 years Weight loss Loss of appetite, Fatigue Jaw or tongue, claudication Temporal headache Pale or swollen optic disc	Cerebral infarct	May have associated headache and/or neurological signs Usually specific field defects dependent on how the visual pathway is affected ( Fig. 8.5 ) Normal fundus examination If post chiasmal visual pathway affected, bilateral visual field abnormalities
  Raised intracranial pressure	Headache Often asymmetric Pulsatile tinnitus Swollen optic discs	Migraine	Gradually evolving usually bilateral visual loss Vision loss is usually preceded by visual aura Normal ocular examination Ocular examination: normal Vision usually returns to normal after hours

  RAPD, Relative afferent pupillary defect (p. 182).

  
  8.2

  Common causes of a gradual loss of vision

  Cause	Clinical features
  Refractive error	No associated symptoms Normal ocular examination Vision can be improved by pinhole ( Fig. 8.4D )
  Glaucoma	Usually bilateral but asymmetric loss of visual field Cupped optic discs on examination
  Cataract	Gradual clouding of vision May be associated with glare Usually seen in the elderly Examination: clouding of the pupil and altered red reflex ( Fig. 8.8A and B )
  Diabetic maculopathy	History of diabetes Central vision reduced or distorted Haemorrhages and exudates at the macula on examination ( Fig. 8.17A )
  Compressive optic neuropathy	Gradual unilateral loss of vision Pale optic disc on examination ( Fig. 8.8D )
  Retinitis pigmentosa	Gradual bilateral symmetric loss of peripheral visual field Nyctalopia (poor vision in dim light) Family history Examination: bone spicule fundus, attenuated blood vessels and waxy optic disc ( Fig. 8.8E )
  Dry age-related macular degeneration	Gradual loss of central vision Usually bilateral Examination: drusen, atrophy and pigmentation at the macula ( Fig. 8.8C )

  

• Does the vision change affect one or both eyes? Sudden onset of bilateral change in vision suggests a post chiasmal cause.

• Is the change in vision associated with any additional features (e.g. haloes, flashing lights, floaters, distortion, discharge, red eye, pain)? Haloes are bright or rainbow-coloured rings seen surrounding a light source. They occur when there is corneal oedema and are most commonly associated with angle-closure glaucoma. Flashes and floaters result from a disturbance of the vitreous–retinal interface, most commonly due to a posterior vitreous detachment. This usually occurs with age as the vitreous degenerates, liquefies and peels away from the retina, resulting in floaters. Detachment sometimes causes retinal traction, resulting in flashing lights. More rarely, posterior vitreous detachment causes a retinal tear (releasing cells seen as floaters), which may progress to retinal detachment with visual field loss. Distortion is most commonly seen in diseases of the macula, such as age-related macular degeneration, epiretinal membrane, vitreous traction on the retina or central serous retinopathy.

• Does the change in vison affect part or whole of the visual field? If part, which part? Specific types of visual field loss may point to retinal disease, such as macular degeneration, optic nerve disease such as glaucoma or visual pathway defects (see Fig. 8.5 ).

Pain

Ask:

• Can you describe the nature of the pain?

• How severe is it?

• Did anything cause the pain?

• Is pain exacerbated or relieved by anything?

• Any other associated features (e.g. change in vision, red eye, discharge, photophobia, watering eye)?

The most common cause of a painful eye is corneal irritation from a foreign body or infection. The cornea is one of the most highly innervated parts of the body. When the corneal nerves are activated, a patient experiences foreign body sensation, pain, reflex watering and photophobia. There are, however, many other causes of a painful eye. Box 8.3 summarises the history and examination findings associated with a painful eye.

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 (‘ciliary flush’). The appearance is distinct from conjunctivitis, in which there is classically a relative blanching of vessels around the cornea.

Ask:

• Is there any pain or photophobia?

• Is vision affected? If so, how?

• Has there has been any recent trauma or foreign body?

• Is the eye itchy?

• Is there any discharge? If so, what kind (e.g. watery, sticky, clear, yellow)?

• Has there been any recent contact lens use?

Box 8.4 summarises the features of the common causes of a red eye on history and examination.

Double vision (diplopia)

Ask:

• Does the double vision occur with one eye open or only with both eyes open? Binocular double vision is caused by an imbalance in eye movement between the eyes. Monocular diplopia results from intraocular disease in one eye.

• What is the character of the double vision (e.g. are images seen side by side, one above the other or at an angle)?

• Has there been any recent trauma?

In binocular diplopia, test the eye movements ( Fig. 8.9 ) and use your knowledge of the function of the extraocular muscles (see Fig. 8.2 ) to work out which cranial nerve is affected.

The causes of double vision are summarised in Box 8.5 and Figs. 8.10 and 8.11 .

Discharge

Ocular discharge 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), resulting in a reflex tearing response.

Tears normally drain from the ocular surface through the puncta, small openings to the medial end of the upper and lower eyelid, into the nasolacrimal duct, which opens below the inferior turbinate in the nasal cavity. Consequently, blockage of tear drainage or an abnormal lid position can also result in excessive discharge.

Ask:

• Is the discharge clear or opaque? If opaque, what colour?

• Is the discharge watery or sticky?

• Is the discharge associated with any other features (e.g. pain, foreign body sensation, red eye or itchiness)?

The clinical features of different types of eye discharge are summarised in Box 8.6 .

Swollen eyes

The orbit is enclosed by bone on all sides, except anteriorly. As a result, orbital swelling can lead to the anterior displacement of the globe and proptosis.

Ask if the swelling is:

• Unilateral or bilateral?

• Acute or gradual in onset?

• Associated with pain?

• Associated with itch or irritation?

• Associated with double vision?

Box 8.7 summarises the common causes of swollen eyes.