Introduction

Although, proportionally, a greater contribution towards the diagnosis of ophthalmic disorders is made by the examination compared to the history, it is important to obtain a detailed account of the presenting complaint and associated visual symptoms from the patient with an ocular problem.

History

Disturbance of vision, the most important ocular symptom, may be sudden or gradual, unilateral or bilateral, and lead to loss of central vision or partial field loss. Simultaneous, bilateral visual symptoms are usually due to disease in optic pathways at or posterior to the optic chiasm. Sudden visual disturbance should be assessed urgently. Visual halluci-nations may be formed or unformed. Some visual symptoms have particular significance (Table 19.1). For example, haloes around lights occur in acute angle-closure glaucoma due to corneal oedema. ‘Floaters’ and flashes (photopsia) are indicative of vitreous or retinal disorders, respectively. The latter may also cause objects to appear smaller (micro-psia), larger (macropsia) or distorted (metamorph-opsia). Disorders of ocular movement may cause double vision (diplopia) or visual blurring. Are the visual symptoms binocular or monocular? Are they related to eye movements?

Other common presentations include a red eye, abnormal lid position, protrusion of the globe, pupillary or eyelid abnormality. Ocular pain is often associated with a red eye (Table 19.2). Ocular pain due to a foreign body may be described as ‘a gritty sensation’ in the eye, often worsened by blinking. It may be associated with sensitivity to light (photophobia) but this, particularly in conjunction with ocular aching, usually indicates serious corneal or intraocular disease. Severe ocular pain with vomiting may indicate acute glaucoma. Migraine often presents with bilateral visual symptoms and headache. Raised intracranial pressure and giant cell arteritis should also be considered when headache is associated with visual symptoms. Pain may be referred to the eye because of neighbouring disease, for example sinusitus. Excessive tear production (lacrimation) associated with discomfort may indicate ocular surface disease. There may be abnormal secretions from the eye, such as mucus or pus. With insufficient tears, the eye typically feels dry, whereas a painless overflow of tears (epiphora) typically indicates blockage of the lacrimal drainage system.

Table 19.2 Red eye

FB, foreign body; PMH, past medical history; URTI, upper respiratory tract infection.

Note any previous ophthalmic history, such as a squint in childhood, and any pre-existing poor vision, or previous ocular injury or surgery. Note what type of glasses or contact lenses are worn: extended-wear soft contact lenses are associated with an increased risk of corneal infection. The family history may reveal glaucoma, decreased visual acuity, colour blindness, squint, or neurological disease associated with visual loss. In addition to the ocular history, the medical, drug and social histories are important.

Examination

Eye examination is part of the cranial nerve examination. It includes ocular movements (cranial nerves III, IV and VI), corneal sensation (ophthalmic division of the trigeminal nerve) and eye closure (VII). Assess the optic (II) nerve by testing visual acuity, colour vision, the visual fields and the pupillary light reaction. Inspect the optic nerve head (the optic disc and cup) with the ophthalmoscope. Detailed examination of the anterior segment of the eye requires use of the slit lamp which, with additional equipment, can also be used to test the intraocular pressure (IOP) and examine the retina.

Visual acuity

Visual acuity is most reliably tested at 6 m (20 ft) using a standard chart such as the Snellen chart (Fig. 19.1). Tests of acuity in near vision are portable but limited by age-related loss of accommodation (presbyopia), which necessitates refractive correction in older patients. These use test types of varying sizes, based on the point system of the printers (Fig. 19.2), and the smallest type that can be read comfortably at a distance of 33 cm is recorded (normally N4.5 or N5 type).

Figure 19.1 Snellen chart for testing distance vision.

Figure 19.2 Near vision chart based on the point system of the printer.

Snellen distance vision

On the Snellen chart, each line of letters is designated by a number that corresponds to the distance at which those letters can be read by someone with ‘normal’ distance vision. For example, the largest letter, at the top of the chart – designated 60 – would be read at 60 m by a person with ‘normal’ vision.

Technique

The patient sits or stands 6 m (20 ft) from the chart. Where space is limited, a mirror may be used 3 m from both patient and chart, with the patient facing away from the chart and reading the letters in the mirror, giving a total of 6 m. Distance glasses should be worn if necessary, and each eye tested separately. The patient should read line by line from the top of the chart. If a patient cannot see the largest letter, designated 60, then the test distance should be reduced. If at 1 m the 60 letter cannot be seen, assess the following:

Counting fingers held up at about 1 m (CFs).

Hand movements (HMs).

Perception of light (PL).

When testing low vision, ensure that the eye not being tested is completely covered. If a patient cannot read 6/6 or better in either eye, check the vision again using a pinhole occluder (Fig. 19.3). This test distinguishes patients with poor vision due to refractive error from those who have ocular or neurological conditions. In a myopic (short-sighted) eye, the rays of light are focused in front of the retina. In hypermetropia (long-sightedness), light is focused behind the eye, because the eye is abnormally short. In astigmatism, the cornea is not uniformly curved and light is not focused evenly on the retina. When using a pinhole, only the central rays of light pass through to the retina and the above refractive errors are significally reduced.

Figure 19.3 Testing vision with a pinhole. Top: light is not focused on the retina owing to refractive error (in this case in front of the retina, as in myopia; short-sightedness). Bottom: the use of a pinhole selects rays of light not needing to be focused, giving a better indication of a patient’s true best corrected visual acuity despite refractive error.

Recording visual acuity

The top figure, the numerator, records the distance of the subject from the test chart – usually 6 m. The bottom figure records the line read by the patient. The normal person can read the line designated 6 at 6 m (i.e. 6/6 (20/20) vision).

Record a mistake of one letter in a line as ‘ −1’ and a single letter read from the next smaller line as ‘+1’. Thus, if all except one of the letters on the line designated 6 are read correctly, the visual acuity is recorded 6/6 −1. If only one letter on that line is read correctly, the visual acuity is recorded 6/9 +1. Like all ophthalmic findings except visual fields, right eye visual acuity is traditionally written on the left side of the page (as the patient’s eye appears to you), and vice versa. Whether the patient was using glasses, pinhole (ph) or was unaided (ua) is recorded in the middle (Fig. 19.4).

Figure 19.4 Recording visual acuity: the numerator is the test distance. ph, pinhole.

Colour vision

Tests of colour vision are important because colour perception, especially for red, is affected in optic nerve disease before changes in visual acuity can be detected. Show the patient a red target one eye at a time (any bright red target can be used) and ask if there is a difference between the eyes. In the affected eye, red appears ‘washed out’ (desaturated). Acquired defects of colour vision may also occur in macular disease. The Ishihara test (Fig. 19.5) was devised to test for congenital colour anomalies (colour blindness), but is often used to assess acquired visual disorders. Most inherited colour blindness occurs in males (sex-linked recessive inheritance). It ranges from total colour blindness (monochromatopsia) to subtle confusion between colours, typically between red and green. About 8% of men and 0.5% of women in the UK have congenital colour perception defects. Blue/yellow deficiencies and total colour blindness are uncommon.

Figure 19.5 Ishihara colour vision test.

Visual field testing

Visual field testing is described in Chapter 14. Field defects may affect one or both eyes. Symmetric bilateral (homonymous) field defects are characteristic of lesions posterior to the optic chiasm, and asymmetric field defects are usually due to lesions anterior to the chiasm (i.e. in the optic nerves or retinae). Characteristic field defects (scotoma) occur in glaucoma, when damage to nerve fibres occurs at the optic disc, typically at the inferior or superior aspect of the optic cup. Fundoscopy shows an increase in vertical length of the optic cup (see later in the chapter for details about how examine the fundi) and field loss is arc-shaped (arcuate scotoma). If both the inferior and superior fields are involved, a ring-shaped scotoma develops. Untreated glaucoma results in loss of the peripheral field so that only a small central island of vision remains (tunnel vision). Computerized perimetry is useful in identifying early visual field loss. The Humphrey field test analyser, for example, provides statistical information indicating the reliability of the test in comparison with a group of age-matched controls (Fig. 19.6).

Figure 19.6 Automated static perimetry: the Humphrey field test analyser.

Pupils

Examination of the pupils in neurology is discussed in Chapter 14. In ophthalmic practice, there are three key aspects to pupil examination: size, shape and reactions.

Pupil size: anisocoria

In 12% of normal individuals, the pupils are slightly unequal, particularly in bright light (anisocoria), but in these subjects they react normally. Abnormal pupils dilate and constrict abnormally, and the degree of anisocoria varies with the ambient illumination. However, it is often difficult to decide which pupil is abnormal. In the absence of local eye disease, a small pupil may be due to paralysis of the dilator pupillae muscle (sympathetic innervated), part of Horner’s syndrome (Fig. 19.7), in which anisocoria is more pronounced in low ambient light. An enlarged pupil suggests a parasympathetic lesion, which may be preganglionic in oculomotor lesions or postganglionic as in the tonic pupil of Adie’s syndrome. Adie’s tonic pupil tends to be dilated in bright light and is very slow to react. A feature of both parasympathetic and sympathetic lesions is denervation hypersensitivity caused by upregulation of receptors at the neuromuscular junction (adrenergic in sympathetic and cholinergic in parasympathetic). This is the basis of pharmacological pupil testing. In both pre- and postganglionic parasympathetic blockade, the pupil is supersensitive to weak cholinergic drops (e.g. pilocarpine 0.1%). In sympathetic block, dilute adrenergic agonists such as phenylephrine 1% are unreliable, so the uptake blocker, cocaine 4%, is used. This dilates normal pupils but has no effect in pre- or postganglionic lesions. Hydroxyamfetamine 1% causes noradrenaline (nor-epinephrine) release from normal or intact postganglionic neurones and allows pre- and postganglionic lesions to be distinguished (the synapse is located in the superior cervical ganglion). In complex pupil abnormalities, for example bilateral Horner’s syndrome, infrared pupil imaging can be valuable. Causes of anisocoria are highlighted in Box 19.1. In congenital Horner’s syndrome, the affected iris is depigmented and appears blue.

Figure 19.7 Horner’s syndrome. On the affected side there is ptosis, which may be very slight, and a small pupil (miosis) that reacts to both light and accommodation.

(Reproduced with permission from Mir, 2003 Atlas of Clinical Diagnosis, 2nd edn, Saunders, Edinburgh.)

Box 19.1 Causes of anisocoria

Idiopathic (12% population)

Parasympathetic:

– third nerve palsy (external ophthalmoplegia)

– tonic pupil (internal ophthalmoplegia, e.g. Holmes-Adie)

Sympathetic:

– Horner’s syndrome

Argyll Robertson

Pharmacological

Ocular:

– iris inflammation, e.g. iritis

– iris ischaemia

– trauma

– iatrogenic

Pupil reactions: afferent and central defects

The swinging light test is used to detect a relative afferent pupillary defect (RAPD) resulting from retinal or optic nerve disease. The test loses sensiti-vity in symmetrical bilateral optic nerve disease, but this is rare, and in most bilateral cases the defect will be detected on the more abnormal side. RAPD is often associated with reduced vision, but if central vision is retained, the acuity will be normal, although severe peripheral field damage may cause RAPD. In neurosyphilis, the pupils are small and irregular and show the Argyll Robertson phenomenon (normal pupil constriction to a near target but reduced reaction to light) owing to a midbrain defect. In Parinaud’s syndrome, the pupils are typically large and poorly reactive to light, with abnormal vertical gaze, convergence retraction nystagmus and lid retraction on attempted upgaze (Collier’s sign). The causes of light-near dissociation are given in Box 19.2.

Box 19.2 Light-near dissociation

Argyll Robertson pupil

Holmes-Adie pupil

Parinaud’s syndrome

Aberrant third nerve regeneration

Myotonic dystrophy

Diabetes mellitus

Pupil shape

Slit-lamp examination is the best technique to assess intrinsic ocular disease that may affect the shape and position of the pupil (Box 19.3).

Box 19.3 Causes of abnormal pupil shape

Congenital: Rieger’s anomaly (anterior segment cleavage anomalies)

Trauma

Iatrogenic (sphincterotomies, iridectomy, cataract surgery)

Inflammatory (posterior synechiae in iritis)

Tumour (ectropion uveae in ciliary body malignancies)

Ischaemic: herpes zoster, angle-closure glaucoma

Idiopathic: iridocorneal endotheliopathy (ICE) syndrome (which also features multiple pupils (polycoria) and misplaced pupils (correctopia))