Eye and Vision OSCE Examination

Contents

1. Introduction
2. General Inspection
3. Visual Acuity
4. Colour Vision
5. Pupillary Reflexes
6. Visual Fields
7. Eye Movements
8. Fundoscopy
9. Completing the Examination
10. Quiz

Introduction

Wash your hands and don personal protective equipment if appropriate.

Introduce yourself to the patient and ensure to mention your grade e.g. 3rd year medical student/junior doctor/consultant.

Confirm the patient’s details taking 3 points of identification usually; full name, date of birth and NHS/hospital number.

Obtain consent for the examination, ensuring to explain what the examination will entail. A useful framing is to say you would like to check the patient’s vision, how their eyes move and look at the back of the eyes.

Position the patient sitting comfortably in a chair, ideally facing you at roughly the same eye level for the parts of the examination performed face-to-face.

Ask the patient whether they normally wear glasses or contact lenses, particularly distance glasses, as these will be needed for an accurate assessment of visual acuity. Also ask if they have any eye pain before you begin.

General Inspection

Begin with a general inspection of the patient and the area around them. Look for obvious clues to the underlying diagnosis such as a white stick or guide dog (suggesting significant visual impairment), glasses or contact lens equipment, an eye patch, a magnifier or large-print material, or a prosthetic eye. These adaptations give an immediate sense of how the patient’s vision affects their daily function.

Inspect the face and eyes for any asymmetry. A facial droop may indicate a previous stroke or facial nerve palsy, which is relevant because incomplete eyelid closure can threaten the cornea. Look at the position of the eyes for any obvious squint (strabismus) or proptosis (bulging of the eye), the latter classically associated with thyroid eye disease.

Inspect the eyelids for ptosis (drooping of the upper eyelid). Ptosis can be caused by a third cranial nerve (oculomotor) palsy or Horner’s syndrome, and the associated features help to distinguish them – a third nerve palsy tends to cause a complete ptosis with a ‘down and out’ eye and a dilated pupil, whereas Horner’s syndrome causes a partial ptosis with a constricted pupil.

Look at the eyes themselves for any redness (suggesting conjunctivitis, scleritis or an acute red eye), discharge, abnormal pupil size or shape, and the presence of corneal arcus (a pale ring around the iris caused by lipid deposition, which can indicate hyperlipidaemia in younger patients).

Visual Acuity

Visual acuity is the sharpness of central vision and is the single most important measurement in an eye examination. It is assessed using a Snellen chart positioned at 6 metres from the patient (or at 3 metres using a mirror). If the patient normally wears distance glasses, these should be worn, as you are testing their best corrected vision.

Test each eye separately, asking the patient to cover the other eye and read down the chart until the letters can no longer be made out. Record each eye individually, noting whether glasses were worn.

Visual acuity is recorded as a fraction, for example 6/6. The top number is the distance the patient was from the chart (6 metres), and the bottom number is the distance at which a person with normal vision could read that same line. So 6/6 is normal vision, while 6/60 means the patient can only read at 6 metres what a normal-sighted person could read at 60 metres – markedly reduced acuity.

If the patient cannot read the top letter of the chart even at 6 metres, the assessment is stepped down: move the patient to 3 metres, then 1 metre, then test counting fingers, hand movements, and finally perception of light. This grading describes exactly how poor the vision is and is important for documentation and for assessing severe disease.

If acuity is reduced, repeat the test with the patient looking through a pinhole. A pinhole allows only the central, most focused rays of light to reach the retina. If vision improves with a pinhole, the cause is most likely a refractive error (the eye is simply out of focus, correctable with glasses). If it does not improve, this points towards a pathological cause such as cataract, macular disease or optic nerve pathology.

Image - A Snellen chart, used to assess distance visual acuity. The patient reads down the chart at a set distance, and acuity is recorded as a fraction such as 6/6

Creative commons source by Jeff Dahl [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]

Near vision should also be assessed, using a near reading chart held at a comfortable reading distance with the patient wearing any reading glasses. Reduced near vision with preserved distance vision is common in presbyopia, the age-related loss of accommodation.

Colour Vision

Colour vision is assessed using Ishihara plates. Each plate is made up of coloured dots arranged so that a number is visible to those with normal colour vision but is difficult or impossible to identify for those with a colour vision deficit.

The patient is asked to identify the number on each plate, testing one eye at a time. The first plate is usually a ‘test plate’ visible to everyone, including those with colour blindness, which checks the patient has understood the task and has adequate acuity to see the dots.

Although Ishihara plates were originally designed to detect congenital red-green colour blindness, in the context of an eye examination they are valuable because acquired colour vision loss – particularly loss of red desaturation – is an early and sensitive sign of optic nerve disease, such as optic neuritis. A patient with optic neuritis may report that a red object looks washed-out or less vivid in the affected eye, and may struggle with the Ishihara plates on that side even when acuity is relatively preserved.

Image - An Ishihara plate. The number formed by the coloured dots is readily seen by those with normal colour vision but not by those with a colour vision deficit

Creative commons source by Shinobu Ishihara [Public domain]

Pupillary Reflexes

Before testing the reflexes, inspect the pupils at rest for their size, shape and symmetry. Most people have pupils of roughly equal size; a difference between the two is termed anisocoria.

Understanding the light reflex pathway makes interpreting the findings straightforward. The pathway has two limbs. The afferent limb carries the signal from the retina to the brainstem along the optic nerve when light is shone into an eye. The efferent limb carries the signal back to both pupils via the oculomotor nerve (cranial nerve III) and the parasympathetic fibres, causing both pupils to constrict. Crucially, light shone into one eye normally causes both pupils to constrict because the signal crosses to supply both sides.

To test the direct reflex, dim the room lights and shine a pen torch into one pupil from the side. The pupil into which the light is shone should constrict. To test the consensual reflex, shine the light into one eye but watch the opposite pupil, which should also constrict. The direct reflex tests the afferent limb of the eye being lit and the efferent limb of that same eye; the consensual reflex tests the afferent limb of the lit eye and the efferent limb of the contralateral eye.

The swinging light test is used to detect a relative afferent pupillary defect (RAPD), also known as a Marcus Gunn pupil. Move the torch rhythmically from one eye to the other, pausing on each. In a normal response, both pupils stay constricted as the light swings across. If there is a defect in the afferent pathway of one eye – for example from optic neuritis, a central retinal artery occlusion or a large retinal detachment – that eye senses less light. When the torch swings onto the affected eye, the reduced afferent signal causes both pupils to paradoxically dilate, because the brain perceives the overall light input has fallen. An RAPD is therefore a sensitive sign of unilateral or asymmetrical optic nerve or retinal disease.

Finally, test the accommodation reflex. Ask the patient to look at a distant point and then quickly switch their gaze to a target held close to their nose. The eyes should converge and the pupils should constrict to bring the near object into focus. The classic abnormality is the Argyll Robertson pupil, which accommodates but does not react to light (‘accommodation-reaction dissociation’), historically associated with neurosyphilis.

Visual Fields

The visual fields are assessed by confrontation, comparing the patient’s field of vision with your own. Sit directly opposite the patient at about one metre, with your eyes level with theirs.

Test each eye separately. Ask the patient to cover one eye, and cover your own opposite eye so that you are mapping their field against yours as a reference. Ask the patient to look straight at your nose, then bring a target (such as a moving fingertip or a red-topped hat pin) in from the periphery in each of the four quadrants, asking the patient to say when they first see it. Their field should match yours if your own fields are normal.

The pattern of any visual field loss localises the lesion along the visual pathway, which is one of the most clinically valuable aspects of the examination:

• A defect in one eye only (a monocular field loss) suggests pathology anterior to the optic chiasm – in that eye, optic nerve or retina.
• A bitemporal hemianopia (loss of the outer half of vision in both eyes) is caused by compression at the optic chiasm, classically by a pituitary tumour.
• A homonymous hemianopia (loss of the same side of the visual field in both eyes) is caused by a lesion behind the chiasm, such as a stroke affecting the optic tract, radiation or occipital cortex.

You should also test for central scotomas (areas of lost vision within the central field) using a red target, as these occur in macular and optic nerve disease, and assess for visual inattention (neglect) by holding both hands in the periphery and wiggling the fingers of one or both at random; a patient who consistently misses one side when both are moved together has visual inattention, typically from a parietal lobe lesion on the opposite side.

The blind spot can also be mapped and compared with your own. The physiological blind spot lies just temporal to central vision and corresponds to the optic disc, where the optic nerve leaves the eye and there are no photoreceptors. With one of the patient’s eyes covered and your opposite eye closed, move a small red target horizontally across the field until it disappears for both of you; an enlarged blind spot suggests optic disc swelling, such as in papilloedema.

Image - Visual field defects mapped to the level of the lesion. A monocular defect localises in front of the chiasm, a bitemporal hemianopia at the chiasm, and a homonymous hemianopia behind it

SimpleMed original

Eye Movements

Eye movements assess the function of the three cranial nerves that supply the extraocular muscles: the oculomotor (III), trochlear (IV) and abducens (VI) nerves.

Ask the patient to keep their head still and follow your finger with their eyes only. Move your finger in an ‘H’ pattern to take the eyes through the full range of horizontal and vertical movement, watching for restriction of movement, misalignment of the two eyes, and nystagmus (involuntary rhythmic oscillation of the eyes). Keep the target far enough away to avoid triggering convergence, and ask the patient to report any pain on eye movement, which is a characteristic feature of optic neuritis.

Throughout, ask the patient to report any double vision (diplopia) and note the direction of gaze in which it is worst, as this helps identify the affected muscle and nerve. The characteristic nerve palsies are:

• Sixth nerve (abducens) palsy – the affected eye cannot abduct (turn outwards), as the lateral rectus is paralysed, producing horizontal diplopia worse on looking to that side.
• Fourth nerve (trochlear) palsy – weakness of the superior oblique causes vertical diplopia that is worst on looking down and in, such as when reading or descending stairs, and the patient may tilt their head to compensate.
• Third nerve (oculomotor) palsy – produces the classic ‘down and out’ eye with ptosis, because the muscles that elevate, adduct and depress the eye are weak. A fixed dilated pupil in this setting is concerning, as it suggests a compressive cause such as a posterior communicating artery aneurysm, which is a surgical emergency.

Screen for a squint (strabismus) first with the corneal light reflex (Hirschberg) test: shine a pen torch towards both eyes and check that the reflection sits in the same, central position on each cornea. A reflex that is off-centre in one eye indicates that eye is misaligned. Then confirm with the cover test: ask the patient to fixate on a target, cover one eye, and watch the uncovered eye – if it moves to take up fixation, a manifest deviation (heterotropia) is present.

Fundoscopy

Fundoscopy (ophthalmoscopy) allows direct examination of the retina, optic disc and retinal vessels. It is best performed in a darkened room; dilating the pupil with a mydriatic such as tropicamide gives a much better view, although in an OSCE you would state your intention to do so and check there is no contraindication first.

Begin by assessing the red reflex from about an arm’s length away, looking through the ophthalmoscope at each pupil. A normal red reflex appears as an even red-orange glow, produced as the ophthalmoscope light bounces off the blood-rich retina at the back of the eye. Absence of the red reflex, or a dark shadow within it, suggests an opacity in the visual axis such as a cataract or vitreous haemorrhage. In children, a white reflex (leukocoria) is a red-flag sign that must prompt urgent referral, as it can indicate retinoblastoma or a congenital cataract.

Then move in close, following a retinal vessel back towards the optic disc. Assess the disc’s colour, margins and central cup. A swollen disc with blurred margins (papilloedema) suggests raised intracranial pressure; a pale disc indicates optic atrophy; and an enlarged, deeply excavated cup is seen in glaucoma.

Examine the retinal vessels and the retinal background, then ask the patient to look directly at the light to bring the macula into view. Important findings include the microaneurysms, dot-and-blot haemorrhages, hard exudates and neovascularisation of diabetic retinopathy; the arteriovenous nipping, flame haemorrhages and cotton-wool spots of hypertensive retinopathy; and the drusen or pigmentary changes of age-related macular degeneration.

Image - A fundus photograph of a normal left eye. The optic disc is seen as the pale circular structure, with the retinal vessels radiating from it and the darker macula to the side

Creative commons source by Mikael Häggström [CC0 1.0 (https://creativecommons.org/publicdomain/zero/1.0)]

Completing the Examination

Thank the patient and wash your hands.

Summarise your findings to the examiner.

To complete the examination, suggest that you would perform a full cranial nerve examination, a slit-lamp examination of the anterior segment, and formal visual field testing (perimetry) and fundus photography as appropriate.

You should also state that you would measure the intraocular pressure if glaucoma is suspected, check a blood pressure and capillary blood glucose / HbA1c given the close link between vision and systemic vascular disease, and refer to ophthalmology for any urgent or unexplained findings.

Quiz

Open SimpleMed+