Examination of the eyes and vision frequently appears in OSCEs. You’ll be expected to pick up the relevant clinical signs using your examination skills. This guide provides a step-by-step approach to examining the eyes, assessing vision and performing fundoscopy. It also includes a video demonstration.
Wash your hands
Confirm the patient’s details (name and date of birth)
Explain the examination
Appropriately position the patient
- Snellen chart
- Ishihara chart
- Fine print reading chart
- Pen torch
- Mydriatic eye drops
Decreased visual acuity has many potential causes:
- Refractive errors
- Ocular media opacities such as cataract or corneal scarring
- Retinal diseases such as age-related macular degeneration
- Optic nerve (CN II) pathology such as optic neuritis
- Lesions higher in the visual pathways
Optic nerve (CN II) pathology usually causes a decrease in acuity in the affected eye. In comparison, papilloedema (optic disc swelling from raised intracranial pressure), does not usually affect visual acuity until it is at a late stage.
Assessment of visual acuity
1. Stand the patient at 6 metres from the Snellen chart.
2. If the patient normally uses distance glasses, ensure these are worn for the assessment.
3. Ask the patient to cover one eye and read the lowest line they are able to.
4. Visual acuity is recorded as chart distance (numerator) over the number of the lowest line read (denominator).
5. Record the lowest line the patient was able to read (e.g. 6/6 which is equivalent to 20/20).
6. If the patient reads the 6/6 line, but gets 2 letters incorrect, you would record as 6/6 (-2).
7. If the patient gets more than 2 letters wrong, then the previous line should be recorded as their acuity.
8. You can have the patient read through a pinhole to see if this improves vision (if vision is improved with a pinhole, it suggests there is a refractive component to the patient’s poor vision).
9. When recording the vision it should state whether this vision was unaided (UA), with glasses or with pinhole (PH).
10. Repeat the above steps with the other eye.
If the patient is unable to read the top line at 6 metres (even with pinhole) move through the following steps as necessary:
1. Reduce the distance to 3 metres from the Snellen chart (the acuity would then be recorded as 3/denominator).
2. Reduce the distance to 1 metre from the Snellen chart (1/denominator).
3. Assess if they can count the number of fingers you’re holding up (recorded as “Counting Fingers” or “CF”).
4. Assess if they can see gross hand movements (recorded as “Hand Movements” or “HM”).
5. Assess if they can detect light from a pen torch shone into each eye (“Perception of Light”/”PL” or “No Perception of Light”/”NPL”).
Fine print reading
1. Ask the patient to cover one eye.
2. Ask the patient to read a paragraph of small print in a book or newspaper.
3. Repeat assessment on the other eye.
If the patient normally wears glasses for reading, ensure these are worn for the assessment.
Colour vision assessment
1. Ask the patient to cover one of their eyes.
2. Ask the patient to read the numbers on the Ishihara plates. The first page is usually the ‘test plate’ which does not test colour vision and instead assesses contrast sensitivity. If the patient is unable to read the test plate, you should document this. If the patient is able to read the test plate, you should move through all of the Ishihara plates, asking the patient to identify the number on each. Once the test is complete, you should document the number of plates the patient identified correctly, including the test plate (e.g. 13/13).
3. Repeat the assessment on the other eye.
If the patient normally wears glasses for reading, ensure these are worn for the assessment.
1. Sit directly opposite the patient, at a distance of around 1 metre.
2. Ask the patient to cover one eye with their hand.
3. If the patient covers their right eye, you should cover your left eye (mirror the patient).
4. Ask the patient to focus on your face and not move their head or eyes during the assessment. You should do the same and focus your gaze on the patient’s face.
5. As a screen for central visual field loss or distortion, ask the patient if any part of your face is missing or distorted. A formal assessment can be completed with an Amsler chart.
6. Using a red hat pin (or alternatively, a cotton bud stained with fluorescein/pen with a red base) start by identifying and assessing the patient’s blind spot in comparison to the size of your own. The blind spot is found just temporal to central vision at eye level. An enlarged blind spot can be a sign of a swollen optic disc.
7. Assess the peripheral visual field by comparing to your own and using the red hat pin. Start from the periphery and move the target towards the centre until the patient can see it. If you are able to see the red hat pin but the patient cannot, this would suggest a reduced visual field.
8. Repeat this process for each quadrant, then repeat the entire process for the other eye.
9. Document your findings. The left eye should be documented on the left side of the page and the right eye on the right.
- Normal size varies between individuals and depends on lighting conditions (i.e. smaller in bright light, larger in the dark).
- Pupils are usually smaller in infancy and larger in adolescence.
- Pupils should be round, abnormal shapes can be congenital or due to pathology (e.g. posterior synechiae seen in uveitis, post-surgery).
- Note any asymmetry between the pupils (anisocoria). This may be longstanding and non-pathological, but may relate to pathology. If more pronounced in light this would suggest that the larger pupil is the abnormal pupil, if more pronounced in dark this would suggest the smaller pupil is abnormal.
- Examples of asymmetry include a large and fixed pupil in CN III palsy and a small and reactive pupil in Horner’s syndrome.
Inspect for ptosis
- Ptosis can be a sign of Horner’s syndrome/CN III palsy.
To best see pupillary reflexes the room should be dimly lit.
Direct pupillary reflex
- Shine a light into the pupil and observe constriction of that pupil.
- Sluggish reaction or lack of constriction may suggest pathology (optic nerve/brain stem/drugs).
Consensual pupillary reflex
- Again, shine a light into the pupil, but this time observe the contralateral pupil.
- A normal consensual response involves the contralateral pupil constricting.
Lack of a normal consensual response may suggest:
- Damage to one or both optic nerves
- Damage to the Edinger-Westphal nucleus
Swinging light test
1. Move the pen torch rapidly between the two pupils.
This test can detect a relative afferent pupillary defect (RAPD), which presents with paradoxical dilatation of the affected pupil when light is shone into it (this abnormal sign is also known as a “Marcus-Gunn pupil”). A RAPD is caused by damage to the afferent pathway of the optic nerve on the side of the abnormal pupillary response (e.g. multiple sclerosis, advanced glaucoma).
1. Ask the patient to focus on a distant object (clock on the wall/light switch).
2. Place your finger approximately 20-30cm in front of the eyes (alternatively, use the patient’s own thumb).
3. Ask the patient to switch from looking at the distant object to the nearby finger/thumb.
4. Observe the pupils, you should see constriction and convergence bilaterally.
1. Ask the patient to focus on a target, whilst you shine a pen torch towards both eyes. This will reveal the corneal reflex on each eye, which should be located in the centre of the pupil if no ocular deviation is present.
2. Ask the patient if they see one or multiple light sources. If the patient reports seeing more than one light source, ask the patient how they are positioned (e.g. side by side or one above the other). Determine whether the diplopia is monocular or binocular by seeing if the double vision disappears when one eye is occluded (binocular diplopia is only present when both eyes are open).
3. Cover one of the patient’s eyes.
4. Observe the uncovered eye for movement:
- No movement = normal response
- Eye moves temporally = convergent squint (esotropia)
- Eye moves nasally = divergent squint (exotropia)
5. Repeat the cover test on the other eye.
1. Hold your finger about 30cm directly in front of the patient’s eyes and ask them to look at it. Look at the eyes in the primary position for any deviation or abnormal movements.
2. Ask the patient to keep their head still whilst following your finger with their eyes. Also ask them to let you know if they experience any double vision.
3. Move your finger through the various axes of eye movement (“H” shape).
4. Observe for restriction of eye movement and note any nystagmus.
1. Darken the room (this is essential).
2. The patient should ideally have their pupils dilated with short-acting mydriatic eye drops such as tropicamide 1%. Advise the patient they will be unable to drive for a period of time if they are given dilating drops. You will be unable to monitor pupil reactions once dilating drops have been applied, furthermore assessing vision, colour vision, double vision and visual fields will be less accurate once drops are instilled.
3. Ask the patient to fixate on a distant object.
4. First, assess the anterior segment of the eye using the ophthalmoscope. Fluorescein dye can be applied as an eye drop which will stain and fluoresce yellow under the blue cobalt light filter of the ophthalmoscope if there is damage to the corneal or conjunctival epithelium (e.g. an abrasion). Look for white opacities on the cornea which may be suggestive of a corneal ulcer.
Assess red reflexes
1. Ideally, this should be assessed at a distance of around 30cm.
2. Looking through the ophthalmoscope, observe for a reddish/orange reflection in each pupil.
The red reflex is caused by light reflecting back from the vascularised retina.
Absence of the red reflex in adults is often due to cataracts in the patient’s lens blocking the light. Patients may have a white reflex (leukocoria) and in children this may be a sign of retinoblastoma or retinal detachment.
Move in closer and examine the eye with the ophthalmoscope
1. Move in closer whilst maintaining the red reflex and examine the retina with the ophthalmoscope. You may need to change the focus wheel to account for the difference in glasses prescription between the patient and yourself. Approach from an angle slightly temporal to the patient.
2. Begin by identifying a blood vessel and then follow the branching of this blood vessel towards the optic disc (the branches point like arrows towards the optic disc).
3. Assess the optic disc (colour/margin/cupping).
4. Assess the retinal vessels for pathology (e.g. arteriovenous nipping/neovascularization/haemorrhages).
5. Finally, assess the macula by asking the patient to look directly into the light:
- Drusen are typically noted in macular degeneration
- A cherry red spot is typically noted in central retinal artery occlusion
To complete the examination
Thank the patient
Wash your hands
Summarise your findings
Suggest further assessment and investigations:
- Amsler chart – useful if macular degeneration is suspected
- Retinal photography
- Full cranial nerve examination