Visual system examination

• Test with Snellen chart (the result is recorded as distance/smallest font size read, e.g. 6/9)
• If the patient wears glasses, do this with glasses on (corrected visual acuity) and off (uncorrected visual acuity)
• A standard Snellen chart is read from 6 metres away but there are smaller versions which may be used at closer distances (e.g. 1 or 3 metres) – adjust the final acuity to ‘1/…’ or ‘3/…’ respectively
• If the patient gets more than two letters wrong, the previous line should be recorded as their acuity. If they get two letters wrong, record acuity as the font size of this line but note ‘-2’ in brackets, e.g. 6/9 (-2); and if they get one letter wrong, note ‘-1’ e.g. 6/9 (-1).

• Read a line of a letter / magazine

• ‘I would also like to test colour vision using Ishihara plates.’

• While the patient keeps both eyes open and focussed on you, hold out your hands in each of their outer visual fields
• Ask them to point at the hand(s) which you are opening/closing. (Inattention to one side = contralateral parietal lesion.)

• Ask the patient to cover one eye with their palm and close your eye on the same side (without using your palm if you can)
• Ask them to stay focussed on your open eye
• Select a white visual fields pin and bring it in from the periphery, keeping it at mid-distance between you and the patient
• Ask them to tell you when they can see it. Move in a diagonal direction into each of the four quadrants.
• Test both eyes individually, comparing their fields with yours
• Pathology:

  • Mononuclear field loss = intra-ocular pathology or ipsilateral optic nerve lesion
  • Bitemporal hemianopia = optic chiasm compression
  • Left/right homonymous hemianopia = contralateral optic tract/radiation lesion, or occipital cortex if macular sparing is present

Offer to test blind spots:

• Ask the patient to cover one eye with their palm and close your eye on the same side (without using your palm if you can)
• Ask them to stay focussed on your open eye
• Hold a red pin mid-distance between you
• Check they can see it as red in the middle (central scotoma = optic nerve lesion)
• Now move the pin horizontally towards the periphery in each direction and to tell you when it disappears
• Map each of their blind spots against your own (large blind spot = papilloedema)

• Ask the patient to focus on a distant object, then hold your finger close to their face and ask them to focus on it
• Pupils should constrict and eyes should converge

• In a dimmed room, ask the patient to hold an open hand between their eyes and focus on a distant point in the room
• Shine the light at each pupil in turn from about 45°
• Observe for direct and consensual papillary constriction
• Defects:

  • Afferent defect (i.e. pupils are symmetrical but when light is shone in affected eye, neither pupil constricts) = CN2 (optic nerve) lesion
  • Efferent defect (affected pupil is persistently dilated, whilst other is reactive to light being shone in either eye) = CN3 lesion 

• Swing the light between the two eyes – the pupil size should stay the same regardless of which eye the light is shone in
• If pupils become more dilated when the light is shone in one eye, then that eye is less sensitive to light and, hence, there is a relative afferent pupillary defect in that eye (partial optic nerve lesion on that side)

Visualised by aiming the ophthalmoscope slightly nasally. Check the 3Cs:

• Cup – normal cup to disc ratio is 0.3 or less, i.e. the cup occupies 3/10 of the diameter of the entire disc (enlarged = glaucoma)
• Colour (grey/pale = optic atrophy)
• Contours (swelling = papilloedema)

Follow the blood vessels out from the optic disc in each direction to visualise each of the four quadrants. Observe for:

• Hypertensive retinopathy signs (silver wiring, AV nipping, cotton wool spots, papilloedema)
• Diabetic retinopathy signs (dot and blot haemorrhages, cotton wool spots, neovascularisation, retinal fibrosis)
• Other characteristic appearances, e.g. drusen (macular degeneration), peripheral pigmentation (retinitis pigmentosa)

Visualise by asking the patient to focus on the light of the ophthalmoscope. Should be pink (dark = macular degeneration).

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