2. Keratoconus
• A degenerative condition that causes the cornea to thin progressively and bulges outwards to form a cone shape.
• This can be treated with glasses and contact lens; ultimately, patient may require keratoplasty

3. Dry eye syndrome
• Dry eye syndrome can occasionally cause diplopia due to uneven tear film
• The diplopia improves with blinking

4. Corneal scarring
• This is usually secondary to corneal trauma or infection and causes corneal haziness
• Topical steroids can be considered but should only be given under specialist supervision

• This causes the lens to become less transparent and as a result incoming light is scattered by the cloudiness of the lens
• Associated symptoms include: blurry vision, light sensitivity, seeing halos, reduction in colour sensitivity and poor night vision

• The diplopia in macular degeneration often presents with “bent” or “warped” images
• There is a reduction in visual acuity (particularly near vision), contrast sensitivity and visual field.
• Photopsia and light glare may also be present

• Diplopia can happen after surgical intervention, such as iridotomy, glaucoma surgery, refractive surgery and scleral buckling surgery
• The diplopia is usually constant
• Dislocated intraocular lens causes diplopia at the lens edge within the visual axis

• Most strabismus is due to abnormal neuromuscular control of eye muscles
• Stroke is the leading cause in adults. Other less common causes include Graves’ disease and trauma.
• Overall, it causes diplopia in adults and amblyopia in children
• Non-paralytic (concomitant) strabismus
  • Children usually present with compensatory head tilt to minimise diplopia
  • Adults often complain of diplopia, alongside a headache and ocular discomfort
• Paralytic (incomitant) strabismus
  • Diplopia is maximal when the patient looks in the direction produced by the weak muscle
• The patient should be referred to an ophthalmologist or neurologist for further investigation and treatment

1. CN III (oculomotor) palsy

• The aetiology of CN III palsy is mainly divided into ischaemic (96%) and compressive (4%)
• The ocular features include:
  • Ptosis – due to paralysis of muscles supporting the upper eyelid
  • “Down and out” gaze at rest – the unopposed activity of superior oblique and lateral rectus
  • Eye movement – unable to elevate, depress or adduct eye
  • Diplopia – not always present as ptosis acts as a barrier to diplopia
  • Pupil
    • Pupil sparing is due to an ischaemic aetiology (and rarely, cavernous sinus syndrome)
    • Fixed and dilated pupil with loss of accommodation is due to a compressive aetiology (could be an indication of posterior communicating artery aneurysm, tumour or pituitary apoplexy)

Patients with non-pupil sparing presentation should be referred urgently for neuro-ophthalmic evaluation (urgent CT and CTA).

2. CN IV (Trochlear) palsy

• CN IV palsy is commonly caused by microvascular damage secondary to diabetes mellitus, hypertension, trauma or demyelinating conditions
• Ocular features:
  • Diplopia – usually vertical and exacerbated by inward and downward gaze
  • Compensatory head tilt – in the direction away from the lesion
  • Ipsilateral hypermetropia
• Fourth cranial nerve palsy secondary to microvascular aetiology usually resolve spontaneously in 4-6 weeks
• Traumatic or congenital aetiology requires an ophthalmology referral so that the patient can be considered for an eye patch, prism or surgical management

3. CN VI (Abducens) palsy

• This is the most common ocular motor palsy in adults as the Abducens nerve (CN VI) has the longest intracranial course of all the cranial nerves
• Common aetiologies include vasculopathy and trauma
• Ocular features:
  • Sudden onset (vascular aetiology) vs progressive onset (compressive aetiology)
  • Diplopia – horizontal and uncrossed, greater at distance than at near
  • Eye movement – inability to abduct eye

• Microvascular aetiology usually resolves within 3 to 6 months
• If an underlying or systemic cause is suspected, treat them primarily

• In Graves’ disease the infiltration of lymphocytes causes oedema of the orbital fat and extraocular muscles
• Ocular features:
  • Diplopia with ptosis, lid retraction and lid lag
  • Painful red eye
  • Incomitant strabismus caused by restricted eye movement (especially on elevation and abduction)

• Myasthenia Gravis is a neuromuscular disease which causes skeletal weakness, including extra-ocular muscles
• Diplopia is intermittent with diurnal variation, tends to be worse towards the end of the day, and improves with rest
• Ptosis is also present

• Multiple sclerosis is an autoimmune demyelinating condition affecting the central nervous system
• Demyelination causes unilateral or bilateral internuclear ophthalmoplegia (INO)
  • The affected eye fails to adduct when attempting to gaze contralaterally (relative to the affected eye)
  • The non-affected eye would demonstrate dissociated horizontal nystagmus on abduction
• Ocular features
  • INO presentation (as above)
  • Saccade (exclusively in the horizontal plane)
  • Upbeat or pendular nystagmus in the primary position
  • Ophthalmalgia
  • Loss of colour vision (especially red desaturation)
  • Light near dissociation
• Visual loss and ocular movement deficit are indications of disease severity