Approach to diplopia

Question 1

Diplopia is the perception of 2 separate images when viewing a single object

The image may be displaced horizontally, vertically, oblique/angulated or mixed relative to true image

This can be due to ophthalmological or neurological cause.

Question 2

Neurolocalisation of diplopia

Answer 2

A. Binocular or monocular?
- Step: cover each eye one at a time, does the double image persist or resolved?

1. Monocular: persist on covering the other eye -> Ophthalmologic
   - Refractive error, corneal disorder, cataracts, iris injury, retinal detachment, macular disorder
2. Binocular: resolves on covering either eye (misaligned axis) -> Neurologic
   - Muscles: CPEO, restrictive eye diseases (thyroid eye disease, muscle entrapment)
   - NMJ: myasthenia gravis
   - Cranial neuropathy: idiopathic, Miller Fisher
   - Brainstem: cranial nuclei and gaze centres (INO, 1 and half syndrome)
3. Bilateral monocular diplopia: double vision persist regardless of which eye
   - Bilateral ophthalmologic abnormalities
   - Visual cortex disorder: palinopsia, cerebral polyopia

B. Direction of greatest misalignment -(horizontal/vertical)
- Step: which direction does the diplopia get worse? (H-test)
- Step: is the diplopia worse on near or far vision (near-far test)
- Step:

1. Binocular horizontal diplopia - MR (CN3) or LR (CN6) defect
   - Worsens on near vision: MR weakness (vergence defect) (excluding INO - sparing of convergence)
   - Worsens on looking far: LR weakness
2. Binocular vertical diplopia - supraductors/infraductors defect

Supraductors: SR (CN3) and IO (CN3)
- Abducted upward: SR ; adducted upwards: IO
Infraductors: IR (CN3) and SO (CN4)
- Abducted downward: IR; adducted downwards: SO
Cyclotorsion: SO (incyclo) and IO (excyclo)

C. Accompanying signs
1. Fatigability: myasthenia gravis
2. Multi-CNs without long tract sign: cranial nerve syndromes
3. Multi-CNs with long tract signs: Brainstem syndromes

Question 3

Examination of diplopia

Answer 3

A. Inspection
- Abnormal head posturing
- Misalignment of eyes
- Ptosis
- Facial weakness
- Speech
- Feeding tube (swallowing difficulty)
- Hemiparesis

B. Manoeuvers
1. Hirschberg test (poor sensitivity - 7 degree deviation causes 1mm shift of light reflection)
- Shine light at eyes and observe light reflection off cornea
(Normal: reflection within 0.5mm nasally from midline of pupil)

2. Cover-uncover test
   - Cover 1 eye, observe uncovered eye shift in fixation
   - Remove cover and observe refixation movement

C. EOM movement
1. H test with smooth pursuit
2. Horizontal and vertical saccades - assess initiation, speed, range of movement, accuracy
(If ocular misalignment is subtle, occlude each eye and examine individually)

D. Park-Bielschowsky test for vertical diplopia
(applies principles of supra/infraductors, cyclotorsion)
1. Observe eyes position at primary gaze
- Any eyes higher than the other?
2. Look to left and right
- Which direction of worsening misalignment?
3. Roll head to left and right
- Which direction of worsening misalignment?