Strabismus: Adult

Question 0

Ocular alignment depends on an intact afferent input (1), an intact efferent output (2), and normal processing and control centres in the brain.

Answer 0

1. Sight
2. Nerves and extraocular muscles

All causes of strabismus can be considered in this afferent-central-efferent organisation, with hx, ex and ix directed accordingly: afferent (visual loss), central (decompensation of childhood squint; disturbance of processing and control centres); efferent (cranial nerves 3, 4 & 6; NMJ; extraocular muscles).

Question 1

Although there is overlap between childhood and adult strabismus, a practical differentiation is made for which two reasons?

Answer 1

1. Onset AFTER the sensitive period (up to 7-8 years of age) usually causes double vision
2. Adult strabismus is usually caused by disease of the efferent limb of the control of ocular alignment

Question 2

What is the chief symptoms of ‘adult’-onset (after 7-8 years) strabismus?

Answer 2

Double vision: two images seen clearly but separately from each other.

This should be differentiated from blurred vision and from multiple images (caused by cataract). If diplopia is caused by ocular misalignment, it will resolve if either eye is closed. Diplopia can be horizontal, vertical or diagonal depending on the position of the two eyes relative to each other, and will suggest the aetiology.

Question 3

What does squint without double vision suggest?

Answer 3

It implies suppression by the brain of the image from one eye.
This usually occurs in childhood squint, but can also be ‘learned’.

The hx should include questions about general medical problems and symptoms of neurological disease.

Question 4

6 principles of examination in strabismus?

Answer 4

1. First check visual acuity, then verify ocular misalignment.
2. Ocular position (cover test, using corneal light reflex)
3. Ocular movement (lack of movement and maximal double vision in a particular position will suggest the muscle/nerve that is at fault).
4. Ocular examination (esp. important if vision poor - look for opacities, and at the fundus for optic disc swelling/atrophy, retinal disease)
5. Orbital examination (ptosis, lid retraction, lid lag on downgaze).
6. Further examination (as indicated by hx and ex).

Question 5

How does unilateral visual loss (eg. due to cataract or retinal disease) cause strabismus?

Answer 5

It causes the brain to lose afferent feedback in its attempt to control the position of the two eyes.

Question 6

What three signs will a third nerve palsy cause?

Answer 6

Divergence, ptosis and pupil dilation (mydriasis).

?down and out?

Question 7

What are the signs of fourth nerve palsy?

Answer 7

It is difficult to examine for these. Diplopia will be vertical or diagonal, and may be torsional.
Usually, no cause is found: mild head trauma is the most common reason. The prognosis for recovery is good.

Question 8

Two signs of sixth nerve palsy?

Answer 8

1. Eye is convergent
2. Abduction weakness (eye fails to turn laterally).

The prognosis for recovery is good.

Question 9

What are two treatments for myaesthenia gravis?

Answer 9

1. Anticholinesterase inhibitors (eg. pyridostigmine, neostigmine) - increase availability of ACh for functioning muscarinic receptors.
2. Immunosuppresion with steroids and azothioprine may be required.

Question 10

Non-specific orbital inflammation may cause a what?

Answer 10

Myositis.

This may affect extraocular muscles, leading to strabismus.

Question 11

A blow-out fracture of the orbital floor may cause entrapment of orbital tissue around which muscle? When is double vision more likely to occur?

Answer 11

1. Inferior rectus
2. Diplopia more likely to occur with up and down movement than in straight-ahead gaze. Surgery may be needed if diplopia on downgaze persists.

Question 12

Name 6 causes of nerve palsies.

Answer 12

1. Idiopathic: usually spontaneous full recovery
2. Microvascular disease: HTn, diabetes, atherosclerosis - usually spontaneous full recovery.
3. Trauma: even minor head trauma -> fourth nerve palsy.
4. Aneurysm of the PCA: -> third nerve palsy with pain and pupil involvement
5. Inflammation: incl. any cause of vasculitis, sarcoid meningitis, Guillain-Barre syndrome, infections (herpes zoster, syphilis, TB).
6. Neoplasia: benign or malignant, primary or secondary, by compression, usually without evidence of raised ICP.

Question 13

What are the ‘supranuclear’ controls of eye movement?

Answer 13

Coordination of eye movement depends on pathways originating in the cerebral hemispheres, the cerebellum and the vestibular nuclei which travel to the horizontal gaze centre in the pons and to the vertical gaze centre in the midbrain. These are the ‘supranuclear’ controls.
The gaze centres project to the third, fourth and sixth cranial nerve nuclei.

Question 14

Diseases of supranuclear controls are most commonly caused by which three things?

Answer 14

1. Demyelination
2. Ischaemia
3. Haemorrhage

Question 15

What is internuclear ophthalmoplegia, and what are the two signs?

Answer 15

1. Disruption of the medial longitudinal bundle, which connects centres for horizontal movement, results in an internuclear ophthalmoplegia.
2. The two signs are: ipsilateral adduction failure, and nystagmus of the abducting fellow eye.

Internuclear ophthalmoplegia is especially associated with demyelination.