Strabismus Flashcards
What is binocular single vision?
Two images from two eyes combine to form one central image
What is Stereopsis?
3D depth perception
Which is greater? Binocular acuity or monocular acuity?
Binocular acuity
What is the importance of Stereopsis and Binocular single vision?
1) Increase field of vision
2) Eliminate the blind spot
3) Depth perception
4) Estimation of distance
Binocular eye movements are called __.
Versions
Monocular eye movements with the other eye covered are called __.
Ductions
What are the 6 muscles of the eye?
1) Medial Rectus
2) Lateral Rectus
3) Superior Rectus
4) Inferior Rectus
5) Superior Oblique
6) Inferior Oblique
Which muscles of the eye does the third cranial nerve (Oculomotor) supply?
1) Medial Rectus
2) Superior Rectus
3) Inferior Rectus
4) Inferior Oblique
Which muscle of the eye does the fourth cranial nerve (Trochlear) supply?
Superior Oblique
Which muscle of the eye does the fifth cranial nerve (Trigeminal) supply?
Lateral Rectus
The total number of the positions of gaze is _.
9
What are Yoke muscles?
A pair of muscles (one muscle in each eye) moving the eye to the same direction of gaze
What is squint (strabismus)?
Misaligned eyes (both eyes are not looking in the same direction)
What is concomitant (non-paralytic) squint?
The angle of deviation is not affected by the direction of gaze. (Eye muscles all move normally)
What causes concomitant (non-paralytic) squint?
UNCLEAR IMAGES AS A RESULT OF:
1) Refractive error
2) Opacities in the media of eye
3) Abnormalities of the retina that prevent the translation of a correctly formed image into neural impulses
Is concomitant (non-paralytic) squint congenital or acquired?
Congenital
Is non-concomitant (paralytic) squint congenital or acquired?
Acquired
When is diplopia at its peak in non-concomitant (paralytic) squint?
When attempting to look in
the direction requiring the action of the weak muscle.
What is non-concomitant (paralytic) squint?
The degree of misalignment varies with direction of the gaze (An eye muscle is not functioning properly)
Non-concomitant (paralytic) squint may indicate:
1) A nerve palsy
2) An extra-ocular muscle disease
Which nerve palsies may cause non-concomitant (paralytic) squint?
1) 6th nerve (Abducens)
2) 4th nerve (Trochlear)
3) 3rd nerve (Oculomotor)
What does a 6th nerve palsy cause?
Failure of Abduction
What does a 4th nerve palsy cause?
Defective depression of the eye when in adduction
What does a 3rd nerve palsy cause?
1) Failure of adduction, elevation and depression of the eye
2) Ptosis
3) Dilated pupil
What causes dysthyroid eye disease?
Infiltration of the extraocular muscles with lymphocytes and the depositions of glycosaminoglycans
Which muscle is most commonly affect in dysthyroid eye disease?
Inferior rectus
What are the complications of dysthyroid eye disease?
1) Chemosis & corneal ulcers = corneal perforations
2) Compressive optic neuropathy = blindness
Management of dysthyroid eye disease?
1) Systemic steroids
2) Radiotherapy
3) Surgical orbital decompression
4) Prisms
How do you diagnose myasthenia gravis?
Edrophonium test
How do you treat myasthenia gravis?
1) Neostigmine (acetylcholine esterase inhibitor)
2) Thymectomy
What is ocular myositis?
Inflammation of the extraocular muscles
Signs and symptoms of ocular myositis?
1) Pain
2) Diplopia
3) Restriction of movement
Mode of inheritance of Ocular Myopathy?
Mitochondrial DNA mutation
Describe the eye movement in ocular myopathy?
Slowly and symmetrically
reduced