Strabismus Flashcards
What are antagonist-agonist muscles?
Muscles in the same eye that move the eye in different directions. For example, left MR (adduction) and left LR (abduction)
What are synergist muscles?
Muscles in the same eye that move that eye in the same direction. For example, right IR (depression) and right SO (depression)
What are Yolk muscles?
Muscles, one in each eye, that cause the two eyes to move in the same direction
For example, the right LR and the left MR are responsible for right gaze, and hence they are termed yolk muscles
What is Hering’s law?
States that yolk muscles involved in a particular direction of gaze receive equal
and simultaneous flow of innervations. For example, contraction of the MR is accompanied by equal contraction of the contralateral LR
What is Sherington’s law?
States that an increase in innervation of a muscle is accompanied by a decrease
in innervation of its antagonist. For example, when the left LR contracts, the left MR relaxes
What is Amblyopia?
Amblyopia is characterized by a reduction in VA in the early years of life (<8 years of age) due to a developmental failure of the visual pathway between the eye and the visual cortex in the occipital lobe. It is usually unilateral and is caused by
abnormal stimulation due to various aetiologies.
- Aetiologies: Strabismus, refractive error and stimulus deprivation (e.g. cataract)
Management of Amblyopia?
- Treat underlying cause.
- Occlusion therapy: The good eye is patched to allow visual connections
between the amblyopic eye and the brain to develop properly. - Pharmacologic penalisation of the good eye using atropine
What is binocular single vision?
Ability to fuse images from both eyes to produce a single image. Characteristics
of binocular vision are as follows
Sensory fusion
Motor fusion
Stereopsis: perception of depth
Tests for binocular status?
- Simultaneous perception and fusion
● Worth 4-dot test, Bagolini glasses and synoptophore. - Motor fusion
● Base-out or base-in prism bar or Risley prism tests. Applying a base-out prism moves the image to the temporal retina so the eye has to converge to achieve binocular single vision. The opposite is true for a base-in prism. - Stereopsis
● Titmus, Lang, TNO, Frisby and synoptophore
What is Heterophoria?
Deviation of the eye that is hidden by fusion and revealed when fusion is broken,
for example, with an alternating cover test
Two types:
Esophoria: Inward deviation of eye
Exophoria: Outward deviation of eye
What is heterotropia?
Abnormal alignment of the eye, also known as a manifest squint. Can be tested
using the cover test.
● Esotropia: Convergent squint
● Exotropia: Divergent squint
What is accommodative esotropia?
Accommodative esotropia is due to refractive errors or convergence excess. It
usually presents in patients between 1 and 5 years old and is associated with hypermetropia
What is non-accommodative esotropia?
Infantile esotropia develops within the first 6 months of life and is the most
common esotropia. Other types of non-accommodative esotropias exist and
usually present after the first 6 months of life.
Two types of exotropia?
Intermittent exotropia - split into distance and near
Constant exotropia
What is microtropia?
A small angle squint <10PD (5°), most commonly an esotropia associated with
anisometropia. Patients have subnormal binocular single vision with sensory
and motor fusion and reduced stereopsis.
