Pediatrics and Strabismus Vol. 2 Flashcards
Which extraocular muscle has the largest arc of contact?
Inferior oblique (15 mm)
Which extraocular muscles have the smallest arc of contact?
Superior and inferior rectus (6.5 mm)
Which extraocular muscles only have a primary action?
Medial and lateral rectus muscle
What is Sherrington’s law?
Increased innervation and contraction of an extraocular muscle causes decreased innervation and contraction of its antagonist
Which deviation is typically measured to be larger: primary or secondary?
Secondary deviation (Due to increased innervation required to move the restricted eye to fixation)
What is primary deviation?
Amount of misalignment when normal eye is fixating
What is secondary deviation?
Amount of misalignment when restricted eye is fixating
Where does the smooth pursuit pathway start within the brain?
In the striate cortex
Why is there a tonic convergence of the ayes in the normal, resting state?
Because the eyes are divergent in the total paralysis state
Where are the cells responsible for initiation of saccades located?
Within the pontine reticular formation (burst cells)
What does the striate cortex receive input from in the smooth pursuit pathway?
Lateral geniculate bodies
In the smooth pursuit pathway, what nuclei transmit input to the oculomotor nuclei?
Vestibular nuclei
What is the primary thalamic nucleus connecting the retina and striate cortex?
Lateral geniculate body
What Brodmann area is associated with the primary visual cortex?
Brodmann area 17
Where do approximately 90% of the retinal ganglion cells terminate?
Lateral geniculate body (LGN)
What are M neurons particularly responsive to?
Moving objects
What are the two primary neural systems of the retinogeniculocortical pathway?
Magnocellular (M) and parvocellular (P)
Where does the magnocellular system (M) originate?
Parasol retinal ganglion cells
Where does the parvocellular system (P) originate?
Midget ganglion cells
What neural system accounts for approximately 80% of retinal input?
Parvocellular system (P)
What is the primary function of the parvocellular system (P) system?
Object detail (color, shape, depth,etc.)
Where does the koniocellular system (K) originate?
Bistratified ganglion cells
What is the primary function of the koniocellullar system (K)?
Color vision (especially blue)
Which layers of the LGB are parvocellular? Magnocellular?
1 to 4 (P), 5 to 6 (M)
What layers of the LGB receive input from the contralateral nasal retina?
1, 4, and 6
Which layers of the LGB receive input from the ipsilateral temporal retina?
2, 3, and 5
During gestation, when does maximal ganglion retinal cell count occur?
Week 18
When does retinal ganglion call loss begin to occur during gestation?
Week 30 (occurs until first few months of life after birth)
What is normal estimated visual acuity at birth?
20/400
Where is the primary site of amblyopia thought to be located?
Primary visual cortex
