MOVEMENTS OF EYE Physiology Lecture Slideshow

Muscular Movements Of Eye

• Three pairs of muscle
  – Medial and lateral recti
• Move side by side
  – Superior and inferior recti
• Move eyeball up and down
  – Superior and inferior oblique
• Rotate the eyeball

• Nuclei of nerves supplying extraocular are present in brainstem
• Neural connection by medial longitudenal fasiculus
• Cortical control of oculomotor apparatus to occipital lobe
• By
  – Occipitotectal tract– to pretectal area
  – Occipitocollicular tract– to superior colliculus
• Body equilibrium control to oculomotor system(vestibular
  nuclei via medial longitudenal fasiculus)

Fixation Movements

• Eye to fix on a discrete portion of field of vision
  – Involuntary fixation mechanisms
  – Voluntary fixation mechanisms

Voluntary fixation movements

• Voluntary fixation movements are controlled by
  – Bilaterally in premotor field of frontal cortex
• Lesion to the area leads to locking at one point of fixation and
  unable to move to other

• fixation mechanism “lock” on the object of focus– controlled
  by secondary visual areas in the occipital cortex
• located mainly anterior to the primary visual cortex
• Lesion of fixation area is destroyed bilaterally fixation become
  partially or completely

Involuntary fixation movements

• Three types of continuous involuntary movements

1. Continuous tremor (30-80 cycles/sec)
   Caused by successive contractions of motor units in ocular muscles
2. Slow drift of the eyeballs in either direction
3. Sudden flicking movements

• Spot of light fixed on the foveal region of retina
• Tremulous movements move the spot at a rapid rate
• Drifting movements cause slow movement across the cones
• As the image move to the periphery flickering movement
  suddenly brings it back to the center
• Automatic response moves the image back toward the central
  point of vision

Saccidic Movements

• Visual scene is moving requires fixation on every other point in
  visual field
• Jumping of focus from one to the next at a rate of two to three
  jumps per second—saccades
• Movements– opticokinetic movements
• Rapidity of saccades 10% of time is spent in moving the eyes
• 90% of the time being allocated to the fixation sites

Pursuit Movement

• Eyes remain fixed on a moving object—pursuit movement
• Cortical mechanism automatically detects the movement of
  object and develops same change in the eye
• Object is moving up and down in a wavelike form initially eye is
  unable to fixate it within few seconds image perception
  becomes smooth
• High degree of automatic subconscious computational ability
  by the pursuit system for controlling eye movements

Superior Colliculi

• Involuntary fixation mechanism
• Turning the eyes and head toward a visual disturbance

Analysis Of Visual Information

1. The Fast “Position” and “Motion” Pathway
2. The Accurate Color Pathway

• Analysis of Third-Dimensional Position, Gross Form, and Motion
  of Objects
  analyzes
• third-dimensional positions of visual objects in space
  – Overlap with somatic association area
• gross physical form of the visual scene and movement
  – Y ganglion cells but no color
• From primary visual cortex signals move to posterior midtemporal
  area and occipitoparietal cortex.

Analysis of visual color and detail

• Signals from primary visual cortex into secondary visual areas
  of the inferior, ventral, and medial regions of the occipital and
  temporal cortex
• analysis of visual detail and color
• pathway also tells about recognizing letters, reading, texture of
  surfaces,
• Analysis of the information

Analysis of Contrasts in the Visual Image

• Areas of maximum excitation occur along the sharp borders of
  the visual pattern
• Intensity of stimulation is directly proportional to contrast

Analysis of direction in the Visual Image

• Simple Cells – Orientation of Lines and Borders and colors
  – Present in layer IV
• Complex Cells – Line is displaced laterally or vertically in the
  Visual Field
  – Complex contrasts are detected by these cells

Strabismus

• Squint or Cross-eye
• Lack of fusion of the eyes
• Abnormally set patterns of conjugate movements
• Suppression of image from a repressed eye

Amblopia

• Permanent loss of vision with out organic disease in children
  (up to 6 years )
• Strabismus
• Severe refractive errors at birth

Horner Syndrome

• Interruption in sympathetic fibers– cervical sympathetic chain
• Fibers to dilator pupillae are interrupted—constriction of pupil
• Drooping of eyelid– smooth muscles in upperlid, innervated by
  sympathetics
• Blood vessels of corresponding side are dilated
• Sweating doesn’t occur on affected side

Argyll Robertson Pupil

• Final nerve fibers in the pathway through the pretectal area to
  the Edinger-Westphal nucleus –Inhibitory type
• inhibitory effect is lost, the nucleus become active, pupils
  remain constricted, failure to respond to light
• Cause: Syphilis
• Respond to accommodation reflex but not to light reflex

Autonomic Control of Eye

• Parasympathetic Nerves
• Control focusing – Cilary muscles
• Constrict pupil – Sphincter of iris
• Sympathetic Nerves
• Radial fibers of iris – Dilates pupil
  Control of Pupillary Diameter
• Miosis – constriction – 1.5 mm
• Mydriasis – dilation – 8 mm