The eye consists of 3 layers
I. corneoscleral layer: outside layer
  1. anterior part is the cornea (the transparent part)

  2. sclera is the remaining portion (developed from meninges)
 

II. uvea
  1. choroid: most posterior part (developed from meninges)

  2. ciliary body: in the middle

    A. ciliary body has 2 layers

    B. suspensory ligaments: attaches this to the lens
 
  3.  iris: most anterior part

    A. the iris divides the area between the cornea & lens into 2 chambers both
         of which are filled with aqueous humor
      a. chambers: (1) anterior chamber (2 ) posterior chamber
      b. aqueous humor drains thru the canal of Schlemm

    B. composed of 2 layers

    C. two muscles in the iris control pupil size
 

III. retina
  1. the retina is divided into 3 regions
    A. retina proper: posterior part where photoreceptors are
    B. inside layer of the ciliary body (connected to retina proper by ora serrata)
    C. inside layer of the iris: the most anterior region

  2. the retina also has 2 layers (an inner & outer layer)

  3. Papilla (optic disk): where the optic nerve enters the retina
 

The lens separates the front & back portion of the eye

I. Lens: this like the cornea should be transparent
 1. aqueous humor in front of the lens

 2. vitreous humor & vitreous body (jellylike stuff) behind the lens

   A. zonal fibers attach the lens to the ciliary body
     a. accommodation:
     b. presbyopia

 3. cataract: when the lens becomes opaque

 4. along with the cornea the lens provides and a refractive element

 5. why might a person need eye glasses
   A. presbyopia

   B. an elongated eye: the image falls in front of the retina (myopia)

   C. a flattened eye: the image falls behind the retina (hyeropia)

   D. spherical aberrations of the cornea: e.g., astigmatism
 

I. photoreceptors: the second (from the inside) of the 10 layers

 1.  Cones: are responsible for color vision.
 

 2. Rods: they are most sensitive to light
 

II. Bipolar cells no action potentials occur in bipolar cells
 

III. ganglion cells: action potentials first occur here

 1. The axons of the ganglion cells make up the optic nerve

  A. they penetrate the sclera at the optic disk (papilla)
    a. a blind spot (scotoma)

    b. papilledema: a swelling that occurs with intracranial pressure
 

IV. interneurons on the retina: they distribute information laterally
 1. horizontal cells:

 2. amacrine cells:
 

V. The special neural wiring of the eye
 1. convergence: ganglion cells receive input from many photoreceptors.
  A. interneurons are responsible for convergence

 2. lateral inhibition: the response of one retinal cell can inhibit other retinal
     cells.

 3. receptive field: this is the part of the retina and the corresponding part of
     the visual world to which the ganglion cell responds.

  A. Most ganglion cells have a center-surround receptive field:

  B. There are also on/off ganglion cells which respond when a light goes on
       when it goes off.

I. the main pathway
 1. The optic nerve joins at the base of the brain to form the optic chiasm:

 2. at the chiasm, information (axons) from ganglion cells serving the nasal
     side cross

 3. The LGN contains 6 layers
  A. magnocellular layers:
  B. parvocellular layers:

 4. Each LGN then projects to the ipsilateral primary visual cortex

  A. optic radiations: axons from LGN to the visual cortex
 
  B. each cortical hemisphere receives information from the contralateral half
       of the visual scene
 

II. subpathways include:
 1.  suprachiasmatic nucleus: controls internal clock
 2.  accessory optic N: coordinates eye movements with head movements
 3.  pretectum: controls pupil size & lens accommodation,
 4.  superior colliculus: which controls eye movements
 

I. The visual (striate) cortex:
 1. The striate cortex consist of 6 layers that are arranged in parallel bands.

 2. Some cells respond best when each eye sees a stimulus in a slightly
     different location (retinal disparity)

 3. simple cells: cells of the striate cortex that are sensitive to the orientation
     of lines  (Kingsley p.456)

 4. complex cells: have a larger receptive fields
   A. they respond to moving lines of a particular orientation
       (Kingsley p.458)

 5. The visual cortex has a columnar organization (Kingsley 459)

     a. e.g., one column may contain cells that respond to horizontal lines

   A. hypercolumn: a set of orientation columns for each eye
 

II. Visual Association Cortex
 
 1. just outside the striate cortex lies the extrastriate cortex (or prestriate or
     circumstriate cortex)

 2. The visual association cortex contain 2 streams of analysis, but both
      begin in the striate cortex

  A. parvocellular pathway (ventral stream) turns downward ending in the
       inferior temporal lobe

  B. magnocellular pathway (dorsal stream) turns upward ending in the
       cortex of the posterior parietal lobe

3. color constancy (seeing the same color under different lighting conditions)
  A. achromatopsia (vision without color)

4. The recognition of patterns occurs at the end of the ventral stream

5. Damage to the association cortex can cause a visual agnosia (can not
    recognize common objects by sight)
  A. apperceptive agnosia: they can not recognize objects by their shape
    a. prosopagnosia here you can not recognize faces (even your own).

  B. associative agnosia: here a person can not name what they see.

6. some cells responds best to moving stimuli going in a particular direction
    regardless of shape or size (input from the superior colliculus)
  A. movement agnosia (Kingsley p. 462)

7. The parietal lobe appears to be involved in perceiving & remembering the
    location of objects & possibly guide actions.

  A. Balint’s syndrome
     a. optic ataxia:
     b. ocular apraxia:
     c. simultanagnosia:
     d. elements of neglect have been noted

8. our capacity to perceive visual stimuli depends on early environmental
    stimulation

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