Lecture 02 - Vision 1 Flashcards
Cornea and sclera
cornea = super organized, distinct planes = clear
sclera = disorganized, randomly oriented= opaque
-though, thick, inelastic collagen, outer wall of eye
Anterior chamber (aqueous humour)
between cornea and iris
- clear, watery aqueous humor
- measure this for dilation
Iris
vascular muscular diaphragm
- pupil: central opening
- diameter of pupil under neural control (PS, Symp)
Lens
proteins (collagen) assembled to be optically clear and flexible
-lens epithelial cells organized front to back organization because size limited
Ciliary body
- connects lens to scleral wall
- muscle and secretory epithelium
- neural control of ciliary muscle affects shape of lens, independent of iris/pupil
- lens capsule is under constant pull from ciliary muscle
- relax muscle, lens naturally curl up and change shape –> accomodation
Vitreous Chamber/cavity
optically empty gel of hyaluronic acid molecules
-physically supports retina layer to remain in place against scleral wall
Retina and Choroid
Neural and vascular layers lining inside of scleral wall
-minimize blood structures blocking vision
Optic Nerve
collection of retinal nerve cell axons transmitting info to Lateral Geniculate Body via optive nerve –> optic chiasm –> optic tract –> lateral geniculate body
- outer sheath is contiguous with CNS dura mater
- get myeline so light passage isn’t disturbed
- ganglion cell bodies in retina, axons travel to common exit area and gather into cylinder
Hyaloid Canal
Remnant of embryology
-eye starts as tube and develops into sphere
-canal is not visible clinically
(potential structure, not anatomic)
Principles of Refraction
At interface of two materials of different optical densities, light bends towards the perpendicular of the surface of the interface
-affect bending by changing curvature of the interface or changing optical densities
- **surface of cornea is more important for light focusing because of the curvature than lens
- largest refraction at air:tear interface
Function of the lens
refraction/focusing of image by accomodation
- change lens shape to focus on distant or near images (changing focal distance)
- relaxing ciliary muscle –> lens become more round
Accomodation
lens capsule is elastic
-totally relaxed state of lens = round
-ciliary muscle contracts to allow the lens to be more round
- Parasymp:
edinger-westphal –> CN3 –> ciliary ganglion (in eye socket) ***synapse –> ciliary nerve –> ciliary muscle
Pulillary Aperture
pupil size important variable in vision
- adapt to amount of ambient light
- smaller pupil = increased depth field = “pinhole effect”
- pinhole minimizes blur of other light rays coming in
- distinguishes between lens refraction angle issues from other issues like optic nerve/retina problems
Structure of Pupil
Constrictor
- pupil margin = circular muscle (sphincter pupillae)
- parasymp control (ACh, pilocarpine
- edinger-westphal –> CN3 –> ciliary ganglion –> ciliary nerve –> sphincter
Dilator
- within stroma of pupil = radial muscle (dilator pupillae)
- symp control (epinephrine, congeners)
- pharmacologically parasymp antagonists = dilation (drops for dilation)
- lateral horn –> superior cervical ganglion –> ciliary nerve –> dilator
Retinal cell types
4 types of cells
- Retinal pigment epithelium - support photoreceptors, absorb light and heat (lots of blood, garbage trucks for 2)
- Rods and cones - change light energy to synaptic energy (physical to chemical)
- Interneurons - relay, process, modify image signals WITHIN RETINA
- Ganglion cells - relay, process, modify image signals TO BRAIN (brain can’t interpret if these are lesioned)
photoreceptors
convert photons into neural information
interneurons & ganglion cells
process and transmit neural info
retinal pigment epithelium
support metabolic needs of photoreceptors
heat sink
absorb unprocessed photons
Rods
Rods are sensitive (function even in low light)
“white” only - no color perception
great numbers in retinal periphery (image locator)
none in center
wide connections to interneurons - 1000 rods to 1 ganglion
allows sensitivity
Cones
insensitive: require much ambient light
color vision (RBG)
greater number in central retina (macula) to give detail and locater analyze function (image resolution)
none in peripheral retina
very narrow connections to interneurons (often 1:1)
allows detail
cell bodies form foveal pit
different cones combine to get different colors
Foveal Pit
Mostly cones - RBG analyzer
- age related macular degeneration = color degen
- forms dark circle in the eye because absorbing color, not bouncing light off on the way
- curved fibers
Central visual pathways
visual fields
retinal projections
visual cortex
Visual fields
receptive areas of retinal cells
- geographically organized –> lateral geniculate body
- split from Right/Left eye into Right/Left fields of vision
- right field, left field overlap = true binocular vision
- right fields and left fields become joined/overlaid at optic chiasm
Retinal projections
lateral geniculate = synapse
segregation/retinotopy - right/left and upper/lower
