- Electromagnetic Energy
- Light
- Frequency
- How often it comes
- Wave length
- Peak to peak
- Long length is slow
- Color
- Amplitude
- How tall wave
- Intensity: brightness
- Absorb & Reflect
- Light sources:
- sun, light bulb, candle, moon
- Reflection based on:
- Relative distance
- Object color & smoothness
- Perceived color is reflected
- Everything but purple absorbed
- Light sources:
- Eye
- Transducer of light into neural signal
- Sclera
- Greek for hard
- 1 mm thick
- Fibrous strands in parallel; like fiber strapping tape
- White of the eye
- Covers entire ball
- Not cornea & optic nerve exit
- Fibers resist internal pressure
- twice the atmosphere
- Muscles
- Held-moved by 6 tiny muscles
- Nystagmus = can’t hold eyes still
- Strabismu (strabismic amblyopia)
- Lazy Eye or Amblyopia
- Eyes don’t point same direction
- Two don’t help perceive depth
- Treatment
- Patch over active eye
- Play action video games
- Cornea
- Bulges out from sclera
- Smooth, neatly organized
- Transparent (no blood vessels)
- Very sensitive to touch (close lid)
- Nourished by tears (on outside)
- aqueous humor (on inside)
- 2/3 of focus of eye
- Dome-shaped
- Irregularity of surface
- Astigmatism = blurry lines
- Astigmatism Symptoms
- squinting & blurred vision
- headaches, eye strain
- Cornea warping
- Blurred vision for lines in one direction
- Treatment
- Glasses before age 3-4 years
- Irregularity of surface
- Aqueous Humor
- Spongy tissue
- Keeps eye inflated
- Removes waste
- Mostly water
- Also an antioxidant
- Protects from UV rays
- Provides oxygen, nourishment to cornea & lens
- Continuously refreshed
- In from ciliary body
- Drained into Schlemm’s canal
- Glaucoma
- Blockage of aqueous humor
- Damage to iris
- Blindness
- Iris
- 2 layers
- Outer layer of pigment
- Color part of eye
- Can be translucent (albinos)
- Inner layer of blood vessels
- Pupil of the Iris
- Hole in middle of iris
- 2 sets of muscles
- circular = close pupil
- radial = open pupil
- Varies in size (4:1 ratio)
- Allows 16: 1 ratio of light
- actual ratio changes with age
- in dim light, 80 yr old has half as wide opening as 20 yr old
- Advantages of small opening = depth of field
- Allows 16: 1 ratio of light
- Lens
- Held in place by strings (zonules)
- Suspended
- Crystalline (clear crystal-like proteins)
- Bean shaped
- Diameter & thick of large aspirin
- Has no blood vessels
- Mostly water & protein
- 3 parts
- elastic covering
- changes shape of lens
- controls flow of aqueous humor
- epithelial
- toward edge of lens
- synthesizes proteins
- lens
- Never stops growing
- Adds fibers to edge
- center becomes thin
- some center fibers there at birth
- elastic covering
- As ages
- more dense & hard (sclerosis)
- less transparent (cataract)
- Can be irregularly shaped
- Can cause astigmatism, but not common
- Cataracts
- Born with cloudy lens
- If surgically repaired
- at 2-6 months old
- eventually nearly normal vision
- Early cataract in left eye
- limits visual info to right hem.
- face recognition
- Vitreous Humor
- Jelly-like, like raw egg whites
- Not continuously renewed
- Floaters
- More liquid with age
- Can become detached
- posterior vitreous detachmentor (PVD)
- Retinal Circulatory System
- 1 of 2 blood supplies
- in front of the retina
- leaves shadows on retina; brain ignores
- steady state information
- Supplies nourishment to non-receptor structures
- (ganglion, horizontal cells, etc.)
- 1 of 2 blood supplies
- Retina
- Inner limiting membrane
- Vitreous humor & retina
- Formed by astrocytes
- Feet of Müller cells: inner limiting membrane
- Müller cells (glia): support cells for retina
- Act as light collectors
- Like a fiber optic plate
- Funnels light to rods & cones
- Inner limiting membrane
- Macula
- Depression in retina
- Unobstructed
- Near center
- Off to side
- Macular Degeneration
- Dry (nonexudative)
- Cellular debris (drusen)
- Yellow deposits grow between retina & choroid
- Drusen deposits grow, retina becomes detached
- Severity depends on size and # of drusen
- Wet (exudative)
- Choroid blood vessels grow
- Retina becomes detached
- Blood vessels from choroid (blood system)
- More severe
- Treatments
- Laser coagulation and meds
- Older adults (major cause of blindness)
- Loss of vision in center
- Can’t read or recognize faces
- Lose most detail of images
- Dry (nonexudative)
- Fovea
- Also called fovea centralis
- In center of macula
- Fine details & sharp images
- In center of macula
- Most cones are here
- No S-cones
- Fovea = L & M cones; v. sharp
- Parafovea = S & rods; sharpish
- Periforvea = Outer region, poor acuity, mostly rods
- Retina
- Net of layers
- Ganglion cells = to brain
- Amacrine cells = interneurons
- Bipolar cells = receptor output
- Horizontal cells = sharp edges
- Rod & Cones
- Two separate system; work together & separately
- Scotopic system (rods)
- Photopic system (cones)
- Rods
- Outside rods
- narrow and cylindrical in shape
- filled with rod disks
- Inside rods
- Rod disks
- 900 free-floating lamellae
- Floating in cytoplasm
- Contain visual purple (rhodopsin)
- Like ink in laser printer
- Can’t process purple light
- Cell nucleus
- Rod spherule = fiber ending in a single end-bulb
- Rod disks
- Polarization
- Normal neuron
- -70mV resting potential
- depolarizes to +40mV.
- Rods resting potential is -30mV
- Hit by light
- Hyperpolarizes to -60mV
- Connect to bipolar cells
- Many rods to one ganglion
- Spatial summation
- Outside rods
- Rods & Cones Comparison
- Rods
- Rods are peripheral
- Night vision (10k more sens.)
- Target detection
- Fast processing
- Low quality images
- Intensity & shades of gray
- Sensitive to lots of wavelengths
- Cones
- Cones are centralized
- Day vision
- Target identification
- Slow processing
- High quality images
- Color
- Sensitive to specific wavelengths
- Rods
- Cones
- Structure
- Shorter, broader, and more tapered than rods
- Have no visual purple
- Contains 1 of 3 photopigments
- Long
- Medium
- Short
- 1 to 1 connection
- 1 cone to 1 bipolar cell
- 1 bipolar to 1 ganglion cell
- 1 ganglion cell chain to brain
- Midget ganglions
- Each cone has corresponding spot in visual cortex
- Midget Ganglion Cells
- Small
- Each cone has one
- Each fovea cone has direct line to brain
- Exact location of point of light
- Wiring
- 1st route is direct to bipolar cell
- 2nd route is to horizontal cell
- horizontal then goes to bipolar
- Horizontal Cells
- 120 million rods (20:1)
- 6 million cones
- Need pattern recognition cells
- Lateral inhibition
- Horizontal cells inhibit neighbor
- Inhibit bipolar cells
- Activate 1 cone, tells next to stop
- Give very sharp lines & edges
- Amacrine cells
- Get info from bipolars
- Sent into to
- Bipolars
- Other amacrines
- Ganglions
- Bipolar cells
- Separate ones for rods and cones
- 10+ types for cones
- 1 type for rods
- Ganglion cells
- Form the optic nerve (optic tract)
- Leave eye through blind spot
- Receptor output
- Receptors signal bipolar cells
- Neurons close to center of eye
- Bipolars signal ganglion cells
- Even closer to center of eye
- Ganglion axons join together
- loop around, then out to brain
- Color Is Important
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