Lecture 16/17: Vision Flashcards
Cornea
Thick inelastic collagen Outer wall of eye Clear Fibers are parallel
Sclera
Thick inelastic collagen Opaque Randomly oriented fibers
Anterior Chamber
Between cornea and iris Clear watery aqueous humor
Iris
Vascular muscular diaphragm Has the pupil Controls diameter of pupil which is under neural control
Lens
Refracts light Optically clear and flexible
Ciliary Muscle
Connects lens to scleral wall Affects shape of lens Independent of iris/pupil
Vitreous Chamber
Optically empty inner cavity of eye Forces retina to remain in place against sclera
Retina and Choroid
Neural and vascular layers lining the inside of the scleral wall
Optic Nerve
Collection of retinal nerve axons Transmits information to optic chiasm, then optic tract, lateral geniculate body
Hyaloid Canal
Potential structure Tube left over from embryo when eye starts as tube
Where is the largest amount of refraction in the eye?
Air-Tear interface
Accomodation
Change of lens shape to change focus
Alters refractive power of lens
Natural state of the eye lens
Round Ciliary muscle contracts to let the lens be more round
Control of Accomodation
Edinger-Westphal nucleus CN III Ciliary ganglion Ciliary Nerve Ciliary Muscle
How does the eye achieve an increased depth of field?
Constricts the pupil
Sphincter Pupillae
Circular muscle: Constricts pupil size Parasympathetic control Pathway: 1. EW 2. CN III 3. Ciliary ganglion 4. Ciliary Nerve 5. Sphincter
Dilator Pupillae
Increases pupil size Sympathetic control Pathway: 1. Lateral Horn 2. Cervical Ganglion 3. Ciliary Nerve 4. Dilator muscle
What occurs when the pathway to the Dilator Pupillae is interrupted?
Horner’s Syndrome
Sympathetic Agonist that dilates pupil
Epinephrine and congeners
Parasympathetic Agonist that contricts the pupil
Acetylcholine Pilocarpine
Parasympathetic Antagonist that dilates the pupil
Atropine Homatropine Cyclopentolate Tropicamide
Retinal Pigment Epithelium
Supports photoreceptors Absorbs light and heat to prevent damage
Rods and Cones
Change light energy to synaptic energy
Interneurons
Relay, process, and modify image signals within retina
Ganglion cells
Relay, process, and modify image signals TO BRAIN
Rod Cells
No color perception Great numbers in periphery, little in center Very sensitive: Perhaps 1000 rods to one ganglion cell
Cone cells
Color vision Insensitive Located mostly in central retina Often 1:1 connections to interneurons which allows detail
Peripheral Retina
Rods only Lots of rods per ganglion cell Very sensitive No color Image locator
Central Retina
Cones mostly Usually 1:1 with ganglion cell Image resolution/analysis
Why does color blindness come about?
A type of cone cell is missing a pigment
Nerve path from lateral eye to optic nerve
Up and around
Deficit observed if lesion
- No right eye vison
- Same as 1
- Both temporal sides
- No left side vision
Optic Chiasm
Inputs from both eyes are organized and overlaid
Right and Left fields become joined
Fibers from nasal retina cross
What vision deficits would occur?
A. Blindness of ipsilateral eye
B. Bitemporal or Heteronymous hemianopsia
C. Unilateral nasal hemianopsia
D. Homonymous hemianopsia
E. Upper quadrant hemianopsia
F. Lower quadrant hemianopsia
Pupillary Light Reflex Pathway
- Retinal/Ganglion Cells
- Optic Nerve
- Optic Chiasm
- Optic Tract
- Skips LGN
- Pretectal Nucleus
Pupillary Light Processing Center
Inputs bilateral
Output to Edinger Westphal is bilateral
Summation and Averaging
Pupillary Light Reflex Efferent Pathway
- Edinger-Westphal Nucleus
- CN III
- Ciliary Ganglion in orbit
- Ciliary Nerves through sclera
- Pupillary Sphincter
Posterior Chamber
Area between the iris and the lens
Ciliary Body
Produces aqueous fluid at lateral edge of posterior chamber
Canal of Schlemm
Aqueous fluid passes through here to be resorbed
If blocked, can cause increased pressure
Zonule fibers
Suspend the lens from the peripheral ciliary body
What does the eye naturally focus on?
Things farther than 20 feet away
What happens when the ciliary muscle contracts
Since it is circular muscle fibers, the diameter will get smaller and relax the zonule fibers, letting the lens become more round
What controls the ciliary muscle?
Parasympathetics via EW nucleus
If everything is normal, what happens when you shine light in one eye?
Both pupils will constrict
Light test: R eye doesn’t constrict with ipsilateral light
Constricts with contralateral light
Only the optic nerve of the R eye is damaged
Light test: The R eye doesn’t constrict with light in either eye
The L eye still constricts with light in both eyes
Oculomotor nerve/nucleus of the R eye is damaged
Mueller’s Muscle
Smooth muscle that helps open the upper eyelid
Disabled in Horner’s Syndrome
What are the two different layers of the retina?
Nuclear- cell bodies
Plexiform- Axons and dendritic processes
What are the four layers of the retina specifically called?
- Starting from outer
- Photoreceptor Layer- light transducing cells
- Interneuron layer
- Ganglion cell layer- cell bodies
- Nerve fiber layer- axons to the optic nerve
Optic Disc
Place in retina where nerves leave and blood vessels enter the eye
Fovea
Half thickness
Specialized best acuity in center vision
Retinal Pigment Epithelium
Contains melanin
Prevents scatter of light and acts as heat sink
Where are cone cells greatest in number?
Fovea; center
Where are rods greatest in number?
Perifovea, periphery
Rhodopsin
Pigment in rods
Only indicates presence or absence of light
Lamina Cribrosa
Barrier where the optic nerve leaves the eye that separates CSF from fluid in the eye
Where do ganglion cells first become myelinated?
When they leave the eye
Myelin absorbs light
Optic tract
Optic nerves after they have passed through the optic chiasm
Lateral Geniculate Body
Left sees right and vice versa
Topographically aligns retinal projections
Segregates visual signals
Gateway that controls signals to cortex
Other names for Primary Visual Cortex
- V1 in occipital lobe
- Area 17
- Stria of Gennari
- Striate Cortex
- Calcarine Cortex
Describe the light reflex for a damaged right optic nerve
Describe the light reflex for a damaged right oculomotor nerve
