Visual System Part 1: Eye Structures Flashcards by Jennifer Tarbet

How is perception different from sensation?

Sensation is sensory information.
Perception is sensory information that is interpreted or given meaning based on memories, emotions, context, prior knowledge.

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How is the dorsal stream different from the ventral stream of information processing in the brain?

Dorsal stream = “where” (location, movement, spatial transformations/relationships) occurs in parietal
Ventral stream = “what” (color, texture, pictorial detail, shape, size) occurs in temporal lobe

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Describe the feedback loop involved in sensation?

Pigments absorb light
Receptors sample small amts of energy (env. stimuli) and generate AP
Train of nerve impulses via nerve pathway to CNS
CNS feedback regulates pigments and sensory receptors to maintain tolerable level of stimulation

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What structure in the eye is homologous to dura?
Arachnoid and pia?
CNS?

Dura –> Sclera (fibrous)
Arachnoid and pia –> Choroid (vascular)
CNS–> Retina (nervous)

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Sclera is what type of tissue? What muscles insert?

Dense, white CT with collagen and blood vessels. Extrinsic muscles of eye insert.

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What structure is continuous with the sclera? How is it different from sclera? How is it nourished?

Cornea. Continuous but clear, avascular. Draw nutrients from aqueous humor by diffusion.

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What is the uveal tract? What is uveitis?

Vascular coat = choroid, ciliary body/muscle, iris
has “prolific vasculature”
Uveitis = inflammation of uvea caused by ??

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___________ controls the refraction of light by the lens.

___________ controls the amount of light entering eye.

Ciliary body/muscle (ciliary body = muscle + process)

Iris

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Most refraction is done by the _________.

Cornea (corneal stroma) - 2/3 of refractive power of eye

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What are the 5 layers of the cornea and their functions?

Strat. squam. non-keratinizing epithelium
Bowman’s (basement) membrane - reduces infection
Stroma fibroblasts - generate orthogonal lamellae of collagen fibers
Descemet’s (basement) membrane
Simple squamous endothelium - conveys metab. substances and H2O from aq. humor to cornea

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Describe the replenishment/regeneration of the cornea.

Stem cells in the adjacent corneoscleral limbus (in between conjunctiva and cornea) generate Transient Amplifying Cells (TACs), which migrate to replenish corneal epithelium.

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How is corneal DNA protected from UV?

Ferretin

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How is the lens similar to the cornea?

Clear, avascular, nourished through diffusion.

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The lens is connected to the ciliary body/muscle by ___________________.
These are _______ fibers that are contractile/noncontractile?

Zonular fibers of suspensory ligaments
CT fibers
Non-contractile

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Resting convexivity of the lens is maintained by

Outward pull of suspensory ligaments from ciliary body. Inward pull by intrinsic elastic fibers (collagen IV and glycoprotein) in lens.

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Can the lens produce new elastic fibers throughout life? Are germinal lens cells clear?

Yes. Germinal zone.

No. Cells lose nuclei and become transparent after migration from germinal zone.

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What is presbyopia and what causes it?

Presbyopia (far sightedness) = age related loss of resting convexivity caused by loss of elasticity.

What is cataracts and what causes it?

Cataracts = reduction of vision due to opaqueness of the lens. 
Oxidative damage (via UV) causative factor. 
Ox. damage largely by iron-catalyzed free radical rxns. Iron level increased in cataractous lenses.

Describe the changes in the lens (and muscles/ligaments)when looking at a distant object in a normal eye.

Distant object = less refraction needed = ciliary muscle relaxes = susp ligaments tighten = flatter lens = decreased convexivity

What is accommodation?

Convexivity of the lens is altered by ciliary body to compensate for distance of objects

In myopia, the eyeball is too _____ short/long and light is focused ______ in front of/behind the retina.

Myopia (near sighted) = Eyeball too long and light is focused in front of retina

Describe the generation and flow of aqueous humor through the eye and into the venous system.

Ciliary processes secrete humor 
into posterior chamber 
flows into anterior chamber 
flows into Schlemm's canal (scleral venous sinus) 
absorbed into venous system.

What is glaucoma? What causes it? What is the result?

Build up of fluid pressure due to inadequate drainage into Schlemms’ canal.
Causes - adherence of iris to lens (block flow), iris presses against corneoscleral angle (block canal). Intraoccular pressure can damage optic nerve.

What are the tissue layers of the iris? Do they transmit or refract/reflect light?

Stroma = CT + b.v. + melanocytes + fibroblasts
Constrictor and dilator pupillae
Pigment epithelium = continuous on post. surface of iris, completely absorbs all light (limits light into pupil)
Layers of iris are opaque (barrier to light)

What is Rayleigh scattering? How does it affect the color of the sky?

Sunlight scattered by atmospheric gases and particles. Blue sky = sun overhead = shorter path = atmospheric particles scatter blue light. (Blue is scattered more than other colors b/c shorter wavelength) Red sunset = sun low = longer path = almost all blue light has been scattered out = white minus blue equals red/orange/yellow. http://spaceplace.nasa.gov/blue-sky/en/

Where is melanin found in the iris?

Melanocytes are found in the stroma but primarily in the pigment epithelium (posterior iris)

For each say T/F A. In blue eyes, melanin is mostly in pigment epithelium. B. In brn/grn eyes, melanin in stroma absorbs blue light. C. In blue eyes, melanin in the stroma refracts blue light. D. Melanin absorbs red/yellow and reflects blu/grn. E. The more melanin, the darker the eye color.

A. True. B. True. C. False. Turbid medium of stroma refracts blue light. D. False. Absorbs blu/grn and reflects red/yel. E. True. more absorption of blu/grn and reflection of red/yel = darker eye color

Describe the path of nerve impulses and the muscles that constrict the pupil?

Parasymp. nerve impulse --> CN III --> ciliary ganglion --> follow choroid to sphincter pupillae --> constricts pupil

Is pupil size directly or inversely related to focal range?

Pupil size is inversely related to focal range.

Where does the occulomotor nerve enter the orbit? What other nerves travel with CN III?

Superior orbital fissure. CN IV and VI.

What are eye floaters?

Black or grey specs, strings, or cobwebs that drift when you move your eyes.

What is the vitreous humor made of?

Hyaluronic acid, type II collagen fibrils, glycosaminoglycans, 99% H2O

What is the hyaloid canal?

Vestige of hyaloid artery used to nourish embryonic lens and vitreous humor. Blood and cell debris removed by phagocytes but residual pieces remain.

For each answer say T or F A. Neural tube is derived from ectoderm. B. Neural tube forms optic vesicles and lens placode. C. Invaginating optic vesicle forms neural (anterior) and pigmented (posterior) retinal layers.

A. True B. False. Lens placode derived from ectoderm, not neural tissue. C. True

What tissues surround the optic nerve?

Dura, arachnoid, pia, and subarachnoid space

What is the RPE?

Retinal pigmented epithelium

Describe the changes in the lens (and muscles/ligaments)when looking at an object close up in a normal eye.

Near vision = more refraction needed = ciliary muscle contracts = susp. ligaments slacken = thicker/bulgier lens = increased convexivity

In hyperopia the eyeball is too _____ short/long and light is focused ______ in front of/behind the retina.

Hyperopia (far sighted) = Eyeball too short and light is focused behind retina http://www.kontur55.com/vision-101.html

Describe the path of nerve impulses and the muscles that dilate the pupil?

Symp. nerve impulse --> upper thoracic spinal cord --> superior cervical ganglion --> follow choroid to dilator pupillae --> dilates pupil

What are three possible causes of eye floaters?

1. W/ age vit. humor more liquid --> depolymerization of collagen --> forms mats 2. Collagen fiber bundles clump w/in vit humor and cast shadows 3. Vestiges of hyaloid artery