Anatomy & Physiology - Eye & Vision 1 Flashcards
Name the three layers of the eye ball
- Fibrous 2. Vascular 3. Inner (Retina)
Name the two parts of the fibrous layer.
- Cornea = anterior 1/6 2. Sclera = posterior 5/6
What is the external sheet of the cornea made of?
Stratified squamous epithelium
What is the corneal endothelium (deep epithelial sheet) composed of?.
Simple squamous endothelium
List two features of the cornea that allow it to keep its transparency
- No blood vessels 2. Active sodium pumps in corneal endothelium
What is the constant pressure in the cornea
There is a constant intraocular pressure pushing aq humour into stroma
What is the benefit of the endothelial pump
Maintains clarity of cornea by keeping water content low.
What is the function of the sclera?
Provides anchoring site for extrinsic eye muscles
Name the three parts of the vascular layer.
- Choroid 2. Ciliary body 3. Iris
What is the function of the choroid?
- Supplies blood to all 3 layers of the eye. 2. Melanocytes absorb light and prevent it from scattering.
What is the function of the iris?
Controls diameter of pupil regulating amount of light admitted to eye.
What muscles control the iris functions
- Dilator pupillae - radial muscle 2. Sphincter pupillae - circular muscle
List the two functions of the ciliary body
- Smooth muscle bundles control shape of lens 2. Produces aqueous humor.
Describe the vascularity of the retina.
- Inner 2/3 supplied by central artery and central vein of the artery. 2. Outer 1/3 - supplied by blood vessels in choroid
Describe the histology of the fovea centralis
- Avascular. 2. Contains only cones. 3. Outer layers of retina displaced - allows light to pass directly to cones.
How does the eye focus an image on the retina?
Ciliary muscles and ciliary zonule change shape of lens.
What is the anatomical positioning of the lens
Sits behind the pupil suspended from ciliary body by sensory ligaments in a 360 degree fashion
Describe the structure of the lens
- Avascular 2. Biconvex 3. Enclosed in thin, elastic capsule. 4. Flexible 5. Transparent
Why is it harder for eye to focus as we get older age?
- Cuboidal cells in lens ==> new lens fibers continually 2. Lens gets larger, denser, more convex, and less elastic.
What structure separates the anterior and posterior segments of the eye?
The lens.
Describe the structure of the anterior segment?
- Divided into 2 chambers - anterior and posterior - by iris. 2. Filled with aqueous humor.
Name the two muscles of the eyelid and describe their functions.
- Levator palpebrae superioris - elevates to open 2. Obicularis oculi - contracts to close
What is the conjuctivia
Membrane that lines the inside of the eye lid and the sclera infront - doesn’t extend over cornea
True or False. The mucous membrane that lines the eyelids and is reflected over the anterior surface of the eyeball is the conjunctiva.
True
True or False. Vitamin A needed by the photoreceptor cells is stored by the cells of the retina pigmented layer.
False. Stored by the retinals.
True or False. The optic disc is forms a blind spot where the optic nerve leaves the eyeball.
True
True or False. Ciliary muscles are considered voluntary, skeletal muscle.
False. Ciliary muscles are controlled by parasympathetic fibers of the oculomotor nerve.
True or False. The neural layer of the retina prevents excessive scattering of light within the eye.
False. The pigmented layer prevents excessive scattering of light.
True or False. Light passes through the entire thickness of the neural layer of the retina to excite the photoreceptors.
True.
The cornea and lens (in the anterior segment) are avascular. Explain how they remove waste and receive nutrients.
- Aqueous humor forms by filtration from the capillaries in the ciliary processes of the vascular layer. 2. Flows from posterior chamber through pupil to anterior chamber (carrying nutrients). 3. Reabsorbed into blood via the scleral venous sinus (removing wastes).
True or False. Seventy percent of all sensory receptors can be found in the eye.
True
The cornea is the only tissue that can be transplanted without rejection. Why?
Avascular, so immune system can’t reach it.
What prevents the eyelids from sticking together?
Tarsal gland secretions
Name the layers of the retina.
- Pigmented layer (outer). 2. Neural layer (inner).
List 4 types of cell found in the retina
- Photoreceptors 2. Amacrine cells 3. Horizontal cells 4. Glia
Describe the function of the fovea centralis.
Provides high visual activity (sharp, detailed vision).
Name the two regions of the lens.
- Lens epithelium. 2. Lens fibers.
Describe the structure of lens fibers
- No nuclei 2. Few organelles 3. Crystallins (folded proteins) 4. Onion-like layers
What type of cells are found in the lens epithelium
cuboidal epithelial
How does the eye focus an image on the retina for distant vision?
Sympathetic input makes: 1. Ciliary muscles relax 2. Ciliary zonule tense 3. Lens flatten
How does the eye focus an image on the retina for close vision?
Parasympathetic input makes: 1. Ciliary muscles contract. 2. Ciliary zonule loosen. 3. Lens bulge
What 3 processes must occur to restore focus during close vision?
- Accommodation (increase refractory power of lens) 2. Constriction of the pupils (accommodation pupillary reflex) 3. Convergence of the eyeballs.
What is presbyopia?
The gradual loss of accommodation due to the decreasing lens elasticity; usually in people over 50.
Which branch of the nervous system controls convergence of the eyeballs?
The somatic motor fibers of the oculomotor nerves.
Why do your eyes get tired after long periods of reading, or smartphone use? What helps?
Actions require continuous accommodation, pupillary constriction, and convergence. Focusing on distance objects relaxes intrinsic muscles.
What is the function of vitreous humor and where is it found?
- Transmits light 2. Supports posterior aspect of lens 3. Holds neural layer against pigmented layer 4. Contributes to intraocular pressure (counteracts muscles). Found in posterior segment.
List the six extrinsic muscles of the eye and describe their action and innervation.
- Lateral rectus - laterally - abducens (VI) 2. Medial rectus - medially - oculomotor (III) 3. Superior rectus - elevate & medially - oculomotor (III) 4. Inferior rectus - depress & medially - oculomotor (III) 5. Superior oblique - elevate & laterally - oculomotor (III) 6. Inferior oblique - depress & laterally - trochlear (IV)
True or False. The bending of light rays is called reflection.
False. Refraction is the correct term.
True or False. Contraction of the ciliary muscle causes the lens to bend the light less.
False. Contraction tenses the ciliary processes causing the lens to bulge and bend light more (close vision; divergent rays)
Describe the path of light through the eye
- cornea 2.aqueous humor 3. lens 4. vitreous humor
Define refraction
change in direction (bending) of light ray due to change in speed as it crosses from one medium to another at an angle other than 90o.
Describe the effect of convex and concave lenses on light rays
- Convex - converges (bend together)
- Concave - diverges (bends away)
Which parts of the eye refract light?
- Cornea
- Aqueous humor
- Lens (entering and exiting)
Which part of the eye has the greatest refractive power?
Cornea
Define accommodation
A process that increases the refractory (bending) power of the lens.
Which muscle controls the accommodation pupillary reflex?
Spinchter pupillae
Which branch of the nervous system controls the spinchter pupillae?
parasympathetic
Which muscles are used during convergence of the eyeballs?
Medial rectus of each eye
Where do the 4 rectus muscles originate?
common tendinous ring at the back of the eyeball
What is the anatomical term for a normal eye?
emmertopic
List 4 refractive problems causing homeostatic imbalance.
- Astigmatism
- Hyperopia (farsightedness)
- Myopia (shortsightedness)
- Prebyopia
List 2 ways to correct myopia?
- Concave lenses to diverge light before entering the eye.
- Laser surgery to flatten cornea.
Define and describe hyperopia?
- Farsightedness
- Eyeball is too short.
- Light rays focus behind retina.
- Can see distant objects - ciliary muscles contract continuously; increases refraction; focal point moved forward.
- Close objects blurred - focal point too far behind retina even @ full refractory power.
How is hyperopia corrected?
Convex corrective lenses.
Define and describe astigmatism. How is it corrected?
Unequal curvature in parts of cornea or lens lead to blurry images.
Special cylindrically ground lenses or laser surgery.
Compare the refractive power of corneas and lenses.
Corneas have the greatest refractory power, but its power is constant. Lenses are highly elastic, so curvature and refractive power can adapt to allow for fine focusing.
Define and describe myopia
- Shortsightedness.
- Eyeball is too long.
- Unequal curvature in parts of cornea or lens lead to blurry images.
- Can see close objects, but distant objects blurred.
Define and describe chalazion.
An unsightly cyst due to an infected tarsal gland.
Explaiin why a cold or nasal inflammation may cause the lacrimal mucosa to swell.
The nasal cavity mucosa is continuous with the mucosa in the lacrimal duct.
Define and describe glaucoma. What happens if left untreated? How is it detected? How is it treated?
- Aqueous humor is unable to drain.
- Dangerous level of pressure within the eye compresses retina and optic nerve. May result in blindess.
- IOP is determined by measuring extent of corneal deformation caused by puff of air.
- Eye drops increase rate of aqueous humor production drainage, or decrease rate of production. Laser therapy of surgery can also help.
What is a cataract?
Clouding of lens that distorts vision (frosty glass).
List 5 causes of cataracts.
- Sometimes congenital;
- Most due to age-related hardening and thickening of lens;
- Secondary consequence of diabetes mellitus;
- Heavy smoking;
- Frequent exposure to sunglight
List 2 reasons cataracts form?
- Oxidative stress and metabolic changes in deeper lens fibers cause crystallin proteins to clump.
- Vitamin C may increase cataract formation.
How are cataracts treated?
Replacement of damaged lens with an artificial lens.
