chapter 17

Hyperopia and how to correct

(far-sighted) results when eyeball is too short or lens is too flat. You can correct by increasing refraction. Image focuses BEHIND the retina. Eyeball is too short *see far clearly, near is blurry

Myopia and how to correct

(near-sited) results when eyeball too long or lens is too curved. Image focuses in FRONT of the retina before reaching the fovea centralis. Eyeball is too long. Correction: decrease refraction *See near clearly, far is blurry.

What happens when you are more then 20ft away (>20ft)

Ciliary muscle is relaxed. Ciliary body moves away from the lens. Tension on suspensory ligaments increases (ligaments are pulled tight). Lens will. Decrease in light bending/refraction.

What is a cataract

Clouding of the lens due to change in lens proteins (clumping of crystalline). Not enough nutrients reach deeper to lens fibers. Laser can break up clouding or have to replace lens. (can be age related)

Contraction of the lens

Contraction and closeness needs to happen to change curvature on lens so we can focus on nearby objects. (only for near, never far; we're adapted to far vision)

What is age-related macular disease (AMD) or macular degeneration

Degenerative disorder of the retina in persons 50 or older. Abnormalities occur in the region of the macula lutea. Advanced AMD will cause an inability to see straight ahead.

What are the 2 types of problems with extrinsic eye muscles

Diplopia: double vision due to paralysis/weak eye muscles Strabismus: cross eyed due to congenital weakness in eye muscles which affects rotation medially or laterally

what is the action and controlling cranial nerve for the lateral rectus muscle and medial rectus muscle

Lateral: moves eye laterally - VI abducens Medial: moves eye medially III oculomotor

Visual nervous pathway

Light ->photorecepter cells->bipolar neurons ->ganglion neurons (axons exit as optic nerve) ->optic chiasma (axons from medial half of each retina cross to the opposite side) ->optic tract ->thalamus ->visual sensory area in occipital lobe of cerebrum

What is apart of the posterior cavity

Located behind the lens. Filled with gel-like vitreous humor (body, not replaceable). Also maintains intraocular pressure. Holds the retina in place.

Neural layers of retina: photorecepter layer

RODS: Excited by low light intensity. Produces images in shades of grey. ~120 million dim light receptors. CONS: excited by high light intensity. Provides color vision. 3 kinds (blue, green & red) that are sensitive to different wavelengths of light. ~6 million bright light receptors. Macula lutea: yellow flat spot on retina Fovea Centralis: only has cons, greatest visual acuity

choroid

Vascular tunic. Darkly pigmented region. Contains blood vessels. absorbs excess light to prevent scattering (causes visual confusion). Supplies nutrients to posterior 1/3 surface. Central artery supplies 2/3 to the anterior portion.

ciliary body

Vascular tunic. Muscular ring around lens. -Ciliary muscles: smooth muscle the regulates the shape of the lens. -Ciliary processes: folds that contain blood vessels that produce aqueous humur. suspensory ligaments extend from ciliary processes to hold lens in position

Iris

Vascular tunic. pigmented part of eye. Contains circular and radial smooth muscles. Opening of iris is the pupil (light enters eye). Pigment color is from melanin.

Astigmatism

Your lens and cornea have an irregular curvature

Conversion of image to nerve impulse/activating photoreceptors

a chemical change in photopigments (photoreceptor cells) leads to a generation of an action potential. An overlap of colors allows us to see various colors. 3 cone types: red, blue ,green. We can activate more than one cone which allows us to see different colors.

Lens

avascular, biconvex structure. Held in place by suspensory ligaments. Can change shape to focus image. Cells within lens contain transparent proteins (crystalline protein)

ganglion cells - neural layer- retina

axons of neurons converge at the optic disc. Blind spot means no photorecepters at optic disc (no image). Optic disc attaches retina to the back of eye (only place its attached). Central artery and vein branch out from disc to supply anterior 2/3 of retina.

Why are corneal transplants successful

because the cornea is avascular. rejection is rare because there is no access to the immune system therefore no blood-borne antibodies

Accommodation of lens

changes in curvature of lens that enables you to focus on nearby objects. Involves the ciliary muscle which is under autonomic nervous system control.

What happens to the eye when you need to see less than 20ft (<20ft)

ciliary muscle will contract, ciliary body is pulled towards the lens. Tension on suspensory ligaments decreases (ligaments go slack). The lens shape becomes rounder. Increase in light bending/refraction.

Convergence of the eye

extrinsic eye muscles turn eyes medially for close vision

Accessory structures of the eye

eyebrows, eyelids, conjunctiva, lacrimal apparatus, extrinsic eye muscles

Anatomy of the eye

has 3 layers (tunics), no night vision, adipose tissue surrounds eyeball to cushion, cornea and sclera are the most outer layer, retina allows us to actually see, choroid is the vascular tunic, outer eye to inner eye is the method of viewing the eyeball system

Lacrimal gland and function of tears

in superior lateral region of each eye, secretes lacrimal fluid. -Tears contain water, salt, mucous, antibodies and lysozymes (antibacterial enzyme). clears, lubricates eye. Fluid doesn't spill over but extra is usually swallowed. Emotional response triggers tears (parasympathetic)

color-blindness

inability to see some or all colors. lacks 1 or more cons

What happens if aqeuous humur is not reabsorbed properly

increase in intraocular pressure. Compresses the retina and blood vessels , retina cells could die. Condition called glaucoma

what is the action and controlling cranial nerve for the inferior oblique muscle and the superior oblique muscle

inferior: elevates eye & turns it laterally III oculomotor superior: depresses eye & turns it laterally IV trochlear

What is the pathway of tears

lacrimal gland ->lacrimal duct->lacrimal fluid flows over the eye ->lacrimal punctum -> lacrimal canaliculus ->lacrimal sac -> nasolacrimal duct ->nasal cavity

How does the lens accommodate light

light from a distance object >20ft needs little to be in focus. If it is, rays are more divergent and need greater refraction. Lens becomes rounder to accommodate light.

What is light

light is a wave of energy that radiates from the sun and travels through space at high velocity. Form of electromagnetic radiation: xrays, UV rays, visible light, microwaves, radiowaves. Describes these waves in terms of their wavelength.

Explain what happens when light is bent

light is refracted (bent) as it passes through media of different densities. light passes through cornea (75% of refraction, curvature of cornea is fixed.no muscle contraction). Light enters and leaves the lens (25% remaining focusing power, curvature of lens can change). Transparent medium: air-certain density & glass-different density. Light bending needs to hit the fovea centralis.

What is apart of the anterior cavity

located in FRONT of the lens. Filled with watery aqueous humur. Maintains intraocular pressure (16-20mmHg) to support eyeball internally. Provides oxygen and nutrients to lens and cornea.

What do all photopigments contain

opsin (glycoprotein) and retinal (derivative of Vitamin A). Four kinds of opsins which allows rods (one opsin) and cones (3 opsins) to absorb different wavelengths of light.

Fibrous tunic

outermost avascular layer. Contains: sclera: posterior portion. white of eye, maintains shape, protects inner surface. Cornea: anterior transparent portion with a fixed curvature. Majority of the light bending, focuses light rays (allows light in and also bends light)

Red-green sex-linked

perceive both colors as being red or green. missing an opsin.

Retina (inner layer)

pigmented layer: closest to choroid, absorbs excess light. to reduce scattering. Neural layer: visual part of retina

Phototransduction

process of light energy being converted into a graded receptor potential. Photoreceptors (rods and cons) are modified neurons.

Bipolar layer - neural layer- retina

relay messages from photorecepters to ganglion cells.

problems with accessory eye structures

sty: infected hair follicle at base of eyelash blood shot eyes: vessels in conjunctiva over sclera get irritated and dilate Conjunctivitis: inflammation of the conjunctiva (by bacteria or virus). Highly contagious

what is the action and controlling cranial nerve for the superior rectus muscle and inferior rectus muscle

superior: elevates eye & turns it medially - III oculomotor inferior: depresses eye & turns medially - III ocolomotor

What is a detached retina?

the pigmented and neural layers of the retina separate and vitrous humur seeps between. This deprives the neural retina of its blood supply and could result in blindness.

contraction of the pupil

to see far away, the pupils dilates. To see near, the pupil constricts. Radial muscle will contract.

How can we see light

we see objects because light is reflected from their surfaces, objects absorb some wavelengths of light and reflect others *reflected light is captured by our eyes. Object appears color of the wavelength of light that is reflected off of it. Ex: apple is res because it reflects mostly red wavelength and absorbs the others.