Special Senses: Special Senses: VisionVision

Chapter 8Chapter 8

AgendaAgenda

Anatomy of the eye – internal Anatomy of the eye – internal and externaland external

Light and light refractionLight and light refraction

Diseases and disorders of the Diseases and disorders of the eyeeye

The Eye and VisionThe Eye and Vision

Special sense receptors – large, Special sense receptors – large, complex sensory organcomplex sensory organ

70% of sensory receptors70% of sensory receptors

Optic nerve – 1+ million nerve fibersOptic nerve – 1+ million nerve fibers

External and Accessory External and Accessory Structures of EyeStructures of Eye

Extrinsic eye musclesExtrinsic eye muscles

Figure 8.3a

External and Accessory External and Accessory Structures of EyeStructures of Eye

Eyelids – eyelashesEyelids – eyelashes Tarsal glands - Tarsal glands -

lubricationlubrication ConjunctivaConjunctiva Lacrimal Lacrimal

ApparatusApparatus

http://www.virtualmedicalcentre.com/anatomy.asp?sid=28http://www.wisedude.com/health_medicine/eyelids.htm

Conjunctivitis – Pink EyeConjunctivitis – Pink Eye

Conjunctivitis – Conjunctivitis – inflammation of inflammation of conjunctivaconjunctiva

Pink Eye – Pink Eye – Infection of Infection of conjunctiva by conjunctiva by bacteria or virus, bacteria or virus, highly contagioushighly contagious

Leads to red, Leads to red, irritated eyesirritated eyes

https://www.bcbsri.com/BCBSRIWeb/images/mayo_popup/Pinkeye(conjunctivitis).jsp

Internal Anatomy of EyeInternal Anatomy of Eye Humors Humors

Vitreous - Vitreous - posteriorposterior

Aqueous – Aqueous – anterioranterior

LensLens

Wall – 3 layersWall – 3 layers Fibrous layerFibrous layer Vascular layerVascular layer Sensory layerSensory layer

Figure 8.4a

Figure 8.4b

Wall of Eye Wall of Eye

Fibrous Layer – 2 Fibrous Layer – 2 partsparts Sclera – protective, Sclera – protective,

white of eyewhite of eye Cornea – crystal Cornea – crystal

clear, many nerve clear, many nerve endings, vulnerable, endings, vulnerable, extraordinary healingextraordinary healing

Only tissue in body Only tissue in body that can be that can be transplanted w/o fear transplanted w/o fear of rejection – no blood of rejection – no blood vessels immune vessels immune system can’t reachsystem can’t reach http://www.vision-training.com/en/Eye%20Anatomy/Eye%20anatomy.html

Wall of EyeWall of Eye Vascular Layer – 3 Vascular Layer – 3

regionsregions Choroid – blood rich, Choroid – blood rich,

dark pigment, light dark pigment, light scatterscatter

Ciliary body – muscle Ciliary body – muscle structure, lens structure, lens attached via ciliary attached via ciliary zonule (suspensory zonule (suspensory ligament)ligament)

Iris – muscle Iris – muscle structure, pigmented, structure, pigmented, rounded opening rounded opening (pupil), smooth muscle (pupil), smooth muscle

http://canyouspellhubbell.com/wordpress/?p=15

Wall of EyeWall of Eye Sensory Layer – 2 Sensory Layer – 2

layer retinalayer retina Extends to ciliary Extends to ciliary

bodybody Outer layer – Outer layer –

Pigmented LayerPigmented Layer Pigmented cells – Pigmented cells –

absorb and prevent absorb and prevent light scatteringlight scattering

What other structure What other structure also does this?also does this?

Cells act as Cells act as phagocytesphagocytes

Figure 8.5b

Wall of EyeWall of Eye

Sensory Layer – 2 Sensory Layer – 2 layer retinalayer retina Extends to ciliary Extends to ciliary

bodybody Inner Layer – Inner Layer –

Neural LayerNeural Layer TransparentTransparent Contains millions of Contains millions of

photorectptors- photorectptors- cones and rodscones and rods

Figure 8.5

Nerve Impulses from Nerve Impulses from RetinaRetina

Electrical signals Electrical signals from photoreceptors from photoreceptors leave retina as nerve leave retina as nerve impulses via optic impulses via optic nervenerve

Transmitted to optic Transmitted to optic cortex = visioncortex = vision

Photoreceptors on Photoreceptors on entire retina except entire retina except where optic nerve where optic nerve leaves eyeball = optic leaves eyeball = optic disk or blind spotdisk or blind spot

PhotoreceptorsPhotoreceptors Cones – most dense at Cones – most dense at

center of retina, center of retina, decrease on peripherydecrease on periphery Color under bright Color under bright

conditionsconditions Macula lutea, fovea Macula lutea, fovea

centraliscentralis 3 types – sensitive to 3 types – sensitive to

different wavelengthsdifferent wavelengths BlueBlue GreenGreen Green and Red (called Green and Red (called

red)red) ‘‘mixing’ in brainmixing’ in brain http://pro.corbis.com/search/Enlargement.aspx?CID=isg&mediauid=%7B0CA81D50-A4C0-40AE-B9FF-

351B3485A49E%7D

PhotoreceptorsPhotoreceptors

Rods – more dense at periphery, Rods – more dense at periphery, decrease in number towards centerdecrease in number towards center See grey tones in dim lightSee grey tones in dim light Provides peripheral visionProvides peripheral vision

Night or Color BlindnessNight or Color Blindness

Color Blindness – More common in men, Color Blindness – More common in men, most common is lack of red or green most common is lack of red or green receptorsreceptors See red or green as same color, depends on See red or green as same color, depends on

cones presentcones present Can see differences in intensity of colorCan see differences in intensity of color

Night Blindness – most commonly caused Night Blindness – most commonly caused by Vitamin A deficiency, leads to by Vitamin A deficiency, leads to deterioration of neural retinadeterioration of neural retina Vitamin A supplements can restore if Vitamin A supplements can restore if

degenerative changes have not occurreddegenerative changes have not occurred

LensLens

Divides eye into 2 segmentsDivides eye into 2 segments Anterior (Aqueous) SegmentAnterior (Aqueous) Segment

Similar to blood plasmaSimilar to blood plasma Continuously secreted by part of choroidContinuously secreted by part of choroid Provides nutrients for lens and cornea, lack blood Provides nutrients for lens and cornea, lack blood

supplysupply Reabsorbed into venous blood through canal of Reabsorbed into venous blood through canal of

SchlemmSchlemm Posterior (Vitreous) SegmentPosterior (Vitreous) Segment

Gel-like substanceGel-like substance

Both maintain intraocular pressureBoth maintain intraocular pressure

GlaucomaGlaucoma

Drainage of aqueous Drainage of aqueous fluid via canal of fluid via canal of Schlemm blockedSchlemm blocked

pressure increases pressure increases compressing retina compressing retina and optic nerve, and optic nerve, causes pain and causes pain and possibly blindness possibly blindness

Common in elderlyCommon in elderly Slow processSlow process

http://www.steadyhealth.com/articles/Can_Glaucoma_Be_Prevented__a640_f0.html

LensLens

Focuses light Focuses light entering entering retinaretina

BiconvexBiconvex Held upright Held upright

by suspensory by suspensory ligaments – ligaments – ciliary zonule ciliary zonule attached to attached to ciliary bodyciliary body

http://projects.cbe.ab.ca/Diefenbaker/Biology/Bio%20Website%20Final/notes/nervous_system/8_eye_notes.html

Light RefractionLight Refraction Refraction = bending of light Refraction = bending of light

due to change in speeddue to change in speed Refractive power of cornea, Refractive power of cornea,

and humors constantand humors constant Refractive power of lens Refractive power of lens

changeschanges Goal to focus light at one Goal to focus light at one

point on back of eyepoint on back of eye How does lens change to do How does lens change to do

this?this? Distant vision – light enters Distant vision – light enters

as parallel rays, lens does not as parallel rays, lens does not need to change shapeneed to change shape

Close vision – divergent rays, Close vision – divergent rays, lens must bulge more = lens must bulge more = accommodationaccommodation

Nearsighted or Nearsighted or FarsightedFarsighted

CataractsCataracts

With age, lens With age, lens becomes hard and becomes hard and opaqueopaque

Diabetes mellitusDiabetes mellitus Heavy smokingHeavy smoking Vision becomes hazy Vision becomes hazy

and distorted, will and distorted, will lead to blindnesslead to blindness

Surgical removal or Surgical removal or glassesglasses

http://www.ehponline.org/docs/2005/113-3/niehsnews.html

Binocular visionBinocular vision

““two-eyed” visiontwo-eyed” vision

Provides depth Provides depth perceptionperception

3D vision3D vision

http://www.e-advisor.us/visual_fields.htm

Eye ReflexesEye Reflexes

Convergence = movement of eyes Convergence = movement of eyes medially when viewing close objectsmedially when viewing close objects

Photopupillary reflex = pupils Photopupillary reflex = pupils constrict in bright light to protect constrict in bright light to protect photoreceptorsphotoreceptors

Accommodation pupillary reflex = Accommodation pupillary reflex = pupils constrict when viewing close pupils constrict when viewing close objectsobjects

The EndThe End