Download Biomechanics of Eye

BiomechanicsofEye
Anatomyofeye
AnatomyoftheEye
Func3onsVs.Physiology
ImportantlayersofCornea
Cataract
Cataract
Glaucoma
Glaucoma
DevelopmentofGlaucoma
DevelopmentofGlaucoma
DevelopmentofGlaucoma
GlaucomaDamage
OpenVs.ClosedAngleGlaucoma
GlaucomaEffect
Glaucoma
BlackVs.Whiteblindness
OCULARMUSCLEFUNCTIONS
Musclesoftheeye–responsiblefor
ocularmovement
Musclesoftheeye–responsiblefor
ocularmovement
Musclesoftheeye–responsiblefor
ocularmovement
IndividualMuscleFunc3ons
IndividualMuscleFunc3ons
Eachofthesixextraocularmusclesplaysaroleinposi3oningtheeye
aboutthreeaxesofrota3on.Theprimaryac3onofamuscleisthe
principaleffectithasoneyerota3on.Lessereffectsarecalledsecondary
orter3aryac3ons.Theexactac3onofanymuscledependsonthe
direc3onoftheeyeinspace.
SurgicalCorrec3onofOcularmuscles
FOCUSING
© 2013 Pearson Education, Inc.
Point sources
Focal points
Focusing of two points of light.
The image is inverted—upside down and reversed.
© 2013 Pearson Education, Inc.
Focusing Light on The Retina
•  Pathway of light entering eye: cornea, aqueous
humor, lens, vitreous humor, entire neural layer
of retina, photoreceptors
•  Light refracted at boundaries along pathway
–  Air to cornea/aqueous humor
–  Aqueous humor to lens
–  Lens to vitreous humor
•  Most bending happens at air-cornea boundary
•  Lens curvature is the “fine adjustment”
© 2013 Pearson Education, Inc.
Focusing For Distant Vision
•  Eyes best adapted for distant vision
•  Far point of vision
–  Distance beyond which no change in lens shape
needed for focusing
•  20 feet for emmetropic (normal) eye
•  Cornea and lens focus light precisely on retina
•  Ciliary muscles relaxed
•  Lens stretched flat by tension in ciliary zonule
© 2013 Pearson Education, Inc.
Sympathetic activation
Nearly parallel rays
from distant object
Lens
Ciliary zonule
Ciliary muscle
Inverted
image
Lens flattens for distant vision. Sympathetic input
relaxes the ciliary muscle, tightening the ciliary zonule,
and flattening the lens.
© 2013 Pearson Education, Inc.
Focusing For Close Vision
•  Light from close objects (<6 m) diverges
as approaches eye
–  Requires eye to make active adjustments
using three simultaneous processes
•  Accommodation of lenses
•  Constriction of pupils
•  Convergence of eyeballs
© 2013 Pearson Education, Inc.
Focusing For Close Vision
•  Accommodation
–  Changing lens shape to increase refraction
–  Near point of vision
•  Closest point on which the eye can focus
–  Presbyopia—loss of accommodation over age 50
•  Constriction
–  Accommodation pupillary reflex constricts pupils to
prevent most divergent light rays from entering eye
•  Convergence
–  Medial rotation of eyeballs toward object being viewed
© 2013 Pearson Education, Inc.
Parasympathetic activation
Divergent rays
Inverted
from close object
image
Lens bulges for close vision. Parasympathetic input
contracts the ciliary muscle, loosening the ciliary zonule,
allowing the lens to bulge.
© 2013 Pearson Education, Inc.
Problems Of Refraction
•  Myopia (nearsightedness)
–  Focal point in front of retina, e.g., eyeball too long
–  Corrected with a concave lens
•  Hyperopia (farsightedness)
–  Focal point behind retina, e.g., eyeball too short
–  Corrected with a convex lens
•  Astigmatism
–  Unequal curvatures in different parts of cornea or lens
–  Corrected with cylindrically ground lenses or laser
procedures
© 2013 Pearson Education, Inc.
Emmetropic eye (normal)
Focal
plane
Focal point is
on retina.
© 2013 Pearson Education, Inc.
Myopic eye (nearsighted)
Eyeball
too long
Uncorrected
Focal point is in
front of retina.
Corrected
© 2013 Pearson Education, Inc.
Concave lens moves focal
point further back.
Hyperopic eye (farsighted)
Eyeball
too short
Uncorrected
Focal point is
behind retina.
Corrected
© 2013 Pearson Education, Inc.
Convex lens moves focal
point forward.
Functional Anatomy Of
Photoreceptors
•  Rods and cones
–  Modified neurons
–  Receptive regions called outer segments
•  Contain visual pigments (photopigments)
–  Molecules change shape as absorb light
–  Inner segment of each joins cell body
© 2013 Pearson Education, Inc.
PHOTORECEPTION
Photorecep3on
ConeandRodcelldistribu3on
ConeandRodcelldistribu3on
Conearesensi3vetocolor(i.e.wavelength)
Rodsarenotsensi3vetocolor
Rodsaremoresensi3vetolightthancones
(intensity)
Absorp3onspectraofHumanVisual
Pigments
ConecellsandRodCells
ChipinSynthe3cvisualsensor
Re3naldisease
•  Largenumberofprogressivere3nal
degenera3onsthatpredominately
affectthephotoreceptorlayeror
“lightsensing”cellularlayerofthe
re3na.
•  Danbehereditaryordevelopasa
newcondi3on
•  Willworsenwith3me.
AMDprimarilyaffectsthehighestresolu3on
centralpor3onofthere3naknowntoasthe
macula
Producesa“dry”orgeographicformof
damageresul3nginblindspots.
DryAMDmayprogressintolargerareasof
visionlosswiththedevelopmentofa“wet”
formthatoccursfrombloodvessel,withinthe
affectedre3nalareasleakingorbleeding.
Scarringofthesere3nalareasmayalsooccur.
MEASUREMENTOFINTRAOCULAR
PRESSURES(EYEPRESSURE)
IntraocularPressure
•  Normal–10to21mmofHg
•  Higherthan21mmofHgisocular
hypertension
•  Lowerthan5mmofHgistermedashypotony
•  Higherthan21mmofHgdoesnotmeana
personhasglaucomabuthastherisktobe
affectedwithhighpressure.
Tonometers
Indenta3ontype
Tonometers
Applana3ontype(Contact)
NoncontactTonometers
Applana3ontype(Non-Contact)
IOP
LASIKSurgery