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Block One > Multiple Levels Of Organization Of The Eye > Flashcards

Multiple Levels Of Organization Of The Eye Flashcards

1
Q

Relationship of globe to orbit and adnexa

A

Critical for vision, appearance, and health of the ye

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2
Q

Adnexa

A

Tissues around eye supporting its health

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3
Q

Orbit

A

Cone-shaped cavity containing globe and adnexa as well as other vessels, nerves, glands, fat ect.

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4
Q

Human orbit

A

Entirely bone

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5
Q

Canine orbit

A

Temporalis muscle forms lateral orbit wall and the medial pterygoid form part of the floor, zygomatic salivary gland forms more than 1/2 of the orbit floor (ie it is not entirely bone)

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6
Q

Canine rim of the orbit

A

Aka margin of the orbit, in some species entirely bone but in dog orbital ligament completes lateral margin of orbit rim

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7
Q

Bones comprising orbit walls and rim in dogs

A

Frontal, maxillary, zygomatic, and variably the lacrimal bones

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8
Q

Periorbita

A

Cone of thick connective tissue suspending Eye ball, extraocular muscles, vessels, nerves, fat, and adjacent connective tissue within orbit

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9
Q

Canine periorbita

A

Continuous with periosteum medially and dorsally
Distinct tissue ventrally and laterally
Orbit apex caudally periorbita continuous with dura matter and periosteum at optic canal/ orbital fissure

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10
Q

Orbit septum

A

Rostral at orbit rim periorbita blend into periosteum of adjacent bones and continue into eye lids as orbit septum

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11
Q

Anterior extent of orbital cavity

A

Eyelids and orbital septum define this boundary

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12
Q

What keeps eye forward in orbit

A

Periorbital connective tissue contains fine circularly arranged smooth muscle fibers exerting a constant squeeze on cone

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13
Q

Tenon’s capsule

A

Loose connective tissue immediately surrounding eyeball deep to conjunctiva

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14
Q

How is the globe suspended within periorbital cone?

A

Suspended via elaborate fascia and connective tissue networks including loose connective tissue sheets and check ligaments

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15
Q

Fat in orbit

A

Fat amounts variable between species, fat within and external to periorbita caudally, ventrally, laterally, fat cushions eye and provides room to move

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16
Q

Foramina/ fissures found in orbit

A

Optic canal, orbital fissure, rostral alar foramen, 2 ethmoidal foramina, fossa for lacriminal sac and others

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17
Q

Eyelids

A

Dorsal and ventral folds of facial skin with connective tissue for support plus muscles within them that allow lids to open and close

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18
Q

Eyelid function

A

Protect eye, remove foreign substances from surface of eye, distribute tear film, prevent tear overflow, contribute to tear film, exclude light from eyes, pump tears medially for cleansing of eye and tear remove all and more

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19
Q

Palpebral fissue

A

Space or opening between eyelids

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20
Q

Medial commissure or canthus

A

Union of free edges of upper and lower lids

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21
Q

Lateral commissure or canthus

A

Union of free edges of upper and lower lids laterally

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22
Q

Cilia

A

Eye lashes

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23
Q

How many rows eyelashes on upper lid of dog

A

2-4

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24
Q

Medial

A

Nasal

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25
Q

Lateral

A

Temporal

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26
Q

Tacticle hairs

A

Analagos to eyebrows

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27
Q

Lacrimal carbuncle

A

Small mound of tissue just inside medial canthus often haired; contains glands, serves to divert or redirect tears toward lacrimal puncta

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28
Q

Eyelid muscles

A

Orbicularis oculi, lavator palpebreal superious, tarsal muscles,+ more we don’t need to know names of

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29
Q

Orbicularis oculi

A

Oval sphincter like skeletal muscle beneath skin, closes lids in resposne to somatic efferent impulses

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30
Q

Orbicularis oculi innervation

A

Somatic efferent impulses; innervated by palpebral branch of cranial nerve VII

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31
Q

Orbicularis oculi anchoring

A

Anchored medially and laterally by ligaments

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32
Q

Absence of medial and lateral ligaments anchoring orbicularis oculi

A

If these are absent stretched or lacerated then palpebreal fissures can close like other fissures surrounded by sphincters

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33
Q

Levator palpebral superioris

A

Skeletal muscle, retracts upper lid, thin flat muscle works in unison with dorsal rectus muscle which it is dorsal to

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34
Q

Levator palpebral superioris innervation

A

Skeletal muscle, innervated by cranial nerve III to retract upper lid

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35
Q

Tarsal muscles

A

Ie Mueller’s muscle; smooth muscles that retract (open lid) sympathetic innervation

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36
Q

Medial levator annuli oculi

A

Eyelid miscue, raises eyebrow gives expression

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37
Q

Eyelid gland

A

Tarsal gland (meibomian glands); there are others we aren’t worrying about for block 1

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38
Q

Tarsal glands

A

Ie meibomain glands; sebaceous glands of upper and lower lids that form oily, outer layer of tear film, visible through conjunctiva, perpendicular to lid margins, parallel white yellow lines

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39
Q

Tarsal gland opening

A

Open in a furrow on lid margin (dotted line called gray line)

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40
Q

Eyelid connective tissue

A

Tarsus (aka tarsal plate) and ligaments

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41
Q

Tarsus

A

Ie tarsal plate; fiberous thickening surrounding tarsal glands at lid margins that continues into each eyelid blending into orbit septum and periosteum near orbit rim; VERY important to lid support

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42
Q

Ligaments of eye lid connective tissue

A

Medial and lateral cantonal ligaments extend from tarsus to orbital periosteum

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43
Q

Medial canthal ligament

A

Well developed in all breeds

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44
Q

Lateral canthal ligament

A

Poorly developed in some dog breeds, may be muscular or musculofibrous rather than fibrous

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45
Q

What does the conjunctiva do?

A

It is a mucus membrane lining of space inside palpebral fissure (except cornea) provides moist smooth surface for movements of globes and lids; moisture in eye and much of immune competency of external eye

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46
Q

Conjunctiva histology

A

Non-keritanized stratified squamous to columnar epithelium with goblet cells; gradually blends into stratified squamous epithelium of corneal surface at limbus and eyelid skin at lid margins

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47
Q

Membrana nictitans

A

Aka nicitating membrane, police semilunaris, or third eyelid; this is fold of conjunctiva ventromedial to eye

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48
Q

Conjunctival sac

A

Potential space inside closed eyelids

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49
Q

Divisions of conjunctiva

A

All continuous one to the other (and continuous at the limbus with the non-keritanized stratified squamous anterior corneal epithelium);

  1. Palpebreal or tarsal conjunctiva
  2. Bulbar conjunctiva
  3. Conjunctiva covering third eyelid bulbar and palpebral surfaces
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50
Q

Palpebral conjunctiva

A

Ie tarsal conjunctiva; thick, dark pink in color, small vessels visible, lines entire inner surface of eyelids from lid margin 360 degrees continuing to forbid where it turns and reflects onto the globe

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51
Q

Fornix

A

Approximately at the level of the orbital rim; transitional area between palpebral and bulbar conjunctiva in recess of conjunctival sac

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52
Q

Bulbar conjunctiva

A

Thin, colorless,and transparent with few vessels normally visible; may be partially pigmented in some breeds especially temporarily

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53
Q

Sclera visibility

A

Visible through transparent conjunctiva

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54
Q

Third eyelid conjunctiva

A

Bulbar surface covered in bulbar nictans conjunctival surface and palpebral surface covered in palpebreal surface of the nicitans

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55
Q

Conjunctiva heavily invested with ___

A

Goblet cells and numerous lymphatic aggregates may be present within submucosa of conjunctiva

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56
Q

Deep to conjunctiva

A

Bulbar sheath (ie tennon’s capsule) (loose connective tissue); attaches conjunctiva to globe, facilitates expensive free movement of eyeball and has many immune compentent cells that secrete immune surveillance (mast cells, eosinophils, macrophages, and lymphocytes)

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57
Q

Membrana nictians

A

Fold of conjunctiva from ventromedial fornix supported with t shaped hyaline cartilage, horizontal part keeps cornea clean and shaping tear film, free edge usually pigmented in dogs, almost completely hidden from view in proper position

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58
Q

What surrounds stem of t shaped hyaline cartilage

A

Seromucoid, superfical gland of third eyelid; ductules from this gland open onto bulbar surface of nicitans in region of lymph follicles found there in submucosa of conjunctiva

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59
Q

Movement of nictians

A

Highly mobile, can cover entire cornea; movement is primarily passive; can be active movement in cats and birds

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60
Q

Third eyelid retraction

A

Facilitated by postganglionic sympathetic fibers from cranial cervical ganglion

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61
Q

Horner’s syndrome

A

Loss of sympathetic innervation anywhere along path to eye leads to prolapse of nictitans, enophthalmos, meiosis, ptosis and reddened conjunctiva

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62
Q

Equine chronic ocular irritation

A

Can be with or without an ulcer, caused because horse has a pocket or crypt of conjunctiava centrally on bulbar suface that can trap foreign material, insects ect.

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63
Q

Is the nicitans a vestigial structure?

A

NO it is an essential component of a healthy eye in most domestic species

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64
Q

Prefrontal tear film

A

Keeps cornea constantly and uniformly moist; prevents desication and consequently keritanization opacification and even loss of anterior epithelium of the cornea

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65
Q

Loss of anterior epithelium of cornea

A

Corneal ulcer

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66
Q

Lacrimal apparatus

A

Encompassing term for all of the structures responsible for production, dispersal, and drainage of tears

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67
Q

Tri-laminar tear film

A
  1. Superfical layer
  2. Middle (aqueous layer)
  3. Inner mucus (mucin) layer
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68
Q

Superfical layer of tear film

A

Sebaceous (oily), from tarsal (meiboman gland); prevents evaporation and overflow of tear film

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69
Q

Middle aqueous layer of tear film

A

2 main sources in dog

  1. Lacrimal gland- seromucoid gland, located dorsolaterally under zygomatic process of frontal bone within lamina of periorbita (contributes 60-70% of total tear production); secretions enter the dorsotemporal conjunctival sac via many tiny ductules
  2. Superfical gland of their eyelid (or nictitans gland)- also sromucoid in dog, empties onto bulbar surface of nictans
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70
Q

Innervation of lacrimal gland

A

Responses to parasympathetic stimulus via CN VII

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71
Q

Inner mucus (mucin) layer of tear film

A

Produced by conjunctival goblet cells which are concentrated in fornicles of conjunctiva

72
Q

Tear flow

A

Tears spread across cornea via blinking, surface tension, and eye movements

73
Q

Blinking

A

Tears pumped medially toward lacrimal lake
tears sucked into tiny lacrimal puncta via negative pressure
Tears enter lacrimal canaliculi
Then enter the lacrimal sac located in a fossa in lacrimal bone
Then travel via nasolacrimal duct through maxillary bone and sinus to drain in nasal passage via nasolacrimal origice

74
Q

Keratoconjunctivitis Sicca

A

Insufficient tears or dry eye

75
Q

Lacrimation

A

Overproduction of tears (usually reflex secretions associated with pain or inflammation)

76
Q

Epiphora

A

Overflow of tears due to obstruction (anatomical, functional, disease)

77
Q

Intraocular muscles

A

Muscles inside eye that control pupil, lens, and facilitate drainage of fluid from inside eye

78
Q

Extraocluar muscles

A

Striated muscles with in periorbita with tendenenous attachments to sclera that facial tears movements of eyes
Rectus muscles: dorsal lateral ventral medial
Oblique muscles: dorsal and ventral
Retractor bulbi: cone of muscle fibers surrounding optic nerve (deep to rectus); attach globe caudal to recti

79
Q

Tenon’s capsule or fascia bulbi

A

Surrounds extrinsic ocular muscles and the glob from limbus to optic nerve, loose elastic like connective tissue network; facilitates smooth ocular movements

80
Q

Extraocular muscle function

A

3 opposing pairs of muscles rotate eye around 3 axes

81
Q

Anterior axis

A

Anterior to posterior- (cornea to optic nerve); oblique muscles rotate the eye around the A-P axis and retractors move eye along this axis

82
Q

Medial axis

A

Medial to lateral axis; lateral equator to medial equator; dorsal and ventral rectus

83
Q

Dorsal axis

A

Dorsal to ventral axis dorsal equator to ventral equator; medial and lateral rectus

84
Q

Dorsal

A

Superior

85
Q

Ventral

A

Inferior

86
Q

Strabismus

A

Deviation of eye; if inactivity of one muscle eye will deviate toward active muscle

87
Q

Lateral rectus and retrobulbar innervation

A

Cranial nerve VI (abducens nerve) (LR6)

88
Q

Dorsal oblique

A

Ie superior oblique= cranial nerve IV (trochlear nerve) (SO4)

89
Q

Extraocular muscle innervation

A

LR6SO4

All other extraocular muscles innervated by cranial nerve III

90
Q

All other extraocular muscle innervation

A

Via cranial nerve III

91
Q

Down and out ventrolateral strabismus

A

Seen with cranial nerve III paralysis; dorsal oblique muscle in dogs attaches posterior to equator of globe so when III not functioning unopposed function of DO results in ventral globe deviation

92
Q

What cranial nerves have ocular significance

A

II,III, IV, V, VI, and VII

93
Q

CN II

A

Optic nerve; formed by axons leaving retinal ganglion cells; considered extension or brain and part of CNS

94
Q

CN III

A

Oculomotor nerve; provides most of ocular motor function via innervation DR, MR, VR, VO and levator palpebrae superioris; carries preganglionic parasympathetic fibers to the cillia Ray ganglion (for constriction of pupil sphincters and ciliary muscles); controls inwards and upwards movements of eyes

95
Q

CN VI

A

Trochlear nerve; innervates DO

96
Q

CN V

A

Trigeminal nerve
3 main branches
1. V1- ophthalmic branch (somatic afferent from eye and medial canthal skin); carries potsganglionic sympathetic fibers to the eye
2. V2- maxillary branch, carries SE from lateral canthus
3. V3- mandibular branch; innervates temporalis and masseter muscles

97
Q

CN VI

A

Abducens or abducent nerve; innervates LR and RB muscles

98
Q

CN VII

A

Facial nerve; innervates orbicularis oculi muscle (eyelid closer); parasympathetic fibers to lacrimal gland travel with CN VII

99
Q

Arterial supply to eye

A

External carotid&raquo_space; maxillary > external ophthalmic with anastomoses to internal carotid, internal opthalmic, and middle meningeal

100
Q

Venous drainage from eye

A

Primarily via facial, maxillary, and deep facial veins; much facial drainage travels through or adjacent to cavernous sinus at base of brain

101
Q

Is there a central retinal artery or vein in dogs?

A

NO; do not apply clamp to the nerve during enuclations

102
Q

Layers of globe

A

Outer ( tough fiberous tunic; cornea and sclera)
Vascular (urea= iris, cilliary body, and choroid)
Neural (retina)

103
Q

Transparent intraocular structures or fluids

A

Aqueous humor, lens, vitreous

104
Q

Internal compartments of globe

A

Anterior chamber, posterior chamber, and viterous chamber/ vitreous compartment

105
Q

Anterior and posterior chambers

A

Contain aqueous humor, transparent almost cell free and protein free fluid that bathes lens iris and corneal endothelium

106
Q

Vitreous or vitreal humor

A

Transparent composed of intricately arranged collagenous fibrils forming gel like substance that fills majority of posterior portion of eye posterior to lens; secreted in part by retina, embryonic ocular vasculartur, and by lens; serves many functions such as helping to maintain retina in position

107
Q

Outer tunic

A

Cornea and sclera

108
Q

Cornea

A

Transparent anterior portion of fibrous tunic of eye; .6-.8mm thick, 15-30% globe area; main refractive surface of eye

109
Q

Limbus

A

Location of cornea blending seamlessly into sclera

110
Q

Why is corneal transparency maintained?

A

Normal cornea is moist
avascular non-keritanized, and non-pigmented epithelium
uniform size and precise arrangement of Type I collagen
In relatively dehydrated state
Has small non-myelinated nerve fibers

111
Q

Corneal nutrition

A

Occurs via diffusion from sclera vessels near limbus, from tear film, from serous humor; if any of these are abnormal or altered disease will result

112
Q

Layers of the cornea

A

4 histological, 5 functional layers

113
Q

Histological layers of cornea

A

Anterior epithelium, stroma, descemet’s membrane, posterior epithelium (corneal endothelium)

114
Q

Functional layers of the cornea

A

Tear film (WILL NOT SHOW UP ON HISTO SECTION)
Anterior epithelium
Stroma
Descemet’s membrane
Posterior epithelium (corneal endothelium)

115
Q

Anterior epithelium

A

Second layer cornea, 6-8 cell layers of non keritanized stratified squamous epithelium; continuous with conjunctival epithelium; fragile and highly invested with sensory dendrites of cranial nerve V

116
Q

Stroma

A

Sometimes called substantia propria; makes up 90% corneal thickness; stromal keratocytes with GAG matrix; produce intricately and precisely arranged collagen fibrils of uniform size; alteration to this arrangement leads to cloudiness

117
Q

Descemet’s membrane

A

Modified basement membrane of posterior corneal epithelium; gets thicker throughout life

118
Q

Posterior epithelium

A

Ie corneal epithelium; critically important post-mitosis monolayer of cells that are very poorly regenerative; Na-K ATPase pump regulates nutrient diffusion into corneal stroma while pumping water out of it

119
Q

Sclera

A

Is very strong because composed of irregular arrangements, sheets and sizes of collagen; opaque white

120
Q

Lamina cribrosa

A

Sieve-like area in sclera at posterior pole of the globe where axons from retinal ganglion cells exit the globe, coalesce and form optic nerve

121
Q

Limbus

A

Junction between cornea and sclera

122
Q

Tunics of the eye

A

Outer (cornea and sclera)
Middle (Uvea)
Inner (Retina, neural)

123
Q

Uvea

A

Middle tunic of eye; aka uveal tract; vascular tunic of eye; has three continuous subdivisions (anterior to posterior- iris, ciliary body, and choroid); usually heavily pigmented in dogs

124
Q

Iris

A

Autonomically controlled diaphragm with opening in the middle (pupil) which regulates amount of light entering the eye

125
Q

Shape of pupil

A

Different in different species depending on arrangement and distribution of iris muscle fibers

126
Q

Posterior iris surface

A

Lined by two epithelial cell layers, part of sensory tunic of eye (retinal), these two layers are derived from rim of embryonic optic cup; inner layer becomes sensory retina, outer later becomes retinal pigment epithelium

127
Q

Anterior iris stroma

A

Part of posterior iris surface; this is a loose connective tissue matrix, NOT covered by an epithelium thus has a lot of texture or surface architecture

128
Q

Myoepithlial cells derived from posterior epithelium

A

Neuroectodermal in origin; form antagonistic muscles that control pupil size and shape, circular sphincter muscle and radial dilator muscle

129
Q

Circular sphincter muscle

A

Adjacent to pupil, is under parasympathetic control

130
Q

Radial dilator muscle

A

Fibers are sympathetically innervated via postganglionic fibers from cranial cervical ganglion

131
Q

Pectinate ligament

A

Attaches iris and ciliary bodies to periopheral cornea or sclera depending on species; this is located in iridocorneal angle area

132
Q

How does aqueous humor leave eye to enter trabecular meshwork

A

Mainly via fenestrations in pectinate ligament, then sclera veins back to general circulation

133
Q

Iris and lens

A

Iris rests against and conforms to curvature of the anterior lens but is not attached; anterior surface of lens is in same plan as iris

134
Q

Ciliary body

A

Circumferential Uvea continues posteriorally from iris base as ciliary body

135
Q

Ciliary processes

A

Longitudinal folds of ciliary body seen on cut section

136
Q

Cut section of ciliary body

A

Appears on cut section as pigmented thickened ridge between iris and chricoid; has longitudinal folds (ciliary processes) extending inward from it towards center of globe

137
Q

Production of aqueous humor

A

Epithelium upon ciliary process modifies blood plasma and produces aqueous humor; produced in part by diffusion and ultrafiltration but most actively facilitated by carbonic anhydride and under sympathetic and parasympathetic influences

138
Q

Aqueous humor vs plasma

A

Transparent modified plasma with increase amino acids, ascorbate, bicarbonate, CI, and decreased proteins compared to plasma

139
Q

Aqueous humor function

A

Fills anterior and posterior chambers, nuroushes and removes waste from avascular cornea and lens; maintains intraocular pressure and globe shape

140
Q

Do you visualize ciliary body during exam or normal eye

A

No

141
Q

Path of aqueous humor

A

Produced by epithets cells covering cilliary processes
Enters posterior chamber where it bathes lens
Travels through the pupillary aperture into anterior chamber
Circulates throughout anterior chamber where it bathes the corneal endothelium (via thermal currents, pupil and globe movements)
Exits eye primarily through pectinate ligament and trabecular meshowork in the iridoorneal angel (filtration angle)
Into veins in the sclera
Back to venous circulation

142
Q

Choroid

A

Posterior most extentension of vascular tunic; loose highly vascular connective tissue between sclera and retina lining entire posterior hemisphere except at optic nerve and is continuous aneriorally with cilliary body and iris

143
Q

Choroid function

A

Provides nourishment and removes waste from retina, pigment within choroid absorbs scattered light (reduces glare)

144
Q

Tapetum lucidum

A

Colorful and shiny, cellular or fibrous modification of choroid NOT separate layer (causes eye shine at night) variable size and color; usually triangular shape; found in dorsal 1/2 posterior choroid; increases reflection of light back along same path through retina to enhance low light vision

145
Q

Area of back wall of eye containing tapetum

A

Area of fungus (back of eye) containing tapetum is the tapetum fund us and remainder is non tapetum fund us

146
Q

Adult form of eye cup

A

Retina is adult form of embryonic neuroectodermal eye cup

147
Q

Neural/ retinal tunic parts

A
  1. Pars iridium retinae
  2. Pars ciliaris retinae
  3. Pars optica retinae
148
Q

Pars iridium retinae

A

Part lining the iris (part of retinal tunic); two cell layers thick; covers posterior iris and is the origin of iris musculature

149
Q

Pars ciliaris retinae

A

Part covering ciliary body (part of retinal tunic); 2 cell layers hick; inner cell layer covers ciliary process and contributes to production of aqueous humor

150
Q

Pars optica retinae

A

Visual retina; internal to the choroid; outermost layer of original optic cup forms single cell thick layer known as retinal pigment epithelium (outermost layer of mature retina)

151
Q

Derivation of 9 layers of retina internal to retinal pigment epithelium

A

Derived from inner portion of embryonic cup

152
Q

Impulses generated in rods and cones of retina

A

Travel to retinal ganglion cells; axons of ganglion cells converge at optic nerve head and penetrate sieve-like lamina cribrosa of sclera to form optic nerve; posterior cordial extensions combine with extensions form sclera to form meninges surrounding the nerve and these are continuous with meninges covering brain/ CNS

153
Q

Eye is part of CNS or PNS

A

CNS

154
Q

Lens capsule

A

Lens epithelium is on the inside basement membrane is on outside which is backwards but forms lens capsule; has elastic characteristics

155
Q

Lens

A

Biconvex posterior transparent structure immediately posterior to iris

156
Q

Zonular ligament

A

Hundreds of 2-10nm thick fibrillin rich fibers which suspend lens; circumferential attach anterior and posterior lens capsule to anterior vitreous and cilliary body

157
Q

Lens function

A

Responsible for precise focus of light on retina; responsible for the coursing power of eyes

158
Q

Accommodation

A

The variable refraction or focusing of th eye (ability of eye to increase its optical power and keep a distant object in focus as it moves closer to the eye

159
Q

Anterior lens epithelium

A

Deep to anterior lens capsule; these epithelial cells divide migrate to lens equator and elongate to form lens fibers

160
Q

Lens nucleus

A

During development posterior lens epithelium was converted to primary lens fibers these are then surrounded by secondary lens fibers forming lens nucleus

161
Q

Is there a posterior lens epithelium in the normal postnatal eye?

A

No

162
Q

Cataract

A

Any loss of transparency of the lens whether focal or diffuse

163
Q

Proteins inside lens capsule

A

Not recognized by immune system because developing lens encapsulated lens fibers before your immune system was developed so breach in lens capsule later in life exposes foreign protein immune system attacks (this is uveitis)

164
Q

Mammalian species accomidatin to near and far vision

A

Vary shape and thickness of lens (some species can move entire lens forward and back in eye)

165
Q

Resting shape of mammalian lens

A

Globoid and very thick (elasticity of lens fibers and capsule create the globoid shape)

166
Q

Maximum refracting power for lens

A

When there is no traction on it

167
Q

Globoid shape of lens in functional mammalian eye

A

Globoid shape is opposed in living functioning mammalian eye by tension of zonular fibers or ligaments attached to lens capsule near lens equator (other end of zonular fibers attaches adjacent to muscles of ciliary body; these muscles are located circumferentially around the lens)

168
Q

Circumferential cilliary muscle contraction

A

They move closer to lens relaxing zonules and lens becomes rounder and ticker facilitating near vision (increased magnification results)

169
Q

Circumferential cilary muscle relaxation

A

They move farther from the lens and the tension or pull on zolulues flattens the lends making the lens thinner and allowing focus on distant objects

170
Q

Near focusing

A

CM contract causing attached zonular fibers to relax leading to a decrease in zonule tension leading to lens returning to globoid shape for near focusing

171
Q

Far/ distance focusing

A

CM relax leading to increase zonule tension leading to lens flattens/ thins and optical strength decreases

172
Q

Aging lens

A

With age elasticity of lens is lost; hardens due to continued lens fiber growth in contained space throughout life; lens becomes flattened not globoid which means old mammals loose ability to see close objects clearly (issues with NEAR vision)

173
Q

Why does lens elasticity decrease with age

A

Because lens density increases with age; lens continually adds layers on outside just beneath capsule the center of lens eventually becomes hard as a result

174
Q

Lens hardening in humans

A

Starts around 40-45

175
Q

Lens hardening in dogs

A

Causes dogs to develop a gray appearance to their eyes, called nuclear sclerosis around age 7-8

Block One (31 decks)

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