8 – Anatomy of the Eye Flashcards
Eyes:
-where you first look
-required for survival in most species
-different in size, shape and colour between species and individuals
-similar anatomy and function
-use human anatomy DIRECTIONAL terms
Position of eyes: predatory species
-set forward
-overlapping fields of R and L view
-large field of binocular vision
-allows concentration on NEAR objects=better for depth perception for hunting
Position of eyes: prey species
-more laterally
-not much overlap between L and R field views
-have a WIDE field of view
>allows awareness of surrounding, but cost of losing binocular vision
Eye:
-globe
-bulbus oculi
Adnexa:
-structures that PROTECT and move the eyeball
>fascia
>muscles
>eyelids
>conjunctiva
>lacrimal apparatus
Orbit:
-cavity containing the EYEBALL and most of adnexa
Orbital CONE:
-adnexal structures continue in a conical shape
Periorbita:
-most external layer of orbital fascia
*connective tissue lining the orbit
Dog/cat and pig: bone of the orbit
orbit rim not fully bony
>gap completed by orbital ligament
Horse and ox: bone of the orbit
-orbital rim fully bony
Higher primates: bone of the orbit
-bones completely surround the structures posterior to the eye
Layers (tunics or coats) of the eyeball:
-made up 3 closely attached layers
>*forming a laminated sheet
Names of layers of the eyeball:
- Fibrous tunic
- Vascular tunic (uvea)
- Nervous tunic (retina)
Fibrous tunic:
-external layer
-made of dense collagenous tissue
-gives form to and protects the eyeball
-only COMPLETE tunic
Fibrous tunic includes:
-sclera
-cornea
Sclera:
-OPAQUE posterior part of the fibrous tunic
-generally white (‘white of the eye), with a bluish tinge
>some species grayish due to pigments
Cornea:
-rostral ¼ of fibrous tunic
-bulges out
-avascular
>fed by diffusion
-interstitial fluid constantly pumped out to help transparency
Cornea made of:
-special DENSE connective tissue arranged in lamellar form
-lots of nerve endings
Nerve endings of cornea:
-make it sensitive to touch
Ex. corneal reflex checked under anesthesia
Corneoscleral junction (limbus):
-where the sclera and cornea come together
Vascular tunic (uvea):
-middle layer
-consists largely of blood vessels and SMOOTH MUSCLE
Role of vascular tunic:
-nourish
-regulate lens shape and size of pupil
Vascular tunic includes:
-choroid
-ciliary body
-iris
Choroid is:
-dense network of blood vessels within a heavily PIGMENTED connective tissue
Role of choroid:
-nourish the retina
-responsible for the ‘red eye’ in our pictures
>seeing th blood vessels
Ciliary body:
-suspends lens
-regulates curvature of lens
-production of aqueous humor
Iris:
-SUSPENDED between cornea and lens
-only internal structure seen through cornea without instruments
-FLAT RING attached at periphery to sclera
*adjusts size of pupil=controls amount of light coming in
Iris shape:
may change among species/individuals
Iris colour:
-determines ‘colour of the eye’
-most melanin=dark brown
-albino eyes have no melanin=appear red
-other colours are in between
Iris muscles types:
-sphincter
-dilators
Sphincter muscles of iris:
-near internal margin
Dilator muscles of iris:
-arranged radially
Pupil:
-opening in iris CENTER
-appears black because fundus is dark
Cat pupil:
-slit when constricted
-round when opens
Pupil in dog:
-round
Pupil in ox and horses:
-oval
Iridic granules:
-corpora nigra
-irregular outgrowth of posterior iris epithelium, containing COILS of capillaries
-usually seen on upper pupil margin in UNGULATES
-may provide ‘shades’
Ciliary body components:
-zonular fibers
-ciliary processes
-ciliary muscle
Zonular fibers:
-attach to the EQUATOR of the lens to suspend it
Ciliary processes:
radial ridges
-anchor for ZONULAR fibers
Ciliary muscles:
-attach ciliary processes to sclera
-smooth muscle
-used for ACCOMMODATION to focus on near/far objects
Tapetum lucidum causes:
-‘eye shine’ in animals at night
>different from red-eye in humans
What is the tapetum lucidum?
-variously coloured, light-reflected area in the dorsal fundus of the choroid
Role of tapetum lucidum:
-reflects and thus AMPLIFIES the low light at dark
-nocturnal adaptation to aid vision in dark
>humans and pigs don’t have it
Carnivores tapetum lucidum:
-CRYSTAL rods within tapetal cells are arranged so the light is split
>acting ad microscopic prisms
Herbivores tapetum lucidum:
-same results
-uses BRICKLIKE arrangement of collagen fibers
Nervous tunica (retina):
-most internal layer
-lines the choroid all the way to the margin of pupil
-responsible for vision
Nervous tunica (retina) role:
-most directly involved with vision
>converts visual signal to nerve impulses
Nervous tunica is:
-an extension of the BRAIN and connected to it by optic nerve
Optic nerve is covered by:
-meninges
Nervous tunica (retina) made of:
-largely made of NERVES
-2 layers from embryonic optic cup
>appose but not firmly attached
2 layers from embryonic optic cup names:
- Outer pigmented retina
- Inner neuroepithelial retina
Outer pigmented retina:
-firmly attached to choroid
-lacks pigment over tapetum lucidum
Inner neuroepithelial retina:
-photoreceptors (rods and cones) in CAUDAL 2/3rd of fundus
-phototransduction
2 layers appose but not firmly attached:
-inner layer kept in place by VITREOUS humor
-retinal detachment occurs and can be fused back using laser
All mammals possess:
-cones
Nocturnal species: cones
-few cones
Trichromatic vision:
-only old world higher primates
-red, green, blue
Dichromatic vision:
-most mammals
-only have 2 cone pigments with different spectra
-red/green colour blind (can see blue/yellow)
Rodents vision:
-can see ultraviolet
Our world is less colourful then:
-birds
-fish
-insects
Ocular media kinds:
-aqueous humor
-vitreous humor
Aqueous humor:
-clear fluid
>electrolytes, glucose, AA and ascorbic acid
Role of aqueous humor:
-nourish and waste removal for cornea and LENS
-maintain intraocular pressure
-transmit and refract (BEND) light
Portions of aqueous humor:
-anterior chamber: between cornea and iris
-posterior chamber: between iris and lens
Aqueous humor produced by:
-epithelial cells of ciliary body
Aqueous humor absorbed in:
-filtration (iridocorneal) angle bye venous plexus at PECTINATE LIGAMENTS
Vitreous humor:
-forms 2/3rd of eyeball volume
-gel-like (98% water, 2% collagen and hyaluronic acid)
-encapsulated in vitreous body
*CONSTANT: not normally produce/absorbed
Role of vitreous humor:
-maintain shape of eye
-maintain position of RETINA
-transmit and refract (bend) light
Lens shape:
-biconvex
-nucleus surrounded by ELASTIC fiber layers
Lens enclosed in a:
-CAPSULE
Lens suspended by:
-zonular fibers
Lens properties:
-avascular (fed by diffusion)
-dehydrated (60-75% water)
>to help with CLARITY
Lens function:
-transmit and refract (bend) light
Lens involved in:
-accommodation
Lens at rest:
-stretched out to focus on far objects (always want to be ready for danger signals)
Parasympathetic on lens:
-causes ciliary muscles to contract (collectively act as a large SPINCTER)
*relieves tension on ZONULAR FIBERS
>allows lens to become rounder to focus on near objects
Lens in older animals:
-can become CLOUDY (cataract) and less flexible (far-sighted)
