Eye Flashcards
Eye
Photosensitive organ that permits vision and color discrimination
Has a protective reflex (blinks when something moves towards it)
Where is the eye located?
Lies in the orbit
Protected by bone laterally and caudally
What are the 3 layers (tunics) of the eyeball?
- Fibrous (1/5 cornea, 4/5 sclera)
- Vascular (choroid, ciliary body, iris)
- Nervous (retina- pars optica and para caeca)
What does the Pars caeca include?
Blind area:
1. Pars ciliaris (Pigments epith. covering ciliary body)
2. Pars iridica (pigmented epith. covering the iris)
Refractive parts of the eye
Cornea
Aqueous humor
Lens
Vitreous Body
Opaque Parts of the Eye
Iris
Ciliary body
Choroid
What are the 2 compartments of the eye?
- Anterior compartment
- Posterior compartment
Anterior Compartment
Filled with aqueous humor and located between the cornea and lens
Has 2 chambers; anterior and posterior
Anterior and Posterior Chambers
Ant: cornea, lens and iris
Post: iris, lens and ciliary bodies
Filled with aqueous humor
Posterior Compartment
Between the lens and the retina and filled with vitreous humor
The ________ leaves at the optic disc (fundus)
Optic nerve
Aqueous Humor
Produced as filtrate of the blood
Like blood plasma but poor in proteins
Provides oxygen and nutrients to intraocular structures
How does aqueous humor move throughout the eye?
Formed in ciliary process –> posteror chamber –> anterior chamber via pupil –> spaces of Fontana @ cornea-iris junction –> absorbed into general circulation (Canal of Schelumm)
Function of the cornea-iris junction
Drains aqueous humor from anterior chamber
Canal of Schlemm
Cornea-scleral junction
Absent in domestic animals
Cornea
Forms rostral boundary of anterior chamber, transparent, devoid of BVs
Limbus
Cornea-sclera junction
Site of BVs supplying nutrients via diffusion
What are the 5 layers of the cornea?
- Stratified squamous non-keratin (outer)
- Bowman’s membrane (BM)
- Substantia propria (stroma, collagen)
- Descemet’s membrane
- Simple squamous epith. (mitochondria and active pinocytosis)
Significance of substantia propria
Thickest layer
Collagen fibers and fibrocytes arranged in right angles
What does epithelium of the cornea do?
Actively move water out of the stroma
Sclera
Outermost layer
DRCT
Site of attachment of eye extrinsic muscles
Choroid
Vascular layer between sclera and retina
Dark layer with melanocytes
What are the layers of choroid?
- Suprachoroid
- Vascular
- Taptum lucidum
- Choriocapillary
- Bruch’s membrane
How is the Tapetum lucidum is different species?
Cellular in dogs and cats
Fibrous in ruminants and horses
Absent in pigs
Iris
Controls the amount of light entering the eye via smooth muscles:
Sphincter/constrictor: parasym
Radial Dilator: sympathetic
Structure of the iris
Anterior surface: simple squamous
Core: CT, Bvs and melanocytes
Muscles
Post. surface: bilaminar cuboidal (pars iridica of the retina)
Iris muscles are _________ in avian
Striated
Ciliary processes
Irregular projections where zonular fibers attach to the lens
Covered with bilateral cuboidal (non pigmented and pigmented layer)
Ciliary muscles
Parasympathetic which function in visual accommodation by changing the shape of the lens
Lens
Lens capsule- collagen IV, simple cuboidal
Lens epithelium- anterior surface
Lens fibers- acellular
How are lens fibers formed?
By differentiation and elongation of epithelial cells at the equator of the lens
Lose elasticity and plasticity with age
Vitreous body
“Gel” filled posterior compartment
99% water and 1 % hyaluronic acid (GAGs)
Retina
2 portions: Pars ceca and Pars optica
Pars ceca
Non-sensory
Covers ciliary body and iris
Continuation of the pigmented layer of the retina
Pars optica
Sensory with 10 layers
- Outer nuclear layer (nuclei of rods and cones)*
- Inner Nuclear layer (bipolar) *
- Ganglion layer *
- Optical nerve fiber layer (multipolar gang) *
How does light pass through the retina?
Passes all layers to activate rods and cones –> pigments convert energy in AP –> carried via neuronal connections to the optic nerve
Pigment epithelium
Squamous to cuboidal
Microvillous processes, melanin
Transfers nutrients from choriocapillary layer to the rods and cones, phagocytosis/ recycling of segments of photoreceptor cells and absorption of light
Rods
Human eye has 120 million
Rhodopsin pigment
Sensitive to light and suited for dim light vision
Cones
Human eye has 5 million
Iodopsin pigment
Suited for day light and color discrimination
Macula (fovea) have the highest concentration of cones
What clin sigs are for the cornea?
Epithelium heal via mitosis
Transplant possible
Dehydration causes corneal opacities
Descemetocele (increased ocular pressure)
Glaucoma
Increased intraocular pressure
Usually due to blockage in drainage of aqueous humor
What clin sigs are for the lens?
Lens hardens with age (less elasticity)
Vacuolation
Precipitation of proteins results in cataracts
What clin sigs are for the iris/ pupil?
Lesion of sympathetic nerve supply –> Horner’s syndrome
Miosis enophthalmos (sunken eyeball)
Ptosis (drooping eyelid)
Mydriasis (from parasym. damage, dilated pupil)
Detached Retina
Separation occurs between the pigmented layer of the retina and layer of the rods/cones
Reason for detached retina?
Develops from a bilayer “cup”
Outer layer differentiates into non neural pigmented layer
Inner layer differentiates into nervous layers of the retina
Causing space between cup layers
