May: Eye Histo Flashcards
What is the gross organization of the outer (supporting) layer (tunica fibrosa)?
- Sclera
a. white, opaque
b. posterior 5/6th of eye - Cornea
a. primary light refractor
b. transparent
c. anterior 1/6th eye - Limbus: corneal-scleral junction
- Conjunctiva
What is the gross organization of the middle layer-Uvea (tunica vasculosa)?
- Vascular layer
- Components
a. choroid - posterior 2/3rds of uvea
b. ciliary body (cont. of 2a)
c. ciliary processes (part of 2b)
d. iris (anterior continuation of 2a)
• pigmented - lightproofs the eyes, reduces reflection.
What is the gross organization of the inner layer-Retina (tunica nervosa)?
- Layers: (X2)
a. pigmented layer
b. sensory layer - Ora Serrata
a. sensory layer ends: become a non-pigmented layer of cells
b. pigmented and non-pigmented layers continue. - Optic Disc - “blind spot”
- Fovea Centralis - maximal visual acuity
What are the other major structures of the eye?
- Lens - secondary light refractor
- Zonules (ligaments of Zinn)
• extend from ciliary processes and inserts into lens
• fibrillin fibers - Pupil
- Conjunctiva
a. mucous membrane
b. covers inner eye lid (palpebral conjunc.) and exposed part of anterior sclera
(bulbar conjunc.)
Where are the chambers? What are their contents?
Anterior - between cornea and iris Posterior - between iris and lens Vitreous - posterior to lens 2. Contents: a. anterior and posterior chambers 1) aqueous humor 2) watery, rich in proteins, essentially an ultrafiltrate of blood. (similar to tissue fluid) b. vitreous chamber 1) vitreous humor 2) 99% water and 1% glycosaminoglycans (mainly hyaluronic acid)
What does the cornea do?
§ primary refractor of light § avascular and transparent 1. Size a. about 0.5mm thick in central zone b. a little thicker at periphery.
What are the regions (5) of the retina?
a. surface epithelium
1) stratified squamous (non-keratinized) epithelium
2) continuous with epithelium of bulbar conjunctiva
3
b. Bowman’s membrane
1) thickened basal lamina of 2a above
2) somewhat resistant to bacterial invasion
3) does not regenerate
c. substantia propria
1) dense, regular connective tissue
2) constitutes about 90% of corneal thickness
3) several layers of collagen fibers; each layer cross at an angle to each
other.
4) fibrocytes present
d. Descemet’s membrane - basal lamina of corneal endothelium.
e. corneal endothelium - simple squamous epithelium.
What is the innervation of the retina? What is it’s nutrition and elimination?
- Innervation-pain type nerve endings in epithelium (nociceptors). Stimulation results in blink reflex and flow of tears.
- Nutrition and Elimination:
a. cornea is avascular
b. nutrients from peripheral vessels and anterior chamber diffuse through corneal matrix
c. CO2 eliminated through corneal epithelium
What is the sclera?
- General
a. white in color
b. consists of dense irregular connective tissue
c. posteriorly, outer part of sclera continues with dura and arachnoid layers of
meninges; innermost part of sclera continues with pia mater.
d. Opacity of sclera as compared with cornea is due to its greater water content. - Vascularity
a. poorly supplied with blood vessels
b. many larger vessels pierce it obliquely to gain access to middle layer (Uvea) - Lamina cribosa: perforations in sclera allowing passage of fibers forming optic
nerve. - Limbus - transition between cornea and sclera
- Canal of Schlemm
a. located at limbus
b. drains fluid from anterior chamber
c. canal communicates with venous system
What is the choroid coat of the uvea?
- Choroid coat
a. 0.1-0.2 mm thick
b. contains blood vessels for retinal nourishment
c. layers
1) Epichoroid
• outer layer
• chiefly elastic fibers
• some pigmented cells present
2) choriocapillaris
• rich in small blood vessels
• damage to these vessels results in retinal damage
d. Bruch’s membrane
1) basement membrane-like structure
2) firmly attaches retina to choriocapillaris
3) extends from ora serrata to optic disk
What is the ciliary body and processes of the uvea?
a. anterior expansion of the choroid at the level of the lens
b. contains smooth muscle that is involved with accommodation
c. ciliary processes
1) extensions of the ciliary body
2) contains a core of loose conn. tissue
d. epithelial lining - two layers of epithelium
• superficial layer of unpigmented cells; also called ciliary epithelium
• deep layer of pigmented cells (contains melanin)
e. aqueous humor
1) secreted by ciliary epithelium into posterior chamber
2) basically an ultrafiltrate of blood
3) passes into anterior chamber
4) enters trabecular meshwork at limbus (spaces of Fontana)
5) enters canal of Schlemm
6) canal of Schlemm is drained by local veins
f. glaucoma
1) increase in intraocular pressure
2) can occur if drainage of aqueous humor is impeded
What is the iris of the uvea?
a. anterior extension of ciliary body
b. anterior iris lined by a single layer of cells that is continuous with the corneal
endothelium
c. posterior iris lined by 2 layers of epithelium continuous with that lining the
ciliary body and processes
d. core of iris:
1) loose connective tissue
2) contain melanocytes - eye color in part due to density of melanin
3) blood vessels present
4) smooth muscle bundles
§ sphinctor pupillae
• circularly arranged
• located near pupil
• parasympathetic innervation
§ dilator pupillae
• radially arranged
• sympathetic innervation
What is the lens?
- Biconvex in shape
- High degree of elasticity which decreases with age
- Attached to ciliary processes by zonules (ligaments of Zinn)
What are the components of the lens?
a. Lens Capsule
1) homogenous-appearing material surrounding outermost part of the lens
2) 10-20 μm thick
3) contains collagen and amorphous glycoproteins
b. subcapsular epithelium
1) single layer of cuboidal cells
2) present only on the anterior surface of lens
c. lens fibers
1) comprises the bulk of the lens
2) highly differentiated elongated cells adhered by gap junctions
3) cells lose nuclei during differentiation
4) cells are hexagonal in cross-section
What is the function of the lens?
a. secondary refractor of light
b. functions in adjustment of light refraction for near & far vision (focusing).
1) object at a distance:
• ciliary muscle relaxed
• tension on zonules
• lens stretched and at a minimum curvature
2) object near:
• ciliary muscle contracted
• tension on zonules is reduced
• lens curvature increased
c. cataracts = lens opacity
