Histology of the EYe Flashcards
The Eye compartments
o Two compartments divided by the lens, suspensory ligaments and ciliary body
Anterior compartment
• Filled with aqueous humor
o Clear and watery, similar to CSF
• Contains anterior and posterior chambers separated by the iris
Posterior compartment
• Filled with vitreous humor
eye tissues
o Three tissues
Corneo-scleral layer (fibrous tunic)
• Makes up the sclera in the posterior (5/6) wall of the eye
Uveal layer (vascular tunic)
• Makes up the choroid in the posterior (5/6) wall of the eye
Retinal layer (neural tunic)
Accessory Structures
o Conjunctiva
o Lacrimal Gland
o Eyelid
Corneo-scleral layer: the sclera
Opaque white posterior 5/6 of the eye
Nearly avascular
Composed of collagen and elastin
corneo-scleral layer: the cornea
Transparent in the anterior 1/6 of the eye
Avascular but highly innervated
5 layers
• Outer epithelium
o Nonkeratinized squamous
• Bowman’s Membrane
o Thin basal lamina
• Substantia propria
o Dense collagenous tissue with sparse keratinocytes
• Descemet’s Membrane
o Thick basal lamina
• Corneal endothelium
o Responsible for active transport of fluid out of SP and allowing diffusion of metabolites from aqueous humor
Refractive errors
Myopia
Nearsightedness
Light rays are focused in front of the retina
• Cornea is too curved or
• lens is too powerful for length of globe
Hyperopia
Farsightedness
Light rays are focused behind the retina
• Lens and cornea too weak for length of globe
LASIK
o Laser assisted in-situ keratomileusis
o For both myopia and hyperopia
o Procedure:
- A corneal flap is raised using a microkeratome (About 160 microns thick)
- An ultraviolet or “cool laser” is used to ablate a precise amount of the exposed corneal stroma
- The flap is irrigated and replaced
- NO sutures are applied (The flap remains in place due to the dehydration pump action of the corneal endothelium)
- Corneal epithelial cells are replaced by mitotic cells found in the periphery, which migrate into the wound
Uveal layer: the choroid
Posterior pigmented portion of the vascular layer
Components
• Loose connective tissue
• Fibroblasts
• Melanocytes
Bruch’s Membrane
• Separates it from the retina
Choriocapillaris
• Area next to the retina, rich in capillaries
Uveal layer: the ciliary body
Forward continuation of the Uveal (vascular) layer
• Making up the Choroid in the posterior 5/6
Wedge shaped • Between the iris and vitreous body • Contains: o Loose connective tissue o Pigmented epithelium o Nonpigmented epithelium
Filtrate plasma to create aqueous humor
o Smooth Muscle
o Zonule Fibers
Radiate from ciliary processes to lens
Form suspensory ligaments of lens
Functions of the ciliary body
accommodation
circulation of aqueous humor
corneal-irideal angle
Accommodation
Ciliary Muscle Three bundles • Opens the canal of Schlemm • Two stretch the ciliary body o Occulomotor innervation o Altering the shape of the lens
Via suspensory ligaments
• As ciliary muscles contract, ciliary body stretches in length, thereby releasing tension on the suspensory ligaments
• Lens gets thicker and more convex
• Permits focus on nearby objects
Circulation of aqueous humor
o Ciliary Processes
On medial surface radiating from core
Epithelial folds with a core rich in fenestrated capillaries
Continuous production of aqueous humor
Flow:
• Enters the posterior chamber, passes through the papillary aperture between the iris and lens and enters the anterior chamber.
• Drains through the trabecular meshwork into the Canal of Schlemm and directly into venous circulation.
Corneal-irideal angle
o The area between Descemet’s membrane of the cornea and the anterior surface of the iris
o Canal of Schlemm forms a complete circle here
Glaucoma
- Refers to a group of diseases characterized by optic neuropathy resulting in loss of vision due to retinal ganglion cell death
- The number one risk factor for glaucoma is increased intraocular pressure, however, not only does high IOP not occur in all patients but management may not slow progression
Open angle vs. Angle-closure glaucoma
Open-Angle Glaucoma
o The most common form
o Corneal-irideal angle is open
o Usually presents with increased IOP (May be due to increased production or decreased outflow)
o Slow neurodegenerative process with characteristic optic nerve cupping
o Treatment
- Prostaglandins
- Beta-blockers
- Alpha adrenergic agonists
- Trabeculectomy or trabeculoplasty
Angle-Closure Glaucoma
o Corneal-irideal angle is obstructed
o Aqueous outflow is impeded
o Primary
- Unknown anatomical cause
o Secondary
- Inflammation
- Hemorrhage, neovascularization or tumor growth
o Patient may show characteristic conjunctival redness
The Iris
Colored, anterior extension of ciliary body
Controls pupillary aperture
Separates anterior and posterior chambers
Two concentric rings
• Pupillary zone (Nearest the pupil and thickest area)
• Ciliary zone (Nearest the ciliary body and widest area)
Anterior surface
• Fibroblasts and pigmented melanocytes embedded in extracellular matrix
• Eye pigmentation is determined by the number of melanocytes here
Stroma
• Well vascularized loose connective tissue with vessels arranged radially
Contractile Elements
• Myoepithelial cells making up dilator pupillae muscle (Sympathetic)
Smooth muscle cells making up sphincter pupillae muscle (Parasympathetic)
Posterior surface
• Pigmented epithelium, continuous with ciliary body
The Lens
Transparent, biconvex, and avascular
Supported by zonule fibers making up suspensory ligaments
Three components: lens capsule, lens epithelium, lens fibers
Lens capsule
Thick, transparent basal lamina
the lens epithelium
Single layer of cuboidal cells which are only present on anterior and lateral surface
lens fibers
o Around 2000 hexagonal and elongated terminally differentiated cells
o Loose nuclei and organelles during maturation
o Filled with crystallins
- Proteins that increase the refractory index of the lens
Cataract
o Leading cause of blindness in the world
o Mechanism yet unknown, but we do know:
Lens does not shed nonviable cells
Lens fibers do not have intracellular mechanism to deal with accumulation of substances
Risk factors include:
• Advanced age
• Smoking
• Sun exposure
• Alcohol consumption
• Metabolic syndrome
• Diabetes mellitus
• Malnutrition
• Inactivity
This leads us to believe the cause is photo/oxidative injury
o Currently no pharmaceuticals available
Changes in lifestyle may slow progression but damage is irreversible
o Surgical replacement with synthetic intraocular lens
Lens nucleus removed leaving lens capsule to support prosthetic
