Histology of the EYe

Question 1

The Eye compartments

Answer 1

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

Question 2

eye tissues

Answer 2

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)

Question 3

Accessory Structures

Answer 3

o Conjunctiva
o Lacrimal Gland
o Eyelid

Question 4

Corneo-scleral layer: the sclera

Answer 4

 Opaque white posterior 5/6 of the eye
 Nearly avascular
 Composed of collagen and elastin

Question 5

corneo-scleral layer: the cornea

Answer 5

 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

Question 6

Refractive errors

Answer 6

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

Question 7

LASIK

Answer 7

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

Question 8

Uveal layer: the choroid

Answer 8

 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

Question 9

Uveal layer: the ciliary body

Answer 9

 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

Question 10

Functions of the ciliary body

Answer 10

accommodation
circulation of aqueous humor
corneal-irideal angle

Question 11

Accommodation

Answer 11

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

Question 12

Circulation of aqueous humor

Answer 12

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.

Question 13

Corneal-irideal angle

Answer 13

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

Question 14

Glaucoma

Answer 14

• 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

Question 15

Open-Angle Glaucoma

Answer 15

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

Question 16

Angle-Closure Glaucoma

Answer 16

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

Question 17

The Iris

Answer 17

 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

Question 18

The Lens

Answer 18

 Transparent, biconvex, and avascular
 Supported by zonule fibers making up suspensory ligaments
 Three components: lens capsule, lens epithelium, lens fibers

Question 19

Lens capsule

Answer 19

Thick, transparent basal lamina

Question 20

the lens epithelium

Answer 20

Single layer of cuboidal cells which are only present on anterior and lateral surface

Question 21

lens fibers

Answer 21

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

Question 22

Cataract

Answer 22

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