BMS302 Lecture 1: Eye Structure

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Questions and Answers

Which of the following accurately describes the outer fibrous supporting layer of the eye?

It contains the sclera and iris, with the sclera being the most anterior part.

It includes both the cornea and sclera, with the cornea being the transparent portion. (correct)

It consists of the cornea and sclera, with the cornea being the denser part.

It is composed of the cornea and choroid, where the choroid is non-vascular.

Which chamber of the eye is located between the lens and the posterior surface of the iris?

Accessory chamber

Vitreous chamber

Posterior chamber (correct)

Anterior chamber

What is the primary function of the vitreous body in the eye?

To facilitate light refraction through the eye

To support the structure of the cornea

To absorb excess light to prevent glare

To maintain the shape of the eye and protect the retina (correct)

Which layer of the eye contains the outer retinal pigment epithelium and the inner neural retina?

Inner sensory layer Signup and view all the answers

What structure connects the lens to the ciliary body in the eye?

Zonular fibers Signup and view all the answers

What is the primary role of the basal layer of the corneal epithelium?

Undergoes mitosis to regenerate the epithelium Signup and view all the answers

Bowman's membrane is primarily characterized by which of the following features?

It serves as a protective barrier against trauma Signup and view all the answers

Which statement best describes the stromal layer of the cornea?

It contains approximately 60 layers of parallel collagen fibrils Signup and view all the answers

How does Bowman's membrane heal after injury?

By the formation of scar tissue made of collagen Signup and view all the answers

What is the composition of the collagen fibrils in the stroma?

They are arranged at right angles to adjacent lamellae Signup and view all the answers

What is the main role of Descemet’s endothelium in the cornea?

To pump Na+ and maintain hydration Signup and view all the answers

Which component is NOT involved in the transparency of the cornea?

Presence of vascular supply Signup and view all the answers

How does the cornea primarily receive its nutrients?

From the aqueous humor and limbal vessels Signup and view all the answers

What characterizes the composition of Descemet’s membrane?

A thick basal lamina with a collagen fiber network Signup and view all the answers

Which of the following is true about corneal corpuscles?

They consist of regular collagen lamellae and fibroblasts Signup and view all the answers

Why does damage to Descemet’s endothelium lead to corneal swelling?

It impairs Na+ pumping and fluid balance Signup and view all the answers

What surgical procedure involves changing the curvature of the cornea?

LASIK surgery Signup and view all the answers

What is the primary reason for the cornea's optimal light refraction?

Regular arrangement of its components Signup and view all the answers

What is a key characteristic of corneal transplantation?

Frequently meets with success Signup and view all the answers

Study Notes

Course Information

Course: BMS302
Lecture: 1
Topic: Eye
Instructor: Dr. Manal Shaaban Hafez
Institution: Galala University
Semester: Fall 2024

Intended Learning Outcomes

List the three coats of the eye
Determine the eye chambers
Describe the structure and correlated function of the cornea
Describe the structure and correlated function of the sclera
Determine the structural changes at the corneoscleral junction and its importance

Eye Ball Structure

Fibrous Tunic:
- Sclera (opaque, posterior 5/6 of the fibrous coat)
- Cornea (transparent, anterior 1/6)
Vascular Tunic
- Choroid (melanocytes, macrophages and connective tissue)
- Ciliary body
- Iris
Sensory Tunic / Inner Layer
- Retina (Pigmented + Neural)

Layers of Eye Ball

1-Outer fibrous supporting layer:
- A-Cornea (anterior transparent 1/6)
- B-Sclera (posterior dense opaque 5/6)
2-Middle vascular layer (uveal layer)
- A-Choroid
- B-Ciliary body (contains ciliary muscle, ciliary processes and zonular fibers)
- C-Iris (contains pupil, sphincte pupillae and dilator pupillae)
3-Inner sensory layer:
- A. Outer retinal pigment epithelium
- B. Inner neural retina

Eye Chambers

1- Anterior chamber: Filled with aqueous humor, between cornea and anterior surface of the iris.
2- Posterior chamber: Filled with aqueous humor, between posterior surface of iris and lens. The lens is a transparent biconvex structure attached to the ciliary body by zonular fibers.
3- Vitreous chamber: Filled with vitreous body (a gel-like substance), behind the lens and surrounded by the retina.

Cornea Structure

Anterior 1/6 of the fibrous coat
Transparent and avascular
Highly innervated
Thin in center (0.5 mm)
Thick in periphery (1 mm)
Five layers: epithelium, Bowman's membrane, stroma, Descemet's membrane, endothelium

Corneal Epithelium

Stratified squamous, non-keratinized epithelium
Adheres by desmosomes
5-6 layers thick, resting on a thick basement membrane (8-12 µm)
Superficial cells have microvilli to keep the cornea wet
Intermediate cells are polygonal and have free nerve endings
Basal layer is cuboidal, has high regenerative power by mitosis

Bowman's Membrane

Thick, homogenous, non-cellular layer
Basement membrane of the stratified epithelium
Synthesized by corneal epithelium and stromal cells
Protective barrier against mechanical injuries and bacterial invasion
Does not regenerate, heals by fibrous tissue, causing corneal opacities
Ends abruptly at the corneoscleral limbus

Stroma (Substantia Propria)

Thickest layer (90%)
Non-vascular
Regular lamellae of parallel collagen fibrils (arranged at right angles)
Fibroblasts and keratocytes are arranged in rows
Immersed in ground substance (proteoglycans)
Maintains collagen lamella organization and spacing

Descemet's Membrane

Homogeneous, thick basal lamina
Formed from collagen fibers by the underlying endothelial cells
Continuously synthesized by the underlying endothelium
Readily regenerates after injury

Descemet's Endothelium

Simple squamous cells lining the inner surface
Active in protein synthesis & maintains the basement membrane
Responsible for Na+ pumping, water removal to maintain corneal hydration & transparency
Contains pinocytotic vesicles (maintain optimal light refraction)
Metabolic exchange between cornea and aqueous humor
Damage leads to corneal swelling

Corneal Nutrition

Receives nutrition from aqueous humor (center)
Receives nutrition from vessels in the limbus (periphery)
Receives oxygen from the atmosphere.

Corneal Transparency

Lacks vascular & lymphatic drainage
Regular arrangement of components
Similar refractive indices of components
Continuous fluid withdrawal from the stroma.

Medical Applications

Corneal transplantation
LASIK surgery (for myopia, hyperopia, astigmatism)
Physical or metabolic damage to endothelial cells can lead to rapid corneal swelling, which can result in corneal opacity.

Conjunctiva

Thin, transparent mucosa
Bulbar conjunctiva: covers exposed sclera
Palpebral conjunctiva: lines internal surface of eyelids
Stratified columnar epithelium (goblet cells present)
Loose connective tissue (lymphocytes, macrophages)

Conjunctiva Functions

Lubrication & protection
Defense (immune response)
Drainage of aqueous humor

Corneo-scleral Junction (Limbus)

Transition zone between cornea and sclera
Transparent corneal stroma merges with the opaque sclera
Limbus is highly vascularized, provides metabolites to corneal cells by diffusion
It contains the trabecular meshwork, Canal of Schlemm, and important stem cells for corneal maintenance.
Critical elements for drainage of aqueous humor

Importance of Limbus

Basal epithelial layer contains stem cells for corneal maintenance
Stem cells at limbus creates a conjunctival barrier
Trabecular meshwork and Canal of Schlemm drain aqueous humor

Histological Changes of Corneoscleral Junction (Limbus)

Corneal epithelium thickens, continuous with bulbar conjunctiva
Bowman's membrane ends and is replaced by subconjunctival supportive tissue
Stroma becomes sclera with less regular collagen bundles
Consists of a circular Canal of Schlemm

Descemet's Membrane in Corneoscleral Junction

Descemet's membrane splits to form trabecular meshwork
Descemet's endothelium lines trabecular meshwork and canal of Schlemm
Canal of Schlemm and trabecular meshwork are located in the iridocorneal angle.

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Description

Test your knowledge on the structure of the eye as covered in BMS302 by Dr. Manal Shaaban Hafez. This quiz will focus on the three coats of the eye, the chambers, and the functions of crucial parts like the cornea and sclera. Get ready to delve into the fascinating anatomy of the eye!