Ophthalmology Corneal Anatomy and Astigmatism
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Questions and Answers

What is the expected central corneal thickness (pachymetry)?

  • 520 µm
  • 555 µm (correct)
  • 640 µm
  • 590 µm

Which layer of the cornea is acellular?

  • Bowman layer (correct)
  • Stroma
  • Endothelium
  • Epithelium

In with-the-rule astigmatism, where is the steepest meridian located?

  • Oblique (45º)
  • Circular (360º)
  • Horizontal (90º)
  • Vertical (180º) (correct)

Which statement correctly defines irregular astigmatism?

<p>Meridians are not 90º apart. (A)</p> Signup and view all the answers

Which of the following is a function of the corneal epithelium?

<p>Barrier against foreign invaders (C)</p> Signup and view all the answers

What is the main function of the endothelial layer of the cornea?

<p>Fluid transport to maintain transparency (D)</p> Signup and view all the answers

Which structure is responsible for maintaining the organization of the corneal stroma?

<p>Keratocytes (B)</p> Signup and view all the answers

What happens to the corneal structure with excessive hydration?

<p>Corneal swelling or edema (B)</p> Signup and view all the answers

Which of the following best describes Descemet's membrane?

<p>BM of the endothelium with elastic properties (C)</p> Signup and view all the answers

What is the primary composition of the corneal stroma?

<p>Dense, regular connective tissue (A)</p> Signup and view all the answers

What occurs during the full epithelial turnover of the cornea?

<p>Turnover occurs every 7-10 days. (A)</p> Signup and view all the answers

Which component of the cornea chiefly contributes to light transmission and transparency?

<p>Proteoglycans in the ground substance (D)</p> Signup and view all the answers

At what age does the thickness of Descemet's membrane typically double?

<p>40 years (D)</p> Signup and view all the answers

What is a primary cause of corneal edema?

<p>Too much water accumulating in corneal lamellae (A)</p> Signup and view all the answers

How does the cornea prevent infection?

<p>Due to its anti-angiogenic properties (D)</p> Signup and view all the answers

Which cranial nerve and branch provide innervation to the cornea?

<p>CN5 → Ophthalmic branch (V1) (A)</p> Signup and view all the answers

From where does the cornea primarily receive its oxygen supply?

<p>From the tear film and aqueous humor diffusion (D)</p> Signup and view all the answers

What is the function of the limbus?

<p>It is the transition zone between the cornea, conjunctiva, and sclera. (C)</p> Signup and view all the answers

What characterizes the sclera compared to the cornea?

<p>The sclera contains more collagen and fewer glycosaminoglycans. (D)</p> Signup and view all the answers

What does the term 'immune-privileged' mean in relation to the eye?

<p>It limits local immune responses to preserve vision. (C)</p> Signup and view all the answers

Where does the majority of the corneal nerves enter?

<p>At the peripheral cornea in the mid-stroma (C)</p> Signup and view all the answers

What do the palisades of Vogt consist of?

<p>Thickened epithelium with radial projections around the corneal periphery (B)</p> Signup and view all the answers

What is the primary difference between corneal and scleral permeability for drug delivery?

<p>Sclera is more permeable due to its organization and lack of tight junctions. (D)</p> Signup and view all the answers

What condition may arise from high intraocular pressure at the lamina cribrosa?

<p>Glaucoma (C)</p> Signup and view all the answers

Which layer of the eye is continuous with the cornea at the limbus?

<p>Scleral stroma (D)</p> Signup and view all the answers

What is the expected thickness of a healthy cornea?

<p>550 µm (C)</p> Signup and view all the answers

Which structure is immediately anterior to the scleral spur?

<p>Trabecular meshwork (D)</p> Signup and view all the answers

What happens to the cornea during dehydration?

<p>Increased spacing between corneal stroma (A)</p> Signup and view all the answers

What is the primary function of keratocytes within the corneal stroma?

<p>Synthesize collagen and extracellular matrix (C)</p> Signup and view all the answers

What characterizes irregular astigmatism in terms of meridian orientation?

<p>Meridians are not 90º apart (C)</p> Signup and view all the answers

Which of the following statements best describes the Bowman layer?

<p>It is an acellular layer produced before birth. (A)</p> Signup and view all the answers

In terms of corneal layers, which statement is true about the endothelium?

<p>It maintains corneal transparency through active transport. (C)</p> Signup and view all the answers

What is the expected difference in the radius of curvature between the anterior and posterior surfaces of the cornea?

<p>Posterior surface is steeper than anterior. (B)</p> Signup and view all the answers

What is a common complication associated with changes in basement membrane structure as people age?

<p>Decreased adhesion between epithelial cells and stroma (B)</p> Signup and view all the answers

Which layer of the cornea primarily plays a role in hydrating the corneal stroma?

<p>Endothelium (C)</p> Signup and view all the answers

What does 'constructive interference' imply in the context of corneal clarity?

<p>Increases light scattering and reduces transparency (D)</p> Signup and view all the answers

What is the characteristic orientation of the steepest meridian in with-the-rule astigmatism?

<p>Vertical (C)</p> Signup and view all the answers

Which component in the cornea is responsible for the ability to maintain hydration through its molecular properties?

<p>Proteoglycans (C)</p> Signup and view all the answers

What is the typical timeframe for minor superficial corneal abrasions to heal?

<p>24-48 hours (A)</p> Signup and view all the answers

In desmosomes, which property is primarily responsible for their function in corneal epithelial cells?

<p>Filament extension into the cell cytoplasm (D)</p> Signup and view all the answers

What characterizes the stroma of the cornea in terms of its structural composition?

<p>Contains organized layers of collagen fibrils (B)</p> Signup and view all the answers

What is the primary reason that the cornea does not have blood vessels?

<p>To prevent infection and inflammation (B), To maintain its transparency (C)</p> Signup and view all the answers

Where do the axons of corneal nerves primarily enter?

<p>Peripheral cornea in mid-stroma (C)</p> Signup and view all the answers

What is the function of lateral interdigitations found in the endothelium?

<p>Maintain structural integrity (A)</p> Signup and view all the answers

Which structure is most responsible for providing the cornea with nutrients during the open-eye condition?

<p>Tear film (C)</p> Signup and view all the answers

What does the term 'immune-privileged' primarily indicate in the context of the eye?

<p>The eye limits immune responses to preserve vision (A)</p> Signup and view all the answers

How does the sclera differ from the cornea in terms of permeability?

<p>The sclera is more permeable to drug delivery (C)</p> Signup and view all the answers

What characterizes the lamina cribrosa in the sclera?

<p>It is the weakest area of sclera (C)</p> Signup and view all the answers

What is the function of the palisades of Vogt in the limbus?

<p>Act as a location for stem cells (D)</p> Signup and view all the answers

What major part of the cornea transitions into the episclera at the limbus?

<p>Corneal stroma (A), Corneal epithelium (B)</p> Signup and view all the answers

Which cranial nerve is responsible for the innervation of the cornea?

<p>CN5 - Trigeminal nerve (B)</p> Signup and view all the answers

What role do the bulbar conjunctival and episcleral vessels play for the cornea?

<p>Offer nourishment via diffusion (A)</p> Signup and view all the answers

Which characteristic is true for the cornea compared to the sclera?

<p>The cornea is primarily transparent (B)</p> Signup and view all the answers

What happens to the corneal structure when it becomes excessively hydrated?

<p>It appears clouded and less organized (A)</p> Signup and view all the answers

What structural feature distinguishes the cornea from the sclera?

<p>The organization of collagen fiber arrangement (C)</p> Signup and view all the answers

What is the primary source of oxygen supply for the cornea during the open-eye condition?

<p>Tear film (D)</p> Signup and view all the answers

Which cranial nerve is responsible for innervating the cornea?

<p>CN5 (D)</p> Signup and view all the answers

What structural feature of the sclera sets it apart from the cornea?

<p>Irregular lamellae pattern (D)</p> Signup and view all the answers

What occurs to the corneal structure when it becomes excessively hydrated?

<p>Decreased spacing in corneal lamellae (A)</p> Signup and view all the answers

What defines the palisades of Vogt?

<p>Thickened epithelium with radial projections (B)</p> Signup and view all the answers

What is meant by the term 'immune-privileged' in respect to the eye?

<p>The eye limits immune responses to protect vision (B)</p> Signup and view all the answers

What happens at the lamina cribrosa during high intraocular pressure?

<p>Damage leading to loss of nerve fiber layer (B)</p> Signup and view all the answers

Where do the nerve endings of the cornea mainly reside?

<p>Intraepithelial plexus (A)</p> Signup and view all the answers

Which layer of the eye transitions into the conjunctival stroma at the limbus?

<p>Corneal stroma (A)</p> Signup and view all the answers

Which of the following best describes the blood supply to the cornea?

<p>Dependent on diffusion from tears and aqueous humor (A)</p> Signup and view all the answers

What primary characteristic differentiates the sclera from the cornea regarding drug delivery?

<p>Sclera allows faster diffusion due to fewer tight junctions (A)</p> Signup and view all the answers

What is primarily responsible for the corneal transparency?

<p>Even spacing of corneal lamellae (B)</p> Signup and view all the answers

What distinguishes the anterior scleral foramen?

<p>Connects to the cornea (A)</p> Signup and view all the answers

What constitutes the primary difference between regular and irregular astigmatism?

<p>Regular astigmatism exhibits meridians that are 90º apart. (B)</p> Signup and view all the answers

Which type of astigmatism has its steepest meridian oriented at 45º or 135º?

<p>Oblique astigmatism (D)</p> Signup and view all the answers

What is the expected average thickness of the central corneal pachymetry?

<p>555µm (B)</p> Signup and view all the answers

What role do keratocytes play within the corneal stroma?

<p>Producing collagen and extracellular matrix (D)</p> Signup and view all the answers

Which layer of the cornea is formed before birth and cannot regenerate?

<p>Bowman layer (A)</p> Signup and view all the answers

What are the components of the basement membrane in relation to the cornea?

<p>Basal lamina and reticular lamina (C)</p> Signup and view all the answers

Which structure is characterized by 'slightly leaky' intercellular junctions?

<p>Macula occludens (A)</p> Signup and view all the answers

In which layer does the majority of corneal hydration regulation occur?

<p>Endothelium (A)</p> Signup and view all the answers

What defines the term 'constructive interference' in the context of corneal clarity?

<p>Generates glare due to increased light scattering (B)</p> Signup and view all the answers

What factor primarily contributes to the corneal transparency by maintaining spacing between collagen fibrils?

<p>Glycosaminoglycans (B)</p> Signup and view all the answers

Which corneal layer's cells undergo mitosis to replenish the outer layers?

<p>Basal cells (B)</p> Signup and view all the answers

What happens to Descemet's membrane as a person ages?

<p>It thickens, doubling by approximately 40 years of age. (B)</p> Signup and view all the answers

What is the primary process responsible for the cornea's oxygen supply during the closed-eye condition?

<p>Aqueous humor diffusion (D)</p> Signup and view all the answers

Flashcards

Corneal Edema

A condition where the corneal lamellae are not evenly spaced due to excess water, causing the cornea to swell.

Stromal Plexus

A network of nerve fibers located in the corneal stroma, containing 900-1200 axons.

Intraepithelial Plexus

A network of nerve fibers located within the corneal epithelium. The myelin sheath is lost at the Bowman's layer.

Corneal Blood Supply

The cornea lacks blood vessels due to its antiangiogenic properties. Instead, it receives oxygen from the tear film and aqueous humor.

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Immune-Privileged

The eye's ability to limit local immune and inflammatory responses, preserving vision by avoiding tissue rejection.

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Limbus

The transition zone between the cornea, conjunctiva, and sclera.

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Palisades of Vogt

Thickened epithelium with radial projections around the peripheral cornea, concentrated in the superior and inferior limbus, containing stem cells.

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Sclera

The white, opaque outer layer of the eye, thicker than the cornea and composed of type I collagen in an irregular pattern.

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Scleral Foramina

Openings in the scleral tissue for passage of blood vessels and nerves.

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Lamina Cribrosa

A meshwork of scleral fibers, the weakest area of the sclera, susceptible to damage from high IOP leading to glaucoma.

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Episclera

The layer located outside the sclera and inside the conjunctiva and Tenon's capsule.

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Tenon's Capsule

A layer between the inner conjunctiva and outer episcleral tissue, surrounding and stabilizing the eyeball.

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Limbus Transition - Bowman's Layer

The Bowman's layer terminates at the limbus.

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Limbus Transition - Descemet's Membrane

The Descemet's membrane terminates at the limbus.

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Limbus Transition - Corneal Endothelium

The corneal endothelium transitions to trabecular meshwork epithelium at the limbus.

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Corneal Diameter

The measurement of the cornea's width and height. The horizontal diameter is typically 12mm, and the vertical diameter is 11mm.

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Corneal Thickness

The depth of the cornea, measured from the front surface to the back surface. The central corneal thickness is typically 540-570µm, while the peripheral thickness is larger at 710 µm.

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Corneal Radii of Curvature

The extent of the cornea's curvature, measured as the radius of a circle that would match the corneal shape. The anterior radius is about 7.8mm, and the posterior radius is smaller at 6.5mm, indicating a steeper curvature.

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With-the-Rule Astigmatism

A type of astigmatism where the steepest corneal meridian is vertical (180 degrees). This means the cornea is more curved vertically than horizontally.

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Against-the-Rule Astigmatism

A type of astigmatism where the steepest corneal meridian is horizontal (90 degrees). This means the cornea is more curved horizontally than vertically.

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Oblique Astigmatism

A type of astigmatism where the steepest corneal meridian is at an angle, either 45 degrees or 135 degrees.

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What is regular astigmatism?

Regular astigmatism is when the two main corneal meridians (steepest and flattest) are perpendicular to each other, meaning they are 90 degrees apart.

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What is irregular astigmatism?

Irregular astigmatism is when the two main corneal meridians are not perpendicular to each other, meaning they are not 90 degrees apart.

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Corneal Epithelium Layers

The outermost layer of the cornea, made of stratified, non-keratinized cells. It has three main sub-layers: surface cells, wing cells, and basal cells.

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Function of Corneal Epithelium

The corneal epithelium serves as a protective barrier, aids in corneal regeneration, and helps maintain clarity by preventing foreign particles from entering the cornea.

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Bowman's Layer

A thin, acellular layer located just below the corneal epithelium. It is a dense, irregular connective tissue that provides structural support.

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Corneal Stroma

The thickest layer of the cornea, composed of collagen fibrils, keratocytes (fibroblasts), and ground substance. It is responsible for the cornea's strength and transparency.

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Descemet's Membrane

The basement membrane of the corneal endothelium. It is a dense connective tissue that provides strength and resistance to enzymes and trauma.

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Corneal Endothelium Function

The innermost layer of the cornea, responsible for maintaining corneal clarity by regulating fluid balance and removing waste products.

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Zonula Occludens

A type of intercellular junction in the corneal epithelium, forming a tight seal to prevent foreign particles from entering.

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Desmosomes

Specialized macula adherens junctions, anchoring cells together. These junctions resist tearing of the tissue, ensuring structural integrity.

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Basement Membrane

A thin layer separating epithelium from connective tissue. It serves as an anchor for epithelial cells and has two layers: basal lamina and reticular lamina.

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Corneal Transparency

The ability of the cornea to allow light to pass through, essential for clear vision. This property is maintained by the organized structure of the stromal lamellae and proper hydration.

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Corneal Innervation

Nerve supply to the cornea, primarily from the ophthalmic branch of the trigeminal nerve (CN5). Nerves enter the cornea peripherally and form plexuses throughout its layers.

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Regular Astigmatism

Astigmatism where the two main corneal meridians (steepest and flattest) are perpendicular to each other, 90 degrees apart.

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Irregular Astigmatism

Astigmatism where the two main corneal meridians are NOT perpendicular to each other, not 90 degrees apart.

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Corneal Endothelium

The innermost layer of the cornea, responsible for maintaining corneal clarity by regulating fluid balance and removing waste.

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Corneal Epithelium Regeneration

Epithelial cells move from the inside (basal) to the outside (surface) and are shed into tears. Full turnover takes 7-10 days.

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Scattered Light

Light rays bouncing off uneven surfaces, causing glare and blurry vision.

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Anti-angiogenic Property

The cornea lacks blood vessels, preventing the growth of new blood vessels (angiogenesis). This is a key factor in its transparency and immune privilege.

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Study Notes

Normal Corneal Dimensions

  • Diameter:
    • Anterior horizontal: 12mm
    • Anterior vertical: 11mm
    • Posterior horizontal: 11.7mm
    • Circular: 11.7mm
  • Thickness:
    • Central: 540-570µm (expected 555µm)
    • Peripheral: 710µm
  • Radius of Curvature:
    • Anterior: 7.8mm
    • Posterior: 6.5mm (smaller number = steeper curvature)

Astigmatism Definitions

  • With-the-rule: Steepest meridian is vertical (180 degrees)
  • Against-the-rule: Steepest meridian is horizontal (90 degrees)
  • Oblique: Steepest meridian is 45 degrees or 135 degrees

Regular vs. Irregular Astigmatism

  • Regular: Meridional axes are 90 degrees apart
  • Irregular: Meridional axes are not 90 degrees apart

Corneal Layers and Purposes

  • Epithelium:
    • Stratified, non-keratinized cells
    • Surface, wing and basal cells
    • Bowman layer, basement membrane
    • Regeneration dependent upon cell layer
    • Nerves lose Schwann cell sheaths, pass naked into the epithelium
  • Stroma:
    • Thickest layer (~500µm)
    • Regular, dense connective tissue (Collagen fibrils, Keratocytes, ground substance)
    • Keratocytes are immune response fibroblasts (fibroblasts)

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Lecture 6: Corneal Anatomy PDF

Description

This quiz covers essential aspects of corneal dimensions, thickness, and astigmatism definitions. You'll explore the differences between regular and irregular astigmatism, as well as the various layers of the cornea and their functions. Ideal for students and professionals in ophthalmology and optometry.

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