Lens Biology and Function Quiz
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Questions and Answers

What is the primary function of the single layer of simple cuboidal epithelium on the anterior surface of the lens?

  • Transport nutrients and waste using Na+/K+ pumps (correct)
  • Secrete the posterior lens capsule throughout life
  • Form primary lens fibers during embryonic development
  • Provide structural support to the lens fibers

In which zone of the lens does cell mitosis primarily occur to generate new lens fibers?

  • Germinal/proliferative zone (correct)
  • Equatorial zone
  • Transition zone
  • Central zone

What are the structural forms that allow for the attachment of lens fibers laterally?

  • Tongue-in-groove and ball-and-socket (correct)
  • Ball-and-socket and hinge joints
  • Sutures and grooves
  • Interdigitating and overlapping connections

Which statement about lens fibers is correct?

<p>One lens fiber spans from pole to pole on both equatorial sides (C)</p> Signup and view all the answers

What is the main component of lens fibers that contributes significantly to their weight?

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

What happens to the cells in the germinal/proliferative zone as they migrate towards the equator?

<p>They elongate and transform into lens fibers (A)</p> Signup and view all the answers

Where does the lens bow occur within the lens structure?

<p>As nuclei move anteriorly (C)</p> Signup and view all the answers

Which layer of the lens is referred to as the cortex?

<p>The outermost layer of fibers (C)</p> Signup and view all the answers

What happens to the lens capsule as one ages?

<p>It becomes thicker and less elastic. (C)</p> Signup and view all the answers

Which type of cataract involves opacification in the center of the lens?

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

What is the role of the zonules in relation to the lens?

<p>They provide a suspension system for the lens. (B), They are involved in the accommodation process. (D)</p> Signup and view all the answers

What is a significant consequence of posterior subcapsular cataract?

<p>Decreases vision significantly. (C)</p> Signup and view all the answers

What is the primary composition of the vitreous humor?

<p>Water, collagen, and hyaluronic acid (D)</p> Signup and view all the answers

Which structure corresponds to the lens fibers formed during the first two months of embryonic development?

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

What changes occur in the lens when it is accommodated?

<p>The diameter of the ciliary ring decreases and the lens becomes spherical. (B)</p> Signup and view all the answers

Which zone of the vitreous is known as the outermost zone?

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

What structure develops from secondary lens fibers after birth?

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

How does the vitreous humor act as a shock absorber?

<p>Through its viscoelastic properties. (B)</p> Signup and view all the answers

What is one of the functions of the vitreous humor?

<p>To store metabolites for the retina and lens. (B)</p> Signup and view all the answers

How do lens sutures become asymmetric with age?

<p>Due to growth of secondary lens fibers. (A)</p> Signup and view all the answers

Which of the following describes the anterior cortex of the vitreous?

<p>It is anterior to the vitreous base and surrounded by the ciliary body. (B)</p> Signup and view all the answers

What happens to the refractive power of the lens during unaccommodated viewing?

<p>It decreases due to lens flattening. (D)</p> Signup and view all the answers

What is presbyopia related to in terms of lens changes?

<p>Decreased ability to accommodate. (A)</p> Signup and view all the answers

What structure is formed from epithelial cell mitosis in the germinal region of the lens?

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

What is the primary function of the lens in the eye?

<p>Transmit visible light (B)</p> Signup and view all the answers

Which characteristic best describes the gradient power index of the lens?

<p>n increases from anterior surface to center (A)</p> Signup and view all the answers

What happens to the lens thickness as a person ages?

<p>It increases gradually, approximately 0.023 nm/year (A)</p> Signup and view all the answers

What role does the lens capsule play in the eye?

<p>Provide structure and attach zonules to the lens (B)</p> Signup and view all the answers

What change occurs in the refractive power of the lens during accommodation?

<p>Refractive power steepens due to changes in lens shape (B)</p> Signup and view all the answers

At what age does the amplitude of accommodation generally tend to decrease towards 0D?

<p>By the time a person reaches 50 years old (C)</p> Signup and view all the answers

Which of the following statements about the uv radiation filtering capacity of the lens is correct?

<p>50% transmission occurs at 390nm (C)</p> Signup and view all the answers

Which of the following is NOT a normal dimension of the lens?

<p>Posterior radius of curvature: 10-15nm (D)</p> Signup and view all the answers

What is the strongest attachment site of the vitreous?

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

Which component is part of the Cloquet Canal?

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

What happens during vitreous syneresis?

<p>Liquification and shrinking of vitreous (B)</p> Signup and view all the answers

Which attachment site has the weakest adhesion to the vitreous?

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

The area of Martegiani is associated with which structure?

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

What is a common symptom of posterior vitreous detachment?

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

Which statement accurately describes the retinal vessels' attachment to the vitreous?

<p>They are associated with the highest risk of detachment. (D)</p> Signup and view all the answers

What change commonly occurs in the vitreous as a person ages?

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

Flashcards

Lens Function: Light Transmission

The lens transmits visible light, allowing it to reach the retina at the back of the eye.

Lens Function: Refraction

The lens refracts (bends) light, focusing it onto the retina for sharp vision.

Lens: Malleable & Refractive Power

The lens is flexible, allowing it to change shape and adjust its refractive power to focus on objects at different distances.

Lens: UV Filter

The lens absorbs harmful ultraviolet (UV) radiation from sunlight, protecting the eye from damage.

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Lens: Dimensions

The lens is biconvex (curved on both sides), with a steeper posterior surface than the anterior surface. Its thickness increases with age, and its diameter grows throughout life.

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Lens: Accommodative Power

The lens's refractive power is higher at the center than at the edges. This gradient helps focus light.

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Lens: Accommodation

Accommodation is the process of changing the lens shape to focus on near or far objects. The lens becomes rounder for near vision, flatter for far vision.

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Lens Layers: Capsule

The capsule is the outermost layer, transparent, and acellular. It provides structural support and allows zonules to attach to the lens.

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Lens Epithelium

A single layer of simple cuboidal epithelium covering the anterior surface of the lens. It's responsible for generating new lens fibers and secreting the anterior lens capsule.

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Lens Fiber Formation

New lens fibers are formed from cells in the germinal zone of the lens epithelium. These cells migrate towards the equator, elongate, and differentiate into lens fibers.

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Lens Zones

The lens epithelium is organized into different zones: the central zone (flattened cells), the germinal zone (columnar cells), and the transition zone and equator (elongating cells).

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Lens Capsule

A transparent basement membrane that surrounds the entire lens. It's secreted by the lens epithelium and helps maintain the lens's shape.

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Lens Fibers

Long, elongated cells that make up the bulk of the lens. They are filled with crystallins, proteins that help focus light.

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Lens Sutures

The points where lens fibers meet, forming a complex pattern. They are important for maintaining the lens's structure and allowing for smooth movement.

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Zonules

Fine, delicate fibers that attach the lens to the ciliary body. They are responsible for adjusting the lens's shape for near and far vision.

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Lens and Zonules Relationship

The zonules connect the lens to the ciliary body, allowing for changes in lens shape and focusing. This is essential for clear vision.

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Lens Capsule Function

The lens capsule is the outermost layer of the lens, providing structural support and acting as an attachment point for the zonules. It also helps mold the lens shape for accommodation.

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Zonules: Lens Suspension

Zonules are tiny fibers that attach to the lens capsule and the ciliary body. They act like a suspension system, holding the lens in place and enabling shape changes during accommodation.

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Embryonic Nucleus: Lens Core

The embryonic nucleus is the innermost, densest part of the lens. It forms during early development and has the highest refractive index.

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Fetal Nucleus: Lens Growth

This layer develops around the embryonic nucleus during fetal development. It grows through the addition of secondary lens fibers, merging at Y-shaped sutures.

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Adult Nucleus: Mature Lens

This layer forms after birth and continues to grow until sexual maturity. Its fibers create the adult lens structure with stellate sutures.

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Lens Cortex: Outer Layer

The lens cortex is the outermost layer, formed by secondary lens fibers from the epithelial layer. It continues growing throughout life, providing ongoing lens development.

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Accommodation Steps: Unaccommodated

When viewing distant objects, the ciliary muscle relaxes, the ciliary ring stretches, and the lens flattens due to zonule tension.

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Accommodation Steps: Accommodated

When viewing near objects, blue light stimulates retinal cones, causing the ciliary muscle to contract. This reduces zonule tension, allowing the lens to round and increase its dioptric power.

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Presbyopia

Reduced ability of the lens to focus on near objects with age. This is due to age-related changes in the lens capsule, nucleus, and zonular fibers.

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Cloquet's Canal

A channel running through the center of the vitreous, remnant of the hyaloid artery and primary vitreous. It starts at the anterior cortex and ends at the Area of Martegiani.

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Lens Capsule Changes with Age

The lens capsule, the outermost layer of the lens, becomes thicker and less elastic with age. This contributes to presbyopia, as the lens is less able to change shape for near vision.

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Vitreous Base

The strongest attachment site of the vitreous to the eye. Located at the pars plana and peripheral retina, containing dense collagen network.

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Lens Nucleus Changes with Age

The lens nucleus, the central core of the lens, becomes more rigid with age. This also contributes to presbyopia, as the lens becomes less flexible.

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Posterior Lens Attachment

Attachment between the posterior lens and anterior vitreous. It's called the 'retrolental ligament of Wieger'.

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Optic Disc Attachment

A circular attachment surrounding the optic disc. Weakens with age.

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Anterior Lens Shift

With age, the lens shifts slightly forward. This increases tension on the zonular fibers, making it more difficult for the lens to accommodate for near vision, contributing to presbyopia.

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Cataracts

Opacification (clouding) of the lens. This can occur in different parts of the lens, leading to blurry or distorted vision.

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Macular Attachment

An annular area of adhesion around the macula. Called the 'vitreomacular adhesion'.

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Retinal Vessel Attachment

The weakest attachment site where vitreous strands extend and attach to blood vessels.

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Nuclear Cataracts

Cataracts that form in the lens nucleus. These are often a natural consequence of aging.

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Cortical Cataracts

Cataracts that form in the lens cortex (outer layer). These appear as spoke-like patterns extending from the periphery towards the center of the lens.

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Vitreous Syneresis

Liquification and rearrangement of collagen fibers in the vitreous, leading to shrinkage.

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Posterior Subcapsular Cataracts

Cataracts that develop beneath the posterior capsule of the lens. They can severely impair vision as they block the line of sight.

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Posterior Vitreous Detachment (PVD)

Separation of the posterior vitreous cortex from the internal limiting membrane (ILM). Common in the elderly.

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Study Notes

Lens Functions

  • Transmits visible light
  • Refracts and focuses light onto the retina
  • Variable refractive power (contributes to total eye power)
  • Main UV light filter
  • 50% transmission at 390nm, 0% at 360nm

Lens Dimensions

  • Shape: Biconvex
  • Anterior radius of curvature: 8-14nm
  • Posterior radius of curvature: 5-8nm
  • Poles: 3.5-5mm thick
  • Lens thickness increases with age (0.023nm/year)
  • Lens diameter: 6.5mm at birth, 10mm in adults
  • Equator: Largest lens circumference

Lens Accommodation

  • Power index increases from anterior to center
  • Index of refraction decreases from center to posterior
  • Higher crystallin concentration = higher refractive index
  • Accommodation increases refractive power (steepening of surfaces)
  • Amplitude decreases with age (14D at 8-12 years to 0D at 50 years)

Lens Layers

  • Capsule:
    • Outermost layer
    • Transparent and acellular
    • Modified basement membrane
    • Provides structure, zonules attach
    • Collagen type IV
    • Thicker where zonules attach, thinnest posteriorly
  • Epithelium:
    • Anterior surface only
    • Single layer, simple cuboidal
    • Metabolically active
    • Responsible for lens capsule secretion

Lens Fiber

  • Innermost layers
  • Cortex (outer) and Nucleus (inner)
  • Fibers extend pole-to-pole
  • Sutures form where fibers meet
  • Junctions (ball-and-socket) allow movement
  • Crystallins make up ~40% of fiber weight

Vitreous Functions

  • Mechanical support for surrounding tissues
  • Shock absorber (viscoelastic)
  • Protects retina during movement
  • Transmits and refracts light
  • Storage area for metabolites

Vitreous Composition

  • 98-99% water
  • Collagen type II
  • Hyaluronic acid
  • Salts, soluble proteins, glucose, lactic acid, and ions

Vitreous Zones

  • Vitreous Cortex (outer)
  • Outermost zone/hyaloid surface
  • Anterior and posterior cortex
  • Surrounded by the ciliary body, posterior chamber, lens

Lens Divisions

  • Embryonic Nucleus: Primary lens fibers, first 2-8 months (highest index of refraction)
  • Fetal Nucleus: Secondary lens fibers, grow around embryonic nucleus
  • Adult Nucleus: From secondary fibers; birth to sexual maturity, stellate sutures.

Vitreous Attachment Sights

  • Vitreous base: Attachment to ciliary body (pars plana) and peripheral retina (ILM), strong collagen network
  • Optic Disc: Peripapillary circular adhesion (strength decreases with age)
  • Macula: Annular adhesion (ring attachment), retinal vessels (weakest)

Vitreous Changes with Age

  • Vitreous syneresis: Liquification and rearrangement of collagen fibres
  • Increased risk of retinal detachment
  • Posterior Vitreous Detachment (separation of posterior vitreal cortex from ILM)
  • Common in elderly; 50% symptomatic by 50

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Lecture 8: Lens Anatomy & Physiology PDF

Description

Test your knowledge on the structure and function of the eye lens. This quiz covers lens dimensions, accommodation, and the various layers of the lens. Perfect for students studying eye anatomy or physiology.

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