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?

One lens fiber spans from pole to pole on both equatorial sides Signup and view all the answers

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

Crystallins Signup and view all the answers

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

They elongate and transform into lens fibers Signup and view all the answers

Where does the lens bow occur within the lens structure?

As nuclei move anteriorly Signup and view all the answers

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

The outermost layer of fibers Signup and view all the answers

What happens to the lens capsule as one ages?

It becomes thicker and less elastic. Signup and view all the answers

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

Nuclear cataract Signup and view all the answers

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

They provide a suspension system for the lens. Signup and view all the answers

What is a significant consequence of posterior subcapsular cataract?

Decreases vision significantly. Signup and view all the answers

What is the primary composition of the vitreous humor?

Water, collagen, and hyaluronic acid Signup and view all the answers

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

Embryonic nucleus Signup and view all the answers

What changes occur in the lens when it is accommodated?

The diameter of the ciliary ring decreases and the lens becomes spherical. Signup and view all the answers

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

Vitreous Cortex Signup and view all the answers

What structure develops from secondary lens fibers after birth?

Adult nucleus Signup and view all the answers

How does the vitreous humor act as a shock absorber?

Through its viscoelastic properties. Signup and view all the answers

What is one of the functions of the vitreous humor?

To store metabolites for the retina and lens. Signup and view all the answers

How do lens sutures become asymmetric with age?

Due to growth of secondary lens fibers. Signup and view all the answers

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

It is anterior to the vitreous base and surrounded by the ciliary body. Signup and view all the answers

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

It decreases due to lens flattening. Signup and view all the answers

What is presbyopia related to in terms of lens changes?

Decreased ability to accommodate. Signup and view all the answers

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

Lens cortex Signup and view all the answers

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

Transmit visible light Signup and view all the answers

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

n increases from anterior surface to center Signup and view all the answers

What happens to the lens thickness as a person ages?

It increases gradually, approximately 0.023 nm/year Signup and view all the answers

What role does the lens capsule play in the eye?

Provide structure and attach zonules to the lens Signup and view all the answers

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

Refractive power steepens due to changes in lens shape Signup and view all the answers

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

By the time a person reaches 50 years old Signup and view all the answers

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

50% transmission occurs at 390nm Signup and view all the answers

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

Posterior radius of curvature: 10-15nm Signup and view all the answers

What is the strongest attachment site of the vitreous?

Vitreous base Signup and view all the answers

Which component is part of the Cloquet Canal?

Hyaloid artery Signup and view all the answers

What happens during vitreous syneresis?

Liquification and shrinking of vitreous Signup and view all the answers

Which attachment site has the weakest adhesion to the vitreous?

Retinal vessels Signup and view all the answers

The area of Martegiani is associated with which structure?

Cloquet Canal Signup and view all the answers

What is a common symptom of posterior vitreous detachment?

Flashes and floaters Signup and view all the answers

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

They are associated with the highest risk of detachment. Signup and view all the answers

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

Vitreous liquification Signup and view all the answers

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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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.