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FRCOphth part 1 Anatomy Eyeball > Lens > Flashcards

Lens Flashcards

pg 179-186

1
Q

What is hypermetropia?

A

A condition where the eyeball is too short or the lens is not strong enough, causing difficulty in focusing on near objects

Also known as farsightedness

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2
Q

How can hypermetropia be corrected?

A

By placing a convex lens in front of the eye

This is typically done using eyeglasses

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3
Q

What happens to light rays in hypermetropia?

A

They fall behind the retina

This occurs because the lens cannot sufficiently bend the light rays

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4
Q

What is myopia?

A

A condition where the eyeball is too long or the lens is too strong, causing difficulty in focusing on distant objects

Also known as nearsightedness

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5
Q

How can myopia be corrected?

A

By placing a concave lens in front of the eye

This diverges the light rays

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6
Q

What happens to light rays in myopia?

A

They fall in front of the retina

This occurs because the image cannot be focused properly on the retina

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7
Q

What is presbyopia?

A

A condition caused by the loss of lens elasticity with age, leading to difficulty in focusing on near objects

It primarily affects older individuals

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8
Q

What corrective lenses are often used for presbyopia?

A

Bifocal glasses

The upper part is for distant vision, while the lower part is for near vision

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9
Q

What is the primary issue with the lens in presbyopia?

A

The lens cannot assume a spherical shape

This affects the ability to accommodate for near vision

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10
Q

In what condition is a person unable to focus on a near object?

A

Hypermetropia

This results in the need for accommodation to see distant objects clearly

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11
Q

In what condition is a person unable to see a distant object clearly?

A

Myopia

This occurs because the image is focused in front of the retina

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12
Q

What happens to the nucleus of the lens with increasing age?

A

It becomes sclerosed and yellowish

The increasing refractive index compensates for the flattening of the lens, but increased density reduces visual acuity.

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13
Q

What is a cataract?

A

A condition where the lens becomes opaque

Senile cataract is the most common form and must be distinguished from nuclear sclerosis.

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14
Q

What is the cause of senile cataract?

A

Not known

It is characterized by the accumulation of metabolic products and osmotic balance disturbance.

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15
Q

What are other forms of cataract besides senile cataract?

A

Congenital cataracts, cataracts associated with intraocular diseases, ocular trauma, and systemic diseases

Examples of systemic diseases include diabetes mellitus and scleroderma.

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16
Q

What is the most commonly performed type of cataract surgery?

A

Phacoemulsification

This procedure involves breaking up the dense nucleus of the lens using ultrasound.

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17
Q

Describe the phacoemulsification procedure.

A

The dense nucleus is emulsified and removed by vacuum

Various methods exist for breaking up the lens, including dividing it into pieces.

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18
Q

What is the ‘phaco chop’ technique?

A

A method that splits the lens along its fracture lines using pressure from a cleaving instrument

This technique can be applied from the front or back of the lens.

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19
Q

Why is knowledge of the lens capsule important in cataract surgery?

A

It helps in understanding its consistency, dimensions, and ability to stretch for intraocular lens insertion

The resilient nature allows for capsulorrhexis procedures.

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20
Q

What is capsulorrhexis?

A

The careful removal of a circular piece of the anterior wall of the lens capsule

If done without tearing, it can be safely dilated for lens insertion.

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21
Q

What happens to the lens capsule after the removal of lens substance in adults?

A

It collapses and its diameter increases to approximately 9.5 to 10.5 mm

After implantation, it assumes an oval shape.

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22
Q

What is the maximum equatorial diameter of the lens capsule after lens insertion?

A

12.0 mm

The introduction of a lens can stretch the equator from approximately 10.5 mm to 11.9 mm.

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23
Q

True or False: The equatorial diameter can exceed 12.0 mm if the capsule remains intact.

A

False

The intact capsule cannot stretch beyond this measurement.

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24
Q

What happens to lens fiber cells during development?

A

They lose their nuclei and cytoplasmic organelles become specialized for the production of lens proteins known as crystallins.

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25
Q

What are the two types of crystallins found in the lens?

A
  • Alpha
  • Beta
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26
Q

What percentage of the lens fiber mass do crystallins constitute?

A

Up to 60 percent.

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27
Q

What causes the high refractive index of the lens?

A

The presence of crystallins.

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28
Q

What compensates for spherical and chromatic aberrations in the lens?

A

Differing concentrations of crystallins in different parts of the lens.

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29
Q

How do lens epithelial cells and lens fibers relate to each other?

A

They interdigitate and have numerous gap junctions, making the lens act like a syncytium.

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30
Q

What is the suspensory ligament of the lens also known as?

A

Zonule.

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31
Q

Where do zonule fibers arise from?

A

The epithelium of the ciliary processes.

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32
Q

How many bundles do the zonule fibers form?

A

About 140 bundles.

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33
Q

What shape does the elastic lens capsule tend to assume when the eye is at rest?

A

A discoid shape.

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34
Q

What is the role of the ciliary muscle in accommodation?

A

It contracts to allow the lens to assume a more globular shape for focusing on close objects.

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35
Q

What happens to the pupil during accommodation?

A

It becomes smaller.

36
Q

What condition is characterized by a decreased ability to accommodate due to lens changes with age?

A

Presbyopia.

37
Q

How does the lens change with advancing age?

A

It becomes denser and less elastic.

38
Q

What happens to the central portion of the lens as new lens fibers are added throughout life?

A

It becomes less pliable and more compact.

39
Q

How much larger is the lens in a 65-year-old compared to a 25-year-old?

A

One-third larger.

40
Q

Where do lens epithelial cells transform into lens fibers?

A

At the equator

This is where lens mitotic activity is at a maximum.

41
Q

What are the two main functions of the lens epithelium?

A
  • Actively dividing and differentiating into lens cell fibers
  • Transporting substances from the aqueous humor to the lens interior and secreting capsular material
42
Q

What is the primary mass of the lens composed of?

A

Lens fibers

These fibers are formed by the multiplication and differentiation of lens epithelial cells.

43
Q

Describe the structure of a lens fiber.

A

A hexagonal prism in cross-section and very long, measuring about 10 mm

44
Q

How do lens fibers run in the lens?

A

Meridionally from the posterior to the anterior lens surface; they are U-shaped

45
Q

What are the two types of sutures formed by opposing lens fibers?

A
  • Anterior suture: erect Y shape
  • Posterior suture: inverted Y shape
46
Q

What term is used to describe the earliest fiber mass in the center of the lens?

A

Embryonic nucleus

This is followed by the fetal nucleus and the adult nucleus.

47
Q

What is the area surrounding the adult nucleus called?

A

Lens cortex

48
Q

What components can be found in the cytoplasm of lens fibers?

A
  • Small vesicles
  • Microfilaments
  • Microtubules
  • Occasional mitochondrion
49
Q

How are lens fibers held together?

A

By interlocking adjacent plasma membranes

50
Q

What type of interdigitation occurs between lens fibers?

A
  • Tongue-and-groove
  • Ball-and-socket
51
Q

True or False: Interdigitations in the superficial zones of the lens are more complicated.

A

False

52
Q

What may explain how deep lens fibers can survive away from a source of nourishment?

A

Numerous gap junctions

53
Q

The process of lens cell elongation results in the movement of the nucleus. Where does the nucleus move as fibers pass deeper?

A

Anteriorly, taking a position anterior to the nuclei of more superficial cells

54
Q

Fill in the blank: The continuous production of lens fibers leads to progressively more complicated _______ patterns.

A

Suture

55
Q

What happens to the nucleus of a lens fiber as it elongates?

A

The nucleus remains intact initially but later fragments and disappears

56
Q

What happens to the size of the adult nucleus over time?

A

It is always increasing

57
Q

What are zonular fibers?

A

Fibers that connect the lens to the ciliary processes

58
Q

What is the function of the lens capsule?

A

Serves as a diffusion barrier and molds the shape of the lens during accommodation

59
Q

What types of compounds can the lens capsule diffuse?

A

Low-molecular-weight compounds

60
Q

What does the lens capsule restrict?

A

Movement of large colloidal particles

61
Q

Describe the lens epithelium.

A

Cuboidal and lies beneath the capsule, found only on the anterior surface

62
Q

What happens to lens epithelial cells at the equator?

A

They elongate and form columnar cells arranged in meridional rows

63
Q

The lens capsule is freely permeable to _______.

A

[low-molecular-weight compounds]

64
Q

The chief function of the lens capsule is to _______.

A

[mold the shape of the lens]

65
Q

True or False: The lens epithelium is found on the posterior surface of the lens.

A

False

66
Q

What shape do lens epithelial cells take on the anterior surface?

A

Cuboidal

67
Q

What are the refractive media of the eye?

A

The cornea, the aqueous humor, the lens, and the vitreous body

68
Q

Where is the lens situated in the eye?

A

Behind the iris and the pupil, in front of the vitreous body

69
Q

What shape does the lens have?

A

Transparent, biconvex structure

70
Q

What is the measurement of the lens in adults?

A

Approximately 10 mm in diameter and 4 mm thick

71
Q

What are the anterior and posterior poles of the lens?

A

Center points on its anterior and posterior surfaces

72
Q

What forms the axis of the lens?

A

A line joining the anterior and posterior poles

73
Q

What is the equator of the lens?

A

The marginal circumference of the lens

74
Q

What keeps the lens in position?

A

Suspensory ligaments

75
Q

What is the dioptric power of the entire eye?

A

About 58 diopters

76
Q

How much dioptric power does the lens contribute?

A

About 15 diopters

77
Q

How does the lens change its dioptric power?

A

By changing its shape to focus on distant and near objects

78
Q

What happens to the range of dioptric power with age?

A

It is reduced, about 8 diopters by age 40 and 1 to 2 diopters by age 60

79
Q

What is the refractive index of the lens in the periphery and inner zone?

A

About 1.36 in the periphery and 1.4 in the inner zone

80
Q

How does the lens grow throughout life?

A

It continues to grow, measuring about 6.5 mm at birth and 10 mm in adulthood

81
Q

What are the three parts of the lens?

A
  • Elastic capsule
  • Lens epithelium
  • Lens fibers
82
Q

What is the function of the elastic capsule of the lens?

A

It envelops the entire lens

83
Q

Where is the capsule thickest and thinnest?

A

Thickest near the equator (about 20 um) and thinnest at the posterior pole (about 3 um)

84
Q

What does the inner surface of the anterior part of the capsule contact?

A

The lens epithelium

85
Q

How does the capsule appear under light and electron microscopes?

A

Homogeneous under light microscope; consists of 40 lamellae under electron microscope

86
Q

What is the composition of each lamella in the capsule?

A

Type IV collagen fibrils embedded in a matrix of glycoproteins and sulfonated glycosaminoglycan

87
Q

How much can the elastic capsule be stretched without tearing?

A

Up to about 60 percent of its circumference

FRCOphth part 1 Anatomy Eyeball (10 decks)

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