Tag: Anatomy & Physiology Of Lens

Anatomy & Physiology Of Lens

ANATOMY & PHYSIOLOGY OF LENS

Q. 1

Which of the following does not handle free radicals in the lens of the eye?

 A

Vit. A

 B

Vit. C

 C

Vic. E

 D

Catalase

Q. 1

Which of the following does not handle free radicals in the lens of the eye?

 A

Vit. A

 B

Vit. C

 C

Vic. E

 D

Catalase

Ans. A

Explanation:

Proteins in the lens are unusually long lived and are thus subject to extensive and accumulated oxidative damage. The damaged proteins accumulate, aggregate, and precipitate; causing the lens to loose its transparency.

Of critical importance is the decrease in the Na+/K+ ATPase, resulting in the inability to maintain steady concentrations of Na+, K+, and Ca++within the lens. The decreased activity of this enzyme is thought to be associated with oxidative damage to the sulfhydryl portions of the molecule, usually protected by the interaction of several antioxidants, especially glutathione (GSH), ascorbate, superoxide, dismutase (SOD), and catalase. Like the processes leading to ARMD, senile cataracts are the result of years of damage and accumulated oxidation. Several reviews are available that discuss the relationship between cataracts and oxidative damage.
Antioxidants in the eye
  • Ascorbate (Vitamin C)
  • Catalase
  • Superoxide dysmutase (SOD)
  • Glutathione (GSH)
  • d-alpha-tocoferol (Vit E)
  • Lipoic acid
  • Microelements required : Zn, Cu and Mn
  • Carotene
  • Ubiquinone 
Ginko biloba extract is known to be anti-oxidant. Free radicals are highly reactive molecular species with an unpaired electron. They can react with, and modify, proteins, nucleic acids and fatty acids in cell membranes and plasma lipoproteins.
Radical damage to lipids and proteins in plasma lipoproteins is a factor in the development of atherosclerosis and coronary artery disease; radical damage to nucleic acids may induce heritable mutations and cancer; radical damage to proteins may lead to the development of autoimmune diseases.
Ref: Bender D.A. (2011). Chapter 45. Free Radicals and Antioxidant Nutrients. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.

Q. 2

True statement about crystalline lens:

 A

Fibres of fetal nucleus meet around sutures

 B

Lamellar cataract is the most common type of congenital cataract

 C

In Blue dot cataract vision is severely impaired

 D

a and b

Q. 2

True statement about crystalline lens:

 A

Fibres of fetal nucleus meet around sutures

 B

Lamellar cataract is the most common type of congenital cataract

 C

In Blue dot cataract vision is severely impaired

 D

a and b

Ans. D

Explanation:

A, B i.e. Fibres of fetal nucleus meet around sutures; Lamellar cataract is the most common type of congenital cataract


Q. 3

Diameter of an adult crystalline lens is:

 A

5-6 mm

 B

7-8 mm

 C

9-10 mm

 D

11-12 mm

Q. 3

Diameter of an adult crystalline lens is:

 A

5-6 mm

 B

7-8 mm

 C

9-10 mm

 D

11-12 mm

Ans. C

Explanation:

Ans. 11-12 mm

Quiz In Between


Q. 4

Thickness of the adult crystalline lens is about:

 A

2.5 mm

 B

3.5 mm

 C

4.25 mm

 D

5 mm

Q. 4

Thickness of the adult crystalline lens is about:

 A

2.5 mm

 B

3.5 mm

 C

4.25 mm

 D

5 mm

Ans. D

Explanation:

Ans. 5 mm


Q. 5

Infantile nucleus of the crystalline lens refers to the nucleus developed from:

 A

3 months of gestation to till birth

 B

Birth to one year of age

 C

Birth to puberty

 D

One year of age to 3 years of age

Q. 5

Infantile nucleus of the crystalline lens refers to the nucleus developed from:

 A

3 months of gestation to till birth

 B

Birth to one year of age

 C

Birth to puberty

 D

One year of age to 3 years of age

Ans. C

Explanation:

Ans. Birth to puberty


Q. 6

The lens fibres meet around the Y-shaped sutures in which part of nucleus of the crystalline lens:

 A

Embryonic nucleus

 B

Fetal nucleus

 C

Infantile nucleus

 D

All of the above

Q. 6

The lens fibres meet around the Y-shaped sutures in which part of nucleus of the crystalline lens:

 A

Embryonic nucleus

 B

Fetal nucleus

 C

Infantile nucleus

 D

All of the above

Ans. A

Explanation:

Ans. Embryonic nucleus

Quiz In Between


Q. 7

The youngest lens fibres are present in:

 A

Central core of the lens nucleus

 B

Outer layer of the nucleus

 C

Deeper layer of the cortex

 D

Superficial layer of the cortex

Q. 7

The youngest lens fibres are present in:

 A

Central core of the lens nucleus

 B

Outer layer of the nucleus

 C

Deeper layer of the cortex

 D

Superficial layer of the cortex

Ans. D

Explanation:

Ans. Superficial layer of the cortex


Q. 8

Crystalline lens absorbs light rays shorter than:

 A

295 rim

 B

350 nm

 C

390 nm

 D

490 nm

Q. 8

Crystalline lens absorbs light rays shorter than:

 A

295 rim

 B

350 nm

 C

390 nm

 D

490 nm

Ans. B

Explanation:

Ans. 350 nm


Q. 9

Lens has a respiratory quotient of:

 A

1

 B

0.6

 C

0.7

 D

0.9

Q. 9

Lens has a respiratory quotient of:

 A

1

 B

0.6

 C

0.7

 D

0.9

Ans. A

Explanation:

Ans. 1

Quiz In Between


Q. 10

The capsule of the crystalline lens is thinnest at:

 A

Anterior pole

 B

Posterior pole

 C

Equator

 D

None

Q. 10

The capsule of the crystalline lens is thinnest at:

 A

Anterior pole

 B

Posterior pole

 C

Equator

 D

None

Ans. B

Explanation:

Ans. Posterior pole

Lens capsule:

  • Thickest at pre- equator region & thinnest at the posterior pole.

Q. 11

The crystalline lens derives its nourishment from:

 A

Blood vessels

 B

Connective tissue

 C

Aqueous and vitreous

 D

Zonules

Q. 11

The crystalline lens derives its nourishment from:

 A

Blood vessels

 B

Connective tissue

 C

Aqueous and vitreous

 D

Zonules

Ans. C

Explanation:

Ans. Aqueous and vitreous


Q. 12

Lens develops from:               

September 2012

 A

Neural crest

 B

Mesoderm

 C

Neuroectoderm

 D

Surface ectoderm

Q. 12

Lens develops from:               

September 2012

 A

Neural crest

 B

Mesoderm

 C

Neuroectoderm

 D

Surface ectoderm

Ans. D

Explanation:

Ans. D i.e. Surface ectoderm

Embryology of eyeball

  • Structures derived from mesoderm:
  • Corneal stroma & endothelium,
  • Only smooth muscles of iris,
  • All muscles (EXCEPT iris muscle)
  • Structures derived from surface ectoderm:
  • Conjunctival epithelium,
  • Lens

Structures derived from neuroectoderm:

  • Epithelium of iris & ciliary body,
  • Muscles of iris (constrictor & dilator pupillae)

Quiz In Between


Q. 13

Crystalline lens develops from ‑

 A

Mesoderm

 B

Endoderm

 C

Surface ectoderm

 D

Neuroectoderm

Q. 13

Crystalline lens develops from ‑

 A

Mesoderm

 B

Endoderm

 C

Surface ectoderm

 D

Neuroectoderm

Ans. C

Explanation:

Ans. is ‘c’ i.e., Surface ectoderm


Q. 14

Oldest lens fibres are found in ‑

 A

Capsule

 B

Cortex

 C

Cortex

 D

Nucleus

Q. 14

Oldest lens fibres are found in ‑

 A

Capsule

 B

Cortex

 C

Cortex

 D

Nucleus

Ans. D

Explanation:

Ans. is ‘d’ i.e., Nucleus

Anatomy of crystalline lens

  • There are three structural elements that make up lens ‑

1) Lens capsule

  • A transparent membrane surrounding the lens like a pocket. It is thicker over the anterior surface than the posterior surface. It is thickest at pre- equator region and thinnest at the posterior pole. When an artificial lens replaces the natural lens in cataract surgery (IOL implantation), it is placed in this same capsule.

2) Lens epithelium

  • It is a single layer on the anterior (front) surface of the lens. There is no epithelium on posterior surface. The epithelial cells distribute fluid, ion and glucose through the entire lens. They also create new fibers throughout a person’s life.

3) Lens fibres

  • These are long protein fibers that are closely packed and parallel. They make up most of the lens volume and are laid horizontally, front to back, and concentrically like layers of an onion.As the lens fibres are formed throughout the life, these are arranged compactly as nucleus and cortex of the lens.

a) Nucleus : – It is the central part containing the oldest fibres. it consists of different zones :-

  1. Embryonic nucleus :- Formed at 1-3 months of gestation, therefore consists the oldest primary fibres.
  2. Fetal nucleus :- Lies around the embryonic nucleus and is formed from 3 months of gestation till birth.
  3. Infantile nucleus :- Corresponding the lens from birth to puberty and surrounds the fetal nucleus.
  4. Adults :- Corresponds to the lens fibres formed after puberty to rest of the life.

b) Cortex :- It is the peripheral part containg the youngest fibres.

  • The ciliary zonules (Zonules of zinn or suspensory ligaments of lens) hold the lens in position and enable the ciliary muscle to act on it. These consist essentially of a series of fibres which run from the ciliary body and fuse into the outer layer of the lens capsule around the equatorial zone.

Q. 15

Focal length of 0.25 m power of lens is ‑

 A

40 D

 B

1/4 D

 C

4 D

 D

25 D

Q. 15

Focal length of 0.25 m power of lens is ‑

 A

40 D

 B

1/4 D

 C

4 D

 D

25 D

Ans. C

Explanation:

Ans. is ‘c’ i.e., 4 D

  • Power of a lens (P) is defined as the ability of the lens to converge a beam of light falling on the lens. o For a converging (convex) lens the power is taken as positive and for a diverging (concave) ? ens power is taken as negative.
  • It is measured as reciprocal of the focal length in metres i.e. P = 1/f. The unit of power is dioptre (D). One dioptre is the power of a lens of focal length one metre.
  • Therefore,Power of lens = 1/f = 1/0.25 = 4D
  • Thus, A lens with a focal length of 0.25 m will be four times as strong as one with a focal length of 1 m: the refractive power of such a lens is therefore 4 dioptres (4 D).

Quiz In Between


Q. 16

Water content in lens is ‑

 A

64%

 B

35%

 C

1%

 D

28%

Q. 16

Water content in lens is ‑

 A

64%

 B

35%

 C

1%

 D

28%

Ans. A

Explanation:

Ans. is ‘a’ i.e., 64%

The lens is composed of 64% water, 35% protein, and 1% lipid, carbohydrate and trace elements. The protein concentration in the lens is actually the highest amongst body tissues. The main types of proteins are alpha (31%), beta (55%) and gamma (2%) crystallins, and insoluble albuminoids (12%).


Q. 17

Epithelium is absent in lens on ‑

 A

Anterior surface

 B

Anterior pole

 C

Posterior surface

 D

At zonular attachment

Q. 17

Epithelium is absent in lens on ‑

 A

Anterior surface

 B

Anterior pole

 C

Posterior surface

 D

At zonular attachment

Ans. C

Explanation:

Ans. is ‘c’ i.e., Posterior surface

Anatomy of crystalline lens

  • There are three structural elements that make up lens –

1. Lens capsule

 A transparent membrane surrounding the lens like a pocket. It is thicker over the anterior surface than the posterior surface. It is thickest at pre- equator region and thinnest at the posterior pole. When an artificial lens replaces the natural lens in cataract surgery (IOL implantation), it is placed in this same capsule.

2. Lens epithelium

It is a single layer on the anterior (front) surface of the lens. There is no epithelium on posterior surface. The epithelial cells distribute fluid, ion and glucose through the entire lens. They also create new fibers through­out a person’s life.

3. Lens fibres

These are long protein fibers that arc closely packed and parallel. They make up most of the lens volume and are laid horizontally, front to back, and concentrically like layers of an onion.As the lens fibres are formed throughout the life, these are arranged compactly as nucleus and cortex of the lens.

a) Nucleus : – It is the central part containing the oldest fibres. it consists of different zones :-

  1. Embryonic nucleus :- Formed at 1-3 months of gestation, therefore consists the oldest primary fibres.
  2. Fetal nucleus : – Lies around the embryonic nucleus and is formed from 3 months of gestation till birth.
  3. Infantile nucleus :- Corresponding the lens from birth to puberty and surrounds the fetal nucleus.
  4. Adults :- Corresponds to the lens fibres formed after puberty to rest of the life.
  5. Cortex :- It is the peripheral part containg the youngest fibres.
  • The ciliary zonules (Zonules of zinn or suspensory ligaments of lens) hold the lens in position and enable the ciliary muscle to act on it. These consist essentially of a series of fibres which run from the ciliary body and fuse into the outer layer of the lens capsule around the equatorial zone.

Quiz In Between



Anatomy & Physiology Of Lens

ANATOMY & PHYSIOLOGY OF LENS


ANATOMY & PHYSIOLOGY OF LENS

  • Lens is a transparent, bi-convex, crystalline structure 
  • Placed b/w iris & the vitreous in a saucer shaped depression called patellar fossa.
  • Its equatorial diameter is 10 mm.
  • Refractive index is 1.39.
  • Total power is 15-16 D.

ANATOMY OF CRYSTALLINE LENS

  • There are 3 structural elements that make up lens-

1) Lens capsule:

  • Thickest at pre- equator region & thinnest at the posterior pole.
  • Hyaloideocapsular ligament of Weiger or retrolental ligament is a strong adhesion b/w the lens & posterior capsule.
  • It is a circular adhesion 8-9 mm in diameter.
  • This attachment is termed as Egger’s line.
  • Within this circle is a potential space called as Space of Burger or Erggelet’s space.

2) Lens epithelium :

  • Single layer on the anterior (front) surface of the lens.
  • There is no epithelium on posterior surface.

3) Lens fibres 

  • These are long protein fibers that are closely packed & parallel.
  • Lens fibres are formed through out the life, these are arranged compactly as nucleus and cortex of the lens.

a) Nucleus : It is the central part containing the oldest fibres. Consists of different zones:

  1. Embryonic nucleus: Formed at 1-3 months of gestation, therefore consists the oldest primary fibres.
  2. Fetal nucleus : Lies around the embryonic nucleus & is formed from 3 months of gestation till birth.
  3. Infantile nucleus: Corresponding the lens from birth to puberty & surrounds the fetal nucleus.
  4. Adults: Corresponds to the lens fibres formed after puberty to rest of the life.

b) Cortex: It is the peripheral part contain the youngest fibres.

  • The ciliary zonules (Zonules of zinn or suspensory ligaments of ligaments of lens) hold the lens in position & enable the ciliary muscle to act on it.

Fibres of zonules are divided into:

1) Hayloid zonule (orbiculo-posterior capsular fibres)

  • These originate from the pars plana of the ciliary body & inser into the capsule just posterior to the equator at the edge of patellar fossa.

2) Anterior zonule (orbiculo-anterior capsular fibres or  anterior zonular sheet)

  • These originate from the pars plana of the ciliary body & insert into the capsule just anterior to the equator.
  • These are the strongest & thickest of the zonular fibres.

3) Posterior zonule (ciliary-posterior capsular fibres or posterior zonular sheet)

  • These originate from the pars plicate of the ciliary body & insert into the capsule posterior to equator.
  • These are most numerous.

4) Equatorial zonule (Cilio-equatorial fibres)

  • These originate from the pars plicata of ciliary body & insert into the lens capsule at the equator.

Metabolic activity of lens

  • Lens is an avascular structure but receives its nutrition mostly from aqueous humor.
  • Some nutrition derived from vitreous humor too.
  • Lens does not need much oxygen, but receives glucose as its main energy source.
  • Glucose from the aqueous (mainly) & vitreous diffuses into the lens.

Exam Important

  • Crystalline lens develops from Surface ectoderm.
  • Water content in lens is 64%.
  • Lens has a respiratory quotient of 1.
  • Crystalline lens absorbs light rays shorter than 350 nm.
  • Diameter of an adult crystalline lens is 9-10 mm.
  • Thickness of the adult crystalline lens is about 5 mm.
  • The capsule of the crystalline lens is thinnest at posterior pole.
  • Epithelium is absent in lens on Posterior surface.
  • Oldest lens fibres are found in Nucleus.
  • The youngest lens fibres are present in Superficial layer of the cortex.
  • The lens fibres meet around the Y-shaped sutures in Embryonic nucleus of the crystalline lens.
  • Infantile nucleus of the crystalline lens refers to the nucleus developed from Birth to puberty.
  • Hyaloideocapsular ligament of Weiger or retrolental ligament is a strong adhesion b/w the lens & posterior capsule.
  • Strongest & thickest attachment of zonule is at just anterior to the equator.
  • The crystalline lens derives its nourishment from Aqueous and vitreous humor.
  • Vitamin A does not handle free radicals inside lens.
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