Anatomy Of Cornea

ANATOMY OF CORNEA

Q. 1

For transplantation. cornea is preserved in:

 A

Modified MK medium

 B

Glycerine medium

 C

Wet medium

 D

All of the above

Q. 1

For transplantation. cornea is preserved in:

 A

Modified MK medium

 B

Glycerine medium

 C

Wet medium

 D

All of the above

Ans. A

Explanation:

Ans. Modified MK medium


Q. 2

True about anatomy of adult cornea:

 A

Horizontal diameter is 12 mm

 B

Horizontal diameter is 10 mm

 C

In megalocornea diameter is >12 mm

 D

Vertical diameter> Horizontal diameter

Q. 2

True about anatomy of adult cornea:

 A

Horizontal diameter is 12 mm

 B

Horizontal diameter is 10 mm

 C

In megalocornea diameter is >12 mm

 D

Vertical diameter> Horizontal diameter

Ans. A

Explanation:

Ans. Horizontal diameter is 12 mm


Q. 3

True about cornea:

 A

Power is 43 D

 B

Majority of refraction occur at air-tear interface

 C

With the rule astigmatism is present because vertical meridian more sleep than horizontal meridian

 D

All

Q. 3

True about cornea:

 A

Power is 43 D

 B

Majority of refraction occur at air-tear interface

 C

With the rule astigmatism is present because vertical meridian more sleep than horizontal meridian

 D

All

Ans. D

Explanation:

Ans. All A, B and C


Q. 4

Orange-skin cornea results due to:

 A

Chalcosis

 B

Siderosis

 C

Ammonia burn

 D

Mustard gas

Q. 4

Orange-skin cornea results due to:

 A

Chalcosis

 B

Siderosis

 C

Ammonia burn

 D

Mustard gas

Ans. D

Explanation:

Ans. Mustard gas


Q. 5

Refractive index of cornea is:

September 2007

 A

1.28

 B

1.38

 C

1.48

 D

1.58

Q. 5

Refractive index of cornea is:

September 2007

 A

1.28

 B

1.38

 C

1.48

 D

1.58

Ans. B

Explanation:

Ans. B: 1.38

Looked at from the front the cornea is about 12 mm horizontally and 11 mm vertically.

It is the first and most important refracting surface of the eye, having a power of about 43 D.

The anterior surface has a radius of curvature of about 7.8 m, the posterior surface 6.5 mm, and the central thickness is about 0.5 mm.

Cornea is comprised of several layers and, therefore, the optical properties are measured for the whole cornea rather than generalizing from a tissue sample.


Q. 6

Cornea gets its nourishment mainly from:

September 2009

 A

Atmosphere

 B

Aqueous humour

 C

Vitreous humour

 D

Corneal vessels

Q. 6

Cornea gets its nourishment mainly from:

September 2009

 A

Atmosphere

 B

Aqueous humour

 C

Vitreous humour

 D

Corneal vessels

Ans. B

Explanation:

Ans. B: Aqueous humour

Cornea consists of five layers, starting from the outside: (1) the stratified squamous epithelium; (2) Bowman’s layer; (3) the stroma (substantia propria); (4) Descemet’s membrane; and (5) the endothelium.

The cornea is avascular, receiving its nourishment by permeation through spaces between the lamellae. The sources of nourishment are the aqueous humour (90%), the tears and the limbal capillaries.

The cornea is innervated by the long ciliary and other nerves of the surrounding conjunctiva, which are all branches of the ophthalmic division of the trigeminal nerve. Innervation is entirely sensory.


Q. 7

The critical angel of cornea-air interface is

 A

36°

 B

46°

 C

56°

 D

66°

Q. 7

The critical angel of cornea-air interface is

 A

36°

 B

46°

 C

56°

 D

66°

Ans. B

Explanation:

Ans. b. 46°


Q. 8

Copper deposition in cornea leads to‑

 A

Keratoconus

 B

Keratoglobus

 C

KF ring

 D

Siderosis

Q. 8

Copper deposition in cornea leads to‑

 A

Keratoconus

 B

Keratoglobus

 C

KF ring

 D

Siderosis

Ans. C

Explanation:

Ans. is ‘c’ i.e., KF ring

Retention of Foreign bodies

  • The retention of a foreign body adds considerably to the danger of a penetrating injury.
  • The foreign bodies most likely to penetrate and be retained in the eye are minute chips of iron or steel (accounting for 90% of the foreign bodies in industry), stone, and particles of glass, lead pellets, copper percussion caps and less frequently, spicules of wood.
  • In chipping stone with an iron chisel, it is commonly a chip of the chisel and not of the stone which enters the eye.
  • Chalcosis is perforating injury to eye with metal containing copper (Cu). Copper deposition can lead to :‑
  1. Grayish-green/golden brown discoloration of peripheral cornea called Kayser-Fleisher ring.
  2. Sunflower (Petal of flower) cataract due to deposition of copper under the posterior capsule of the lens.
  3. Golden plaque at posterior pole of the retina.
  • Siderosis is caused by an iron foreign body. Iron deposition can cause :‑
  1. Characteristic and earliest manifestation is rusty deposits of iron in a ring shaped manner on anterior surface of capsule of the lens. Later cataract develops.
  2. Initially iris is stained greenish and later become reddish-brown —> Heterochromia iridis.
  3. Pigmentary degeneration of retina.
  4. Secondary open angle glaucoma.

Q. 9

Conjunctival mucosal overgrowth over cornea‑

 A

Pterygium

 B

Pingecula

 C

Vernal keratoconjunctivitis

 D

Herbert’s pit

Q. 9

Conjunctival mucosal overgrowth over cornea‑

 A

Pterygium

 B

Pingecula

 C

Vernal keratoconjunctivitis

 D

Herbert’s pit

Ans. A

Explanation:

Ans. is ‘a’ i.e., Pterygium 

Pterygium

  • Pterygium is a non-cancerous (non-neoplastic) growth of conjunctiva, characterized by a wing-shaped fold of conjunctiva encroaching upon the cornea from either side within the interpalpebral fissure. Pterygium is always situated in the palpebral aperture.
  • Pathologically Pterygium is a degenerative and hyperplastic condition of conjunctiva. The subconjunctival tissue undergoes elastotic degeneration and proliferates as vascularized granulation tissue under the epithelium, which ultimately encroaches the cornea. The corneal epithelium, Bowman’s layer and stroma are destroyed.

Etiology & Clinical features

  • Pterygium is more common in people with excess outdoor exposure to sunlight (UV rays), dry heat, high wind and abundance of dust. Therefore it is more common in those who work outdoors.
  • Clinically it presents as a triangular fold of conjunctiva encroaching the cornea in the area of palpebral aperture, usually on the nasal side. Other findings are stocker’s line (deposition of iron)
  • Ptergyium is an asymptomatic condition in the early stages, except for cosmetic intolerance. Visual disturbance or corneal astigmatism may occur. Visual disturbances are due to encroachment of pterygium on pupillary area or corneal astigmatism. Occasionally diplopia may occur due to limitation of ocular movements.

Treatment

  •  Asymptomatic pterygium which is not progressive is best left alone. Surgical excision is the only satisfactory treatment and is indicated for : – 1) Cosmetic reasons, 2) Continued progression threatening to encroach onto the pupillary area (once the pterygium has encroached pupillary area, wait till it crosses on the other side), 3) Diplopia due to interference in ocular movement.

Q. 10

Superficial corneal vascularization is caused by‑

 A

Contact lens

 B

Graft rejection

 C

Chemical burn

 D

Interstitial keratitis

Q. 10

Superficial corneal vascularization is caused by‑

 A

Contact lens

 B

Graft rejection

 C

Chemical burn

 D

Interstitial keratitis

Ans. A

Explanation:

Ans. is ‘a’ i.e., Contact lens & ‘to’ i.e., Graft rejection 

Superficial                                                        Deep

Superficial corneal ulcer

Contact lens user

Trachoma

Rosacea keratitis

Phlyctenular keratoconjunctivitis o Cornea graft rejection

 Interstitial keratitis

 Disciforrn keratitis 

Deep corneal ulcer

Chemical burns

 Sclerosing keratitis

  • Viral infection can cause superficial corneal ulcer as well as disciform keratitis.

Q. 11

Stem cells are present where in cornea?

 A

Limbus

 B

Stroma

 C

Epithelium

 D

Descmet’s membrane

Q. 11

Stem cells are present where in cornea?

 A

Limbus

 B

Stroma

 C

Epithelium

 D

Descmet’s membrane

Ans. A

Explanation:

Limbal stem cells (also c/d corneal epithelial stem cells) are stem cells located in the basal epithelial layer of the corneal limbus.



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