Refractive System Of Eye

REFRACTIVE SYSTEM OF EYE

Q. 1 Highest refractive index in eye is of:
 A Anterior surface of lens
 B Post surface of lens
 C Cornea
 D Centre of lens
Q. 1 Highest refractive index in eye is of:
 A Anterior surface of lens
 B Post surface of lens
 C Cornea
 D Centre of lens
Ans. D

Explanation:

Centre of lens


Q. 2

What is the refractive power of cornea?

 A

15

 B

30

 C

43

 D

60

Q. 2

What is the refractive power of cornea?

 A

15

 B

30

 C

43

 D

60

Ans. C

Explanation:

The refractive power of the cornea is 43D. The maximum refractive power of an emmetropic eye is 63D, with an axial length of the globe measuring 23.5mm. The lens accounts for 10-20 diopters depending upon accommodation. However, refractive power of the eye is not simply the sum of these two values. 
 
Refractive power of a newborn cornea is 51D
Refractive power of a fetal cornea is 52 – 53 D
 
Ref: Ophthalmology: a short textbook By Gerhard K. Lang page 425.


Q. 3

Refractive power of eye can be changed by:

 A

Radial keratotomy

 B

Keratomileusis

 C

IOL

 D

All

Q. 3

Refractive power of eye can be changed by:

 A

Radial keratotomy

 B

Keratomileusis

 C

IOL

 D

All

Ans. D

Explanation:

A i.e. Radial keratotomy; B i.e Keratomileusis; C i.e. IOL

Quiz In Between


Q. 4

The refractive power of an emmetropic eye is about:

 A

+50D

 B

+55D

 C

+60D

 D

+65D

Q. 4

The refractive power of an emmetropic eye is about:

 A

+50D

 B

+55D

 C

+60D

 D

+65D

Ans. C

Explanation:

Ans. +60D


Q. 5

In the media of the eye, highest refractive index is of the:

 A

Cornea

 B

Aqueous humour

 C

Lens

 D

Vitreous humour

Q. 5

In the media of the eye, highest refractive index is of the:

 A

Cornea

 B

Aqueous humour

 C

Lens

 D

Vitreous humour

Ans. C

Explanation:

Ans. Lens


Q. 6

The term anisometropia indicates

 A

Refractive error

 B

Long vision

 C

Short vision

 D

Ageing process

Q. 6

The term anisometropia indicates

 A

Refractive error

 B

Long vision

 C

Short vision

 D

Ageing process

Ans. A

Explanation:

Ans. Refractive error

Quiz In Between


Q. 7

1mm change in the axial length of the eyeball produces a change in refractive index by:             

March 2005

 A

1 D

 B

2 D

 C

3 D

 D

4 D

Q. 7

1mm change in the axial length of the eyeball produces a change in refractive index by:             

March 2005

 A

1 D

 B

2 D

 C

3 D

 D

4 D

Ans. C

Explanation:

Ans. C: 3D

1mm change in the axial length of the eyeball produces a change in refractive index by 3 D. Elongation produces myopia and shortening causes hypermetropia.

1 mm change in the radius of curvature of the cornea produces a 6 D refractive change.

Steeper (more curved) corneas produce myopia and flatter corneas hypermetropia.


Q. 8

Eye structure with maximum refractive power:

March 2007

 A

Anterior surface of lens

 B

Posterior surface of lens

 C

Anterior surface of cornea

 D

Posterior surface of cornea

Q. 8

Eye structure with maximum refractive power:

March 2007

 A

Anterior surface of lens

 B

Posterior surface of lens

 C

Anterior surface of cornea

 D

Posterior surface of cornea

Ans. C

Explanation:

Ans. C: Anterior surface of cornea

Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye’s total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres.

While the cornea contributes most of the eye’s focusing power, its focus is fixed.

The curvature of the lens, on the other hand, can be adjusted to “tune” the focus depending upon the object’s distance.


Q. 9

Power of normal eye is:         

September 2007

 A

+6 D

 B

+10 D

 C

+16D

 D

+60 D

Q. 9

Power of normal eye is:         

September 2007

 A

+6 D

 B

+10 D

 C

+16D

 D

+60 D

Ans. D

Explanation:

Ans. D: +60 D

The power of the front surface of the cornea is about 43D, and, if it were in air, the power of the crystalline lens at rest (its minimum power, not accommodating) would be about 20D.

This adds up to 63D.

But the ‘schematic’ eye is said to have 60 D of power: a little power is lost when the ray exits the cornea into aqueous, since this means it is going from a material with higher index to a material of lower index.

Quiz In Between


Q. 10

Refractive index of cornea is:

September 2007

 A

1.28

 B

1.38

 C

1.48

 D

1.58

Q. 10

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. 11

Maximum refractive index ‑

 A

Cornea

 B

Air

 C

Lens

 D

Vitreous

Q. 11

Maximum refractive index ‑

 A

Cornea

 B

Air

 C

Lens

 D

Vitreous

Ans. C

Explanation:

Ans. is ‘c’ i.e., Lens

Lens has maximum refractive index among the refractive structures of eye. The refractive indices of the successive layers of lens increase from the periphery towards the nucleus.


Q. 12

Refractive index of vitreous humor ‑

 A

1

 B

1-30

 C

14

 D

1.336

Q. 12

Refractive index of vitreous humor ‑

 A

1

 B

1-30

 C

14

 D

1.336

Ans. D

Explanation:

Ans. is ‘d’ i.e., 1.336


Q. 13

Refractive index of this structure marked with arrow  is about:

 A

1.000

 B

1.330

 C

1.400

 D

1.370

Q. 13

Refractive index of this structure marked with arrow  is about:

 A

1.000

 B

1.330

 C

1.400

 D

1.370

Ans. C

Explanation:

Ans:C.)1.400.

This structure is crystalline lens

Light rays reflecting from distant objects are focused on the retina after they passed through the cornea, aqueous humor, the lens, and finally the vitreous humor.

The refractive index of human lens varies from approximately 1.406 in the central layers down to 1.386 in less dense layers of the lens

 List of Refractive Indices of Various Components of the Human Eye
Medium Refractive Index
Air 1.000
Cornea 1.376
Aqueous Humor 1.336
Lens 1.406
Vitreous Humor 1.336

Quiz In Between



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