Test 25

1. The following changes may be noted during pregnancy:

a. increased corneal curvature

b. hypermetropic shift due to gestational diabetes

c. anterior displacement of the lens

d. contact lens intolerance

e. increased corneal thickness
 

Answer
a. T   b.F   c.F   d.T   e.F
Increased corneal curvature is seen in late pregnancy.
Myopic shift is a sign of gestational diabetes.
 

2. Enhanced illumination is beneficial in the following patients:

a. posterior subcapsular cataract

b. nuclear sclerosis

c. retinitis pigmentosa

d. albinism

e. age-related macular degeneration
 

Answer
a.F   b.T   c.F   d.F   e.T
Glare is a problem in posterior subcapsular cataract with increased illumination. Posterior subcapsular cataract is also common in retinitis pigmentosa. 
Increased illumination causes macular photostress in albinism.

3. The following are true about lenses made from polycarbonate:

a. for the same dioptre power lenses made from 
    polycarbonate is thinner than the normal plastic lenses

b. polycarbonate lenses cause less chromatic aberration
    than normal plastic lenses

c. polycarbonate lenses are softer than normal plastic 
    lenses

d. polycarbonate lenses have a lower refractive index 
    than normal plastic lenses

e. they are safe as protective glasses

 
Answer
a.T   b.F   c.T   d.F   e.T
Polycarbonate is softer, causes more chromatic aberration and has a higher refractive index than normal plastic lenses

4. With regard to chromatic aberration:

a. lens with high Abbe value has more chromatic 
    aberration

b. lenses with high refractive index has low chromatic
    aberration

c. plano-convex lens has less chromatic aberration 
    than biconvex lenses

d. chromatic aberration can be reduced by making the
    periphery steeper than the centre

e. doublet can be used to reduce chromatic aberration
 

Answer
a.F    b.F   c.T   d.F   e.T
Abbe value is used to identify the amount of chromatic aberration in a lens. Higher value is associated with less chromatic aberration and vice versa. 
Chromatic aberration is independent of refractive index.
Chromatic aberration can be reduced by making the periphery flatter than the centre.

5. In compound microscope:

a. two convex lenses are used 

b. the distance between the two lenses is the combined 
    focal lengths of the lenses

c. the image formed is real and magnified

d. the image is horizontally and vertically inverted

e. the incorporation of zoom lens system allows 
    magnification without altering the position of image 
    and object

Answer
a.T   b.F  c.T   d.T   e.T
The distance between the two lenses are longer than the combined distance of the focal lengths of the two lenses.

 

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