Chapter 8  (Aberration of optical system)
1. The following are true about chromatic aberration:
a. it results from the fact that longer wavelength is deviated 
    more than shorter wavelength.

b. it does not occur with light of same wavelength

c. it results from the dispersive power of a material

d. it is dependent on the refractive index of a material

e. it can be reduced by combining crown and flint glass

2. Duochrome test::
a. uses letters or numbers of different colours against the same background

b. uses blue and red colours

c. is sensitive to changes in refraction of 0.25D or less

d. is useful in myopic patients to avoid undercorrection

e. can not be used in colour blind patients


3. Spherical aberration in human eye is reduced by the following:
a. the anterior surface of the cornea is flatter peripherally than centrally

b. the cortex of the lens has a higher refractive index than the nucleus

c. the lens has variable anterior surface curvature

d. the retina has a radius of curvature which is shorter centrally than 

e. the vitreous reduces spherical aberration


4. The following are true about spherical aberration:
a. it is responsible for reduced vision in dilated pupil

b. it results from the prismatic effect of the peripheral parts of a spherical lens

c. light passing through the periphery of a spherical lens is deviated more 
    than those through the paraxial zone of the lens

d. it can be reduced by using a lens with less dispersive power

e. it can be reduced with a doublet.


5. Oblique astigmatism
a. occurs when light passing through the lens obliquely

b. is more troublesome the higher the power of the lens

c. is most troublesome in the reading section of the varifocal glasses 

d. is worse with meniscus lenses than biconvex or biconcave lens

e. of spectacle can be reduced with pantoscopic tilt


6. Best form lenses is used to reduce:
a. chromatic aberration

b. oblique astigmatism

c. spherical aberration

d. coma

e. glare


7. Oblique astigmatism in the eye is reduced by::
a. aplanatic curvature of the cornea 

b. the vitreous

c. the variable refractive indexi of the lens

d. the spherical surface of the retina

e. the peripheral retina has less resolving power than the central cornea



8. The following are true about image distortion through strong lenses:
a. it is mainly the result of chromatic aberration

b. it is mainly the result of spherical aberration

c. pin-cushion distortion occurs with high minus lens

d. barrel distortion occurs with high plus lens

e. it can be reduced by getting the patient to use contact lenses


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