Test 32

1. Wollaston prism is used in:

a. Javal-Schiotz's keratometer

b. pachymeter

c. operating microscope

d. slit-lamp

e. binocular
 

Answer

a.T   b.F   c.F   d.F  e.F
Wollaston prism is used to split a beam of unpolarised 
into two diverging which are oppositely polarized.

2. The following prisms can be used to form an erect image:

a. Dove prism

b. Nicol prism

c. Porro prism

d. Risley prism

e. Fresnel prism
 

Answer
a. T   b.F   c.T   d.F   e.F
Dove and Porro prisms are also called erectors.

 

3. Chavasse lens is useful in:

a. diplopia

b. aphakia

c. anisometropia

d. presbyopia

e. high myopia

 
Answer
a.T   b.F   c.F   d.F   e.F
Chavasse lens is a lens with irregular surface and
is used to depress the visual acuity while allowing
the eye to be see clearly from the front. It can be
used to treat patients with diplopia.

4. Wavefront analysis: 

a. is measured with an aberometer

b. should be performed on all patients undergoing LASIK

c. measures the overall refractive error of the eye

d. measures refractive error to about 0.01D

e. can be used to detect aberration outside the cornea
 

Answer
a.T   b.F   c.T   d.T   e.T
Wavefront analysis is performed by an instrument called
an aberometer. The aberometer can detect optical
errors at a fine level. Wavefront technology assesses
every ray of light that enters the eye and then determines what changes will produce the clearest image. Therefore, wavefront analysers precisely measure the overall refractive error of the entire eye, including any aberrations caused by the tear film, anterior and posterior cornea, lens, vitreous and retina. Remember that corneal topography systems can define corneal irregularities, but they cannot detect aberrations in other parts of the eye.
The wavefront sensor measures the refraction to submicron levels, or about 0.01 D. When a refraction is measured with today's conventional subjective tests, the accuracy is only to within 0.25 to 0.50 D. 

5. Safety glasses:

a. crumble rather than shatter on impact

b. can be made from laminated lenses

c. can be made by heating the glass just below its
    softening point and rapidly cooled.

d. are used in sports

e. decrease the visual acuity 

Answer
a.T   b.T   c.T   d.T   e.F
Safety glasses are used in industrial or sports in which ocular injury is likely.

 

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