Test 7 (Optical prescriptions, spectacle lenses)
1. The following transpositions are correct:
a. PL / -2.00 X 180 = -2.00 / +2.00 X 90

b. +2.00 / -0.50 X 60 = +2.50 / +0.50 X 150 

c. -1.25 / +0.75 X 4 = -0.50 / -0.75 X 86 

d. +7.00 / -2.00 X 78 = +5.00 / +2.00 X 168

e. -0.25 /-3.00 X 50 = -3.25 / +3.00 X 140


2. When transposing +3.00/-1.00X 90 to the base curve -5.00, 
    the correct answer should be:
a. +8.00 DS/-5.00DC axis 180/-6.00DC axis 90

b. +8.00 DS/-5.00DC axis 180/-6.00DC axis 180

c. +8.00 DS/ -5.00DC axis 90/-6.00DC axis 180

d. -2.00DS/ -5.00DC axis 90/-6.00 DC axis 90

e. -2.00DS/ -5.00DC axis 180/-6.00DC axis 90

3.  The following are true about the identity of an unknown lens when 
     viewed through a cross made up of two lines crossed at 900:
a. there is no distortion of the cross if the lens is spherical

b. an astigmatic lens always causes distortion of the cross

c. 'scissors' movement of the cross when the lens is 
    rotated suggests the lens is astigmatic

d. if the cross moved in opposite direction to the lens, 
     the lens is likely to be concave

e. displacement of the line on  cross suggests the presence
    of prism within the lens.


4. Regarding the Geneva lens measure:

a. it can only be used to measure crown glass

b. it measures the base curve of a lens

c. it makes use of the principle that the total power of 
    a thin lens is equal to the sum of its surface power

d. it can be used to measure the thickness of a lens 

e. it can be used to measure the diameter of a lens


5. The focimeter:
a. contains a convex collimating lens 

b. contains a collimating lens that converge the incoming 

b. uses green light to eliminate spherical aberration

c. contains a telescope system for viewing

d. gives a ring of dots if the lens has no cylindrical power


6. The focimeter can measure:
a. back vertex power of the lens

b. prism

c. axis of the cylinder

d. optic centre of the lens

e. refractive index of the lens


7. Regarding tinted lenses:
a. the lenses always change colour with light

b. they work by either absorbing the light or reflecting 
    the light

c. transmittance curve of a tinted lens measures the 
    percentage of light transmission for each wavelength

d. the protective goggles used in laser room are made up 
    of tinted lenses.

e. lenses with solid tint have uniform light absorption 


8. True statements about anti-reflective coatings include:
a. the principle of destructive interference applies to
    anti-reflective coatings

b. the thickness of the coating is a quarter of the 
    wavelength of the incident light

c. they cause the lenses to grow dark in bright light

d. they absorb ultraviolet light

e. they can only be used on plastic lenses


9. Photochromic lenses:
a. usually have a more rapid darkening process than 
    lightening process
b. give different tints according to the wavelengths

c. tend to become darkened with repeated use

d. that made of glass usually employed organic 
    photochromic compounds

e. tend to darken more rapidly if the environmental 
    temperature is low

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