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22 Cards in this Set
- Front
- Back
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What types of lenses are myopia and hyperopia treated with?
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SPEHERICAL lenses of MINUS and PLUS power
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What type of spherical lens do you use to correct a myope?
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MINUS spherical lens
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What type of lens do you use to correct a HYPEROPE?
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PLUS spherical lens
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What type of CURVES does a spherical lens have?
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CIRCULAR CURVES
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What is a MERIDIAN?
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Any RADIAL cross-section of a lens that includes the centre of the lens
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When looking straight at a spherical lens, as it sits before the eye, what is remarkable about any cross section of the lens?
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it will have the same lens CURVATURES and the same POWER.
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Is the rotational before the eye, of a spherical lens, important?
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NO! because the meridians all have the same power.
So as long as the centre of the lens is infront of the centre of the eye, whether there is rotation of the lens or not, is unimportant. |
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Does a spherical lens has the same power in every meridian?
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Yes it does
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How are SPHERICAL lenses SPECIFIED?
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By their spherical power only.
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What type of lens is ASTIGMATISM corrected with?
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SPHERO-CYLINDRICAL lens
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In a sphero-cylidrical lens, how do the meridians differ from a spherical lens?
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They have different powers in different meridians
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In a sphero-cylidrical lens, the power varies from meridian to meridian. What are the PRINCIPAL meridians?
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The meridian of GREATEST power
The meridian of LEAST power They are 90 degrees apart. |
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How are sphero-cylindrical lenses specified?
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By the POWERS in the PRINCIPAL meridians
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What are the two main meridians in a CYLINDRICAL lens?
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The AXIS MERIDIAN and the PLANO MERIDIAN
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What is the PLANO AXIS meridian?
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A cylindrical lens has a curve surface and a "flat" surface.
The flat or plane surface or meridian, has no power (doesn't bend light) |
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What is the POWER meridian?
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The curved surface, however, bends light. the meridian through this surface has the maximum power. it is 90 degrees to the plano meridian.
The ORIENTATION of these meridians, is ESSENTIAL. |
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Instead of creating a FOCAL POINT, as in a SPHERICAL lens, what does a CYLINDRICAL lens create?
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a focal LINE.
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What type of movement will a ROTATING cylinder lens produce?
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A scissor movement (not with or against, as with a spherical lens)
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What is a CONVEX cylinder referred to?
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a PLUS CYLINDER
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What is a CONCAVE cylinder lens referred to?
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a MINUS CYLINDER
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What does the CYLINDER axis refer to?
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The PLANO AXIS MERIDIAN.
The orientation of this axis must be specified. Remember, there is no power through this axis. |
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How is the CYLINDER or AXIS meridian, noted?
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Noted as being between 1 and 180 degrees.
Measured COUNTER-CLOCKWISE, like a protractor. |
