Refractive Errors, Focal Length, Prisms, etc
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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| What is a prism? | A non-parallel sided medium.
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| Prisms bend light towards the...? | Base
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| Prisms deviate images towards the...? | Apex
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| What are prism diopters? | Units used to measure the power of a prism.
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| What is nearsighted vision, when the eyes are too strong, referred to as? | Myopia
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| What is myopia corrected with? | Minus lenses
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| What is farsighted vision, when the eyes are too weak, referred to as? | Hyperopia
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| What is used to correct hyperopia? | Plus lenses
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| What is astigmatism? | Eye has different powers in each meridian.
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| What is a meridian? | Line through the center of a circle.
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| Do steeper, shorter curves create weaker or stronger power? | Stronger (Remember SSS - steeper, shorter, stronger)
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| What is a toric surface? | A surface that is not spherical?
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| What lenses are used to correct astigmatism? | Cylinder or compound lenses
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| What has a toric surface on the front? | Plus cylinder lens
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| What has a toric surface on the back? | Minus cylinder lens
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| What has a toric surface on front and back | Bitoric lens
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| What is presbyopia? | Loss of accommodation as you age.
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| What lenses are used to correct presbyopia? | Plus lenses
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| What is the steepest curve on a toric surface? | Toric Cross Curve
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| What is the flattest curve on a toric surface? | Toric Base Curve
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| What are the Toric Cross Curve and Toric Base Curve referred to as? | Major Meridians
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| The major meridians are how many degrees apart? | 90 degrees
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| The major meridians create what is known as the...? | Toric cross
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| Convex surfaces have what kind of curves? | Plus curves
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| Concave surfaces have what kind of curve? | Minus curves
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| What is optical infinity? | 20 ft
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| What is the optical center? | The point of no prism because the front and back surfaces are parallel where vision is the sharpest.
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| Where is the optical center on a plus lens? | The thickest part
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| Where is the optical center on a minus lens? | The thinnest part
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| What is the optical axis? | The imaginary lines through the optical center of a lens perpendicular to the front and back surfaces.
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| The further the object point is from the lens, the ______ the image point is to the lens? | Closer
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| Rays of light coming from 20ft or beyond can be considered....? | Parallel
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| What is the focal point? | Image point when the object is at infinity.
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| What is the focal length of the lens? | Image distance from the lens to the image point when the object is at infinity.
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| Images formed by minus lenses are....? | Imaginary
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| What is conjugate foci? | A specified object point taken together with it's specific image point, that share the property of reversibility.
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| Older biconvex and biconcave lenses are known as...? | Flats
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| Lenses common today where only one side is concave or convex are known as....? | Bents
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| What is another word for "bents"? | Meniscus
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| What is the mechanical center? | The actual physical center of the lens, which can be different that the optical center.
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| Concave mirrors magnify images how? | Make them bigger
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| Convex mirrors magnify images how? | Make them smaller
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| When dealing with mirrors the angle of reflection will always equal what? | The angle of incidence
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| What is the image point? | The point to which the lens focuses light.
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| What is the distance between the two major meridians? | Interval of sturum
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| Formula for diopters in meters | D=1/f
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| Formula for diopters in inches | D=40/f
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| Prism formula | Prism=deviation(cm)/distance(m)
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