REFRACTED ERRORS Flashcards
AXIAL LENGTH
The eye is a compound lens system that refracts light. It is the power of this lens system and the axial length of the eye that determine the refractive error of the eye.
A 1 mm change in axial length results in how many diopters difference in the power of the eye?
I dont know
Emmetropia
The emmetropic eye is a normal eye in which all the rays of light from a distant object are focused sharply on the retina. NO refractive error is present. There is no need for corrective distance lenses. PLANO Sph
Ametropia
The plus power of the eye can be excessive or inadequate, possibly resulting in decreased vision. In both instances, the power can be corrected. This is done so by changing the total plus power of the eye with lenses so that it IS at an adequate level.
Myopia
Also called near-sightedness, this is a condition where parallel light rays come to a focus at a point just in front of the retina
Hyperopia
I dont know
Minus lenses and all the characteristics
Also, when an image is viewed through a minus lens, the image will appear to move in the same direction as the lens when it is moved side to side or up and down. This is referred to as “with motion”. Minus lenses diverge rays of light. Light going through the thinnest part of the lens (the optical center) is NOT refracted. This is because it is perpendicular to the lens surface. Everywhere else, the angle of incidence is not 90 degrees and will therefore be refracted according to Snell’s law.
Plus lenses and all their characteristics
AGAINST MOTION
An image viewed through a plus lens appears magnified. OTC reading glasses are plus lenses, thus people call them “magnifiers”. When an image is viewed through a plus lens, the image will appear to move against the motion of the lens as it is moved side to side or up and down. This is referred to as “against motion”. Plus lenses converge rays of light. Light rays going through the thickest part of the lens (the optical center) are NOT refracted.
Which way is light bent through a prism?
Light is always bent towards the base of a prism. If a convex lens is 2 prisms placed base to base, the light will converge inward towards the base of each prism.
The speed at which waves travel is called
Velocity
The Color in the visible spectrum with the shortest wavelength is
Violet
The separation of white light into the spectral component is
Dispersion
In reflection the angle of incidence is equal to
The angle of reflection
What does the Index of refraction tell you?
It tells us the amount by which light slows in a given medium
The power of a lens is measured in
Diopters
Which part of the eye has the greatest refractive power
Cornea
Distance from the center of a lens to the focal point is called
Focal Length
When going from a higher IR to a lower IR light will be reflected towards the normal?
False
If the focal length is 16 inches what is the power of the lens
2.50 D
What is the focal length in cm if the power of a lens in 5.00 D
100/5= 20 cm
A larger radius of a curvature has a steeper curve
False
The higher the power of a lens is the longer the focal length will be
False- SHORTER
Light intensity is measured by
foot candles
The bending of light rays is known as
Refraction
The power of a lens is determined by its
Refracted index and Curvature
A convex lens will
Magnify ++
A myopic eye is too long and required a
Minus lense
The overall power of the eye is
PLUS +++
Convergence is achieved with a
PLUS Lens
Formula for velocity of light is
wavelength X frequency
Index of refraction is an expression of
Optical density
What kind of lens has a virtual focal point?
CONCAVE
What causes light to bend when entering a new medium
Change in speed
When a plus lens is moved the image will move
against motion
When a minus lense is moved the image will
it will move along
The speed of light increases or decreases depending on
Index of refraction
The refracted index of air is
1.00
Snell law is the
Law of refraction
In reflection the angle incidence is equal to the
Angle of reflection
The hyperopeic eye has ( ) plus power
too little
The ray that is entering a medium is the
Incident ray
A minus lense is Apex to Apex?
true
A concave will diververge light rays
A convex will diverge light rays?
true
False
