Handout 4 Flashcards
the normal, imaginary line connecting the centers of curvature of the two surfaces of the lens
optic axis
the point on the optic axis intersected by the path of a ray of light between the 2 surfaces that, after refraction by the second surface, is parallel to its path before the incidence at the first surface (no prismatic effect)
optic center
spherical, homocentric, sitgmatic lenses refract light how?
light rays meet at one common point, convex and concave
cylindrical, astigatism kens refract light how?
light rays to focal LINE
toric, spherocyl, astig., nonhomocentric refract light how?
light rays to form two line images perpendicular from each other
the change in vergence that occurs when light passes through a lens
refractive power
approximate power aka is measure with
nominal power,lens clock
lens power specified in terms of front and back surface powers with out regards to thickness
approximate power,nominal power
series of lenses separated by air, having different index of refractions are called
equivalent systems /equivalent power
both are specified in terms of refracting power for emergent rays of light at the back or front surface of the system
front vertex power and back vertex power
front vertex power aka
neutralizing
typically measure using hand neutralization, and using a focimeter by placing front surface of lens
front vertex/neutralizing power
the ability of the lens to focus parallel rays of light at a given plane
effective power
the greter the effect on vergence
the more effective the lens is
the lens power needed to correct a pts ametropia is dependent on
the distance from wearers eyes
effective power aka
back vertex power
is used to indicate the change in lens power required if a lens is moved from one position to another
effective power
Feff : as lenses are moved further from the eye
plus power increases
Feff: as lenes are moved closer to the eye
minus power increases
> -4.00 D will require contact lens
lesser power
> +4.00 D will require contacts
higher power
if a presbyope is oving their glasses low they may need
a more effective plus lens
lens clock measures
powers of front and back surface power according to sag
the focimeter measures
vertex power of a lens
focusing system of the focimeter includes
light source + movable target + standard lems + lens stop
observation system
low powered keplerian telescope w/ an objective lens a secondary focal plae of the obj lens and an adjustable eyepiece
