Lensometry Flashcards
lensometer used to measure what?
vertex power of a lens
sphere powers (within +/- 6.50 D) should not differ anymore than what? cylinder powers that are (less than or equal to 2.00 D) should not differ anymore than? cyl axes (within .25 D) should not differ anymore than?
+/- 0.13D
+/- 0.13D
+/- 14 deg (smaller axes can differ by more than larger ones because patient wont notice)
back vertex power is measured from where? front vertex power?
back surface
front surface
PD is what? spectacle PD?
PD is what patient has
spectacle PD is what the glasses have (we usually want PD to equal spectacle PD unless we want to induce prism).
ADDS are always what power? they are added to what?
positive
only the sphere power in distance prescription (NOT CYL)
Telescope portion of lensometer is made up of?
eyepiece, reticle and objective lens
badal system is made up of?
badal lens, target (mires) and light
black numbers move drum in which direction and signify? red numbers?
toward you, positive numbers
away from you, negative numbers
With zero setting and NO glasses, targets image (mires) are seen at what distance?
infinity, gives a sharp image
when a positive unknown lens is introduced, light converges and mires are out of focus. To re focus and get a clear image, the target is moved in what direction?
closer to generate more diverging rays
when a negative unknown lens is introduced, light is diverged. the target needs to be moved where to get a clear image?
away in order to generate converging rays
every 2.5mm of movement is equal to how much power?
1.00D
if the position of the mire is toward the nosepiece what base would it be? if away from nosepiece? toward bottom of lens? toward top of lens?
base in
base out
base down
base up
what is important to remember about bifocals in the lensometer?
TURN THEM AROUND
what is carrier? near? intermediate?
carrier=distance (sphere in distance prescription)
near= sphere in distance + ADD prescription
intermediate= sphere in distance +1/2ADD prescription
