Keratometry Flashcards
which refractive errors does the keratometer measure in
the 2 prinicpal meridieans of the cornea
the keratometer provides information about the ______ not the ______
astigmatism
not about the spherical ametropia
what is another name for the keratometer
ophthalmometer
it meausre the curvature of the central ___ to ___mm of the ______ surface of the cornea
3.5-3.75
anterior
the keratometre is used to predict ______ after refraction
total astigmatism
keratometer is used for ______ fitting and _____
CL fitting
follow-up
the cornea acts as a ____ mirror and ______ refracting surface
convex
convex
what eye movements hinder the measurement
nystagmoid
what do you double the mires using
prism
wollaston or biprism is used in ______ keratometers
-the drum is rotated for measurement in the ____meridian
2 position keratometers
-second
B & L keratometer is used in _____ keratometers.
-uses 2 prisns oriented how?
one postion
verticaly &horiz
what do the upper and lower apertures use to keep the mires in sharp focus
scheiner’s disk principle
image is virtual and erect and smaller than the object
mires
what is the relationship between mm and diopters
reciprocal
what kind of radius does a steep cornea have
what kind of radius does a flat cornea have
short
long
the average cornea is
43 to 44 D
how much does the cornea flatten btwn birth and age 1
5-10 D
what is the range of B&L keratometer
36-52D
what can the range of the keratometer be extended using
spherical lenses
more power in the vertical meridian is
with the rule
more power in the horizontal meridian is
against the rule
what is not w/in 30 degrees of 90 or 180
oblique
ex. 42.00/43.00 @055 1.00 oblique
the two principal meridians are NOT 90 degrees apart
irregular
ex. 45.00@165/52.00@90 7.00irregualr
empirically predicts total refractive astig from K readings
javal’s rule
