Optics and Spectacles 3% Flashcards
What are the steps to transposing a prescription?
Algebraically add the sphere and cylinder in the example. Change the sign of the cyl from + to - or vice versa. Add (or subtract) 90 degrees from axis.
Transpose :
-4.00+2.00x90
-2.00-2.00x180
Transposed
+5.00-2.50x75
-2.50+2.50x165
A_____is a way to express a complex prescription which has cyl in a more simple spherical format
Spherical equivalent
How do you calculate spherical equivalent?
take 1/2 the cyl add to sphere then drop the cyl and axis
Lenses should be centered so that the pt looks through the _____
optical center of the lens
The thinnest part of minus lens or the thickest part of the plus lens
optical center
If you don’t center the lens _____effects will be induced
prismatic
________glasses are intentionally decentered to allow for convergence and down gaze when they read
Reading
How do you measure pupillary distance?
from nasal edge of one pupil to the the temporal edge of the other in mm or if pt has only one eye from center of bridge of nose to center of good eye pupil
How do you measure PD for pt with strabismus?
Measure from inner canthus of one eye to outer canthus of opposite eye OR occlude deviating eye and measure from center of the bridge of the nose to the center of the uncovered eye, then repeat with the other eye covered. The sum of these 2 measurements is PD.
This instrument is used to measure vertex distance in mm
distometer
How do you measure vertex distance?
from back surface of lens to the front surface of the K(with the distometer pt eye is closed, it allows 1mm for eyelid thickness)
What is the average vertex distance?
12mm
If you have a _____power Rx it doesn’t matter how far away the prescription is from their eye but if they have a _____ powered prescription then it’s very important
small
high
