Post Test 1 Flashcards
What point should always appear in front of the pupil?
(MRP) Major Reference Point
Characteristics of minus lens
minifies ( makes things smaller with motion), thick edges, thin center, diverges light
Characteristics of plus lens
magnifies (against motion), thin edges, thick center, converges light
What is the first step you always do when choosing a lens?
Surface and internal inspection of uncut lens
How is the power created in lenses
nominal power sum of the front and back curves
Describe the steps in lensometry
- find two principal powers of lens (like on power cross)
- determine which principal power is “warmer”
- Warmer number is your “A” reading or sphere
- Put “A” reading on the power wheel
- When you look into your lensometer:
if you see sphere lines then the reading on the axis wheel is your “B” reading or axis reading. If you see cylinder lines then turn your axis wheel 090 degrees and you will see your sphere lines. Now the reading on the axis wheel is your “B” reading. - Make left over principal power your “C” reading.
- Determine your Cylinder with the formula; Cyl = C-A
What’s the purpose of the eyepiece?
To eliminate the normal accommodation of the eye when focused for the user
What’s the formula for Cylinder?
Cylinder = C-A
Describe the steps to transposition
- Add the sphere and cylinder together to get the new sphere power
- Change the sign of the cylinder, but leave the value the same
- Add or subtract 090 to the axis as long as the new axis is between 1-180 degrees
What are the two methods to measure a PD?
Ruler/penlight and pupilometer
How do you avoid parallax error when measuring PD?
By being the same height and directly in front of the patient when measuring
What is A? (Boxing Method)
the horizontal eyesize
What is B? (Boxing Method)
vertical depth
What is GC? (Boxing Method)
the center point of an uncut lens, the boxing center
What is GCD? (Boxing Method)
geometric center distance, the separation between the GC of the right and left lenses (NOTE: GCD=A+DBL)
