Log 4 - Determining power of lenses Flashcards
\_\_\_\_\_\_\_\_\_\_\_\_\_ is an instrument that determines A. Dioptric power of lens B. Axis of cylinder of a lens C. Amount of prism within a lens D. Position of optical center
Lensmeter
What two things can be seen while looking through the eyepiece of a traditional lensmeter
- Reticle
2. Target
__________ consists of two lines at right angles to each other and a set of increasingly larger circles that are centered around the point where the two lines intersect
- used to measure the amount of prism within a lens
Reticle
___________ is used to determine lens power, the axis of cylinder and the presence of prism. Most used is the cross type.
Target
_______ lines in lensmeter show the power of cylinder. _______ lines show the power of sphere
Vertical - cylinder
Horizontal - Sphere
Determine the lens prescription of the following readings:
reading A = +2.00 D
reading B = 135’
reading C = +3.00 D
reading A = Sphere
difference between reading C and A is the power of the cylinder +3.00 - (+2.00) = +1.00 D
reading B = the axis
Prescription = +2.00 +1.00 x 135
A ________ measures the sagittal depth of a lens
Lens Clock
What is the instrument used to measure lens thickness
Caliper
___________ measures the distance between the back surface of a lens and the front surface of the cornea (on a closed eyelid)
Distometer
The average eye lis is how thick?
1mm
Lens power is affected by vertex distance, to compensate for effective power lens change a new lens power must be determined. VDCC consists of _______ wheels joined together at their centers of rotation.The ________ inner wheel contains two metric scales 1 for plus, 1 for minus lenses. The _______ outer wheel contains a dioptic scale, can also be calculated using a formula
1 - two
- Smaller
- Larger
