Lensometer

Question 1

What other names does the lensometer have?

Answer 1

• Focimeter
• Vertometer
• Lens meter

Question 2

What does the lensometer do?

Answer 2

It allows us to inspect the lenses for total diopter power, add power, axis and lens alignment, optical center placement and prismatic effect

Question 3

What are the major parts of a lensometer device?

Answer 3

• Eyepiece
• Marking device
• Prism dial
• Lens table
• Table control lever
• Lens holder

Question 4

What does the power wheel used for on a lensometer?

Answer 4

Used to find the power of the lens and it is marked with powers rang from -20 to +20 diopters

Question 5

What is the elevation lever used for on a lensometer?

Answer 5

It changes the angle of the lensometer

Question 6

What is the axis wheel used for on a lensometer?

Answer 6

The axis wheel is the large wheel marked from 0 degrees to 180 degrees that is used to find the axis location on the lens.

Question 7

What is a reticle/target?

Answer 7

• It is a prism scale with a series of circles where the mires are focused and marked.
• It’s used to center the lens for marking or verification of power

Question 8

What is it called when there is a set of three thin, closely spaced lines?

Answer 8

Sphere lines

Question 9

What is it called when there is three widely spaced lines?

Answer 9

Cylinder lines

Question 10

What do you do to prepare the lensometer before determining the power of the lens?

Answer 10

• Turn the power wheel to the highest plus or the most minus position
• Turn eyepiece counterclockwise so target is out of focus
• Slowly turn the eyepiece in the clockwise direction until the target is in sharp focus
• Do not turn eyepiece back and forth
• Rotate power drum until mires are in focus
• Power drum should be at zero or plano

Question 11

What do you do to read or neutralize a single vision lens prescription?

Answer 11

• Adjust lens table so concave side of lens is centered against lens stop vertically and horizontally
• To reposition, lift lens holder before moving lens
• Never slide lens against the lens stop!
  Look at target through eye piece
• Move lens table until optical center is in center of target

Question 12

What do you do to find the spherical lens on the lensometer?

Answer 12

• Move the power drum until the sphere lines are in sharp focus at most plus power on the drum
• Read the power of the lens from the side of the instrument
• Make sure to include “+” or “-” signs
• “D.S.” for diopter sphere
• “Sph” for sphere

Question 13

What are the powers noted in eighths of a diopter?

Answer 13

0.00
0.12
0.25
0.37
0.50
0.62
0.75
0.87

Question 14

If both sets of lines come to focus at +2.00D. What is the power noted as?

Answer 14

The power is noted as +2.00DS

Question 15

What is spherocylindrical?

Answer 15

• If both sets of lines are not in focus at the same time, the lens is spherocylindrical
• If lines appear broken, rotate the cylinder axis wheel until sphere lines are in focus and a solid line
• If the cylinder lines are the first to come into focus, turn the axis wheel by 90 degrees to begin reading the power

Question 16

What is important to remember about the power wheel?

Answer 16

• The cylinder power is not the number you read from the power wheel.
• Instead, it is a difference between the sphere reading and this final reading

Question 17

What happens when the first reading sphere power is -2.00D and the second reading power is -3.00D?

Answer 17

The two reading power is -1.00D

Question 18

What do you do after determining the cylinder power?

Answer 18

Read the cylinder axis from the axis wheel at the back of the lensometer

Question 19

The sphere power is +1.00D and the cylinder measures on the lensometer at -1.50D. Now, what is the cylinder power?

Answer 19

The cylinder power is -2.50D

Question 20

What do you do first when measuring the bifocal segment?

Answer 20

• Place the distance, convex surface against the lens stop
• Focus vertical target lines
• Rotate axis wheel to make sure lines are unbroken
• Note power
• Move bifocal segment in front of the lens stop
• Focus the same set of lines
• Note power

Question 21

What do you do to specify the progressive design on lens?

Answer 21

• Place the front surface on the chart
• Lines up dots
• Draw in markings
• Follow the same steps as a bifocal lens

Question 22

What do you do to the lens to get a prism prescription?

Answer 22

A prismatic prescription is centered when the mires are located on the indicator rings at the point that matches the prescribed prism

Question 23

What do you do on the lensometer to verify a high amount of prism?

Answer 23

Use the prims dial compensating device

Question 24

How do you use the prism dial?

Answer 24

• Dot the monocular PD measurement
• Place the dots over the lens stop
• Dial in sphere and axis power of Rx
• Estimate if horizontal or vertical prism is greatest
• Move knob on prism compensating device to position prism base at 180 degrees if the horizontal prism is larger or 90 degrees if the vertical prism is larger.
• Move internal illuminated target onto horizontal or vertical crosshair
• Turn knob on the prism device to increase or decrease prism amount
• Read a larger amount from the external prism device
• Read a smaller amount from the internal indicator

Question 25

How do you estimate if a horizontal or vertical prism is on the lensometer?

Answer 25

Look at the thickness difference between the temporal and nasal edges, and top and bottom edges, and find the thickest edge

Question 26

When looking through the eyepiece of the lensometer, when the three closely spaced lines and three widely spaced lines do not come into focus at the same time, the lens is what?

Answer 26

Spherocylindrical

Question 27

When looking through the eyepiece of the lensometer, when the three closely spaced lines and three widely spaced lines come into focus at the same time, the lens is what?

Answer 27

Spherical lens