Lensometer Flashcards
What other names does the lensometer have?
- Focimeter
- Vertometer
- Lens meter
What does the lensometer do?
It allows us to inspect the lenses for total diopter power, add power, axis and lens alignment, optical center placement and prismatic effect
What are the major parts of a lensometer device?
- Eyepiece
- Marking device
- Prism dial
- Lens table
- Table control lever
- Lens holder
What does the power wheel used for on a lensometer?
Used to find the power of the lens and it is marked with powers rang from -20 to +20 diopters
What is the elevation lever used for on a lensometer?
It changes the angle of the lensometer
What is the axis wheel used for on a lensometer?
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.
What is a reticle/target?
- 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
What is it called when there is a set of three thin, closely spaced lines?
Sphere lines
What is it called when there is three widely spaced lines?
Cylinder lines
What do you do to prepare the lensometer before determining the power of the lens?
- 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
What do you do to read or neutralize a single vision lens prescription?
- 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
What do you do to find the spherical lens on the lensometer?
- 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
What are the powers noted in eighths of a diopter?
0.00
0.12
0.25
0.37
0.50
0.62
0.75
0.87
If both sets of lines come to focus at +2.00D. What is the power noted as?
The power is noted as +2.00DS
What is spherocylindrical?
- 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
What is important to remember about the power wheel?
- 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
What happens when the first reading sphere power is -2.00D and the second reading power is -3.00D?
The two reading power is -1.00D
What do you do after determining the cylinder power?
Read the cylinder axis from the axis wheel at the back of the lensometer
The sphere power is +1.00D and the cylinder measures on the lensometer at -1.50D. Now, what is the cylinder power?
The cylinder power is -2.50D
What do you do first when measuring the bifocal segment?
- 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
What do you do to specify the progressive design on lens?
- Place the front surface on the chart
- Lines up dots
- Draw in markings
- Follow the same steps as a bifocal lens
What do you do to the lens to get a prism prescription?
A prismatic prescription is centered when the mires are located on the indicator rings at the point that matches the prescribed prism
What do you do on the lensometer to verify a high amount of prism?
Use the prims dial compensating device
How do you use the prism dial?
- 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
How do you estimate if a horizontal or vertical prism is on the lensometer?
Look at the thickness difference between the temporal and nasal edges, and top and bottom edges, and find the thickest edge
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?
Spherocylindrical
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?
Spherical lens
