Before reading this section please brush up on spectacle skills to make sure that you know how to transpose.
The automated lensometer is a lensometer that does all of the work for you. Just line of the lens then the machines
beeps and spits out the reading. As long as you have selected the correct cylinder type you can’t really go wrong.
Advantages to using the automated lensometer
It eliminates math errors
It reads progressive lenses with ease
The manual lensometer requires more skill than the auto lensometer. It is used for reading all types of glasses and is
necessary when determining the prism.
Steps in using the Manual Lensometer
Adjust the eye piece until the target is clear
Position the glasses with the bottom of the frame against the frame stage.
Center the target (where the lines intersect)
Focus the narrow lines (single lines) and read the power wheel. This gives the spherical power.
Focus the wide lines (triple lines)and read the power wheel.
Read the Axis wheel
If the lens is in the incorrect cylinder you can either transpose the prescription or re-read the lenses and rotate, but
rotate the lens 90 degrees.
To get the prescription you will need to know the sphere, cylinder, and axis.
Sphere = narrow lines
Cylinder = wide lines – narrow lines
Axis = read the axis wheel
Lets do an example:
The narrow line is in focus at -1.00. The wide line is in focus at -3.00. The axis is on 084. What is the prescription?
Answer:-1.00 -2.00 x 084
If you have glasses that have add power such as bifocals and trifocals then move the frame stage up until the mires
appear in the center. The only change will be a change in the sphere, the narrow lines. For example:
The spherical power is -1.00. When you move the frames up and focus the mires you read +1.50. What is the add power?
Have you ever had the test where the doctor asks you when one line is over the other? The doctor is seeing if you need
prism in your glasses. This is common for patients who complain of binocular double vision, which is caused by the
inability of the eyes to focus on the same point. When prism is added to your glasses it is like the added a small wedge
to your normal prescription which will help your eyes focus on the same point thereby getting rid of the double vision.
This is how you find prism with the lensometer.
While the patient is wearing their glasses mark where their pupils are with a dry erase marker. This mark is where you should center your glasses on the lensometer.
If they have prism and your lens is centered correctly you should see then the lines a slightly off center.
Count how many rings from the center the lines are.
This is how you would read the lines
If the lines are 3 rings temporally from the center you would say that the prism is 3 base out.
If the lines are 3 rings medially from the center you would say that the prism is 3 base in.
If the lines are 3 rings superiorly from the center you would say that the prism is 3 base up.
If the lines are 3 rings inferiorly from the center you would say that the prism is 3 base down.
It could also be that the lines can be a combination of two directions. Here as an example:
If the lines are 2 rings temporally and 1 ring superiorly what would the prism be.