Question 1

During a lensometer examination, if the examiner is severely astigmatic, they should:

Accepted Answer

During a lensometer examination, if the examiner is severely astigmatic, they should wear their glasses. The instrument's reticle does not correct for the examiner's astigmatism and it is crucial that the reticle adjustment is correct in order to obtain accurate measurements.

Question 2

What does it mean when the mires cannot be centered in the lensometer?

Accepted Answer

If the mires cannot be centered in the lensometer, it means the prism has been ground into the lens. To compensate for this, the reticle contains concentric circles that can be used to measure small amounts of prism. There may also be a dial at the opposite end of the reticle carrier that measures higher amounts of prism.

Question 3

Which is a handheld instrument that measures the surface power of a spectacle lens in diopters?

Accepted Answer

The Geneva Lens Clock is a handheld instrument that measures the surface power of a spectacle lens. A lens clock measures the curvature of a surface, but gives the result as an optical power in diopters, assuming the lens is made of a material with a particular refractive index.

Question 4

Vertex distance can be measured with a:

Accepted Answer

Vertex distance can be measured with a distometer. The vertex distance is the distance from the cornea of the patient's eye to the lens inserted in the trial frame, refractor, or glasses.

Question 5

Which answer below can be measured by a lensometer?

Accepted Answer

A lensometer can measure the prescription, record the center of the prescription, measure the add power and find the prism amount in the lens.
Two additional measurements that are important to the prescription might also be the base curve and center thickness, both of which are measured using other instruments.

Question 6

Vertical and horizontal prism is measured in a lensometer by:

Accepted Answer

Vertical and horizontal prism is measured in a lensometer by seeing that the mires in the lensometer are both off set from the center of the grid.

Question 7

Do you read the cylinder power first or the sphere power first in a lensometer?

Accepted Answer

To read a prescription in a lensometer you read the sphere power first then the cylinder power.
To read the sphere power first you will need to turn the power of the wheel to its highest plus power, put the lens on the seat of the lensometer facing to you. You must move the lens back and forth to line it up to the center of the mire while slowly turning the hand wheel toward you to determine the sphere power. This is found when the line is in focus to you. Put the pressure piece on the lens to keep it in place. Read the wheel. This is the sphere power. If just the one mire is clear then you know the lens has astigmatism, so continue turning the wheel until the next mire come into focus while at the same time rotating the axis wheel. Read this power on the wheel. Subtract the second reading from the first to get the cylinder power for that lens. Note the axis.

Question 8

You can use the lensometer to help find the pupillary distance of the lenses.

Accepted Answer

A lensometer can help you to determine the pupillary distances of the lenses.
When you spot the centers of each lens in the lensometer, take the frames out of the lensometer, and using your PD ruler, measure the distance between the spots on both lenses. This will give you the distance PD measurement.

Question 9

A lensometer can read up to how many diopters of prism without using additional prism rings?

Accepted Answer

The lensometer can read up to five diopters of prism without the need for additional prism rings to determine higher prism amount.
If you find that the prism is more than five, you can add prism rings to the prism compensating device knob. You will need to rotate each lens you put in to be able to see the correcting prism.

Question 10

Which instrument measures the curvature of the surface of a lens? Choose all that apply.

Accepted Answer

The curvature of the surface of a lens can be determined by a using a spherometer, more commonly known as a lens clock.
This instrument measures the base curve of the lens reading the black numbers when all three points are touching the lens.
The inside surface of the lens can also be measured with this instrument. The reading for the inside uses the red markings on the face of the lens clock.
In addition the cylinder of a lens can also be read by reading the inside of the lens, rotating the lens and noting the high and low reading. The difference between the two is the amount of cylinder power in the lens.

Question 11

What measures the thickness of a lens up to 19 mm?

Accepted Answer

The thickness of a lens can be measured with a lens thickness caliper instrument.
This instrument can measure up to 19 mm of thickness. The throat has a maximum depth of 3.8 and calibrated in .20 increments. This device is only made to measure the thickness of lenses.

Question 12

The first step in using a lensometer to check glasses is to?

Accepted Answer

The first step in using a lensometer to check glasses is to calibrate the eye piece for you.
To calibrate, set the focus wheel to plano. Then turn the eyepiece counterclockwise as far as it can go. Carefully, as you are looking in the eyepiece, turn the eyepiece back slowly until you see the target mire is clear and focused. Note where the index spot is and use this setting each time you use the lensometer.
This is done because you may have a slight eye error, which will affect the way you see the mires in the lens.

Question 13

If you have the following prescription, how would you use the lensometer to read it in minus cylinder?
Prescription: -2.00 +3.00 X 65

Accepted Answer

To read the prescription -2.00 +3.00 X 65 in minus cylinder you would first transpose the prescription into +100 -3.00 X 155.
Then go to the axis adjustment wheel and place it at 155, turn the power drum to plus. Begin to bring the power wheel toward you to find the sphere power at +1.00 and keep turning to see the second set of mires focus in on -2.00 to give the power for the cylinder of
-3.00.

Question 14

Is it necessary to verify the intermediary section of a trifocal in the lensometer?

Accepted Answer

No, it is not necessary to verify the intermediary section of the trifocal in a lensometer.
The intermediary section is always half the bifocal strength and is never verified.

Question 15

What is another word for a lens clock?

Accepted Answer

The more technical term for a lens clock is a spherometer.
It is used to determine base curves, back side curves and cylinder power.

Question 16

You would need to set a pupilometer to which setting to get the patient's PD for 16 inches?

Accepted Answer

You would need to set the pupilometer at 40 cm to get the patient's PD for 16 inches.
You would set distance wheel to infinity (?) for far PD or the correct near distance 35 cm=~14 inches and 45 cm=~18 inches.

Question 17

Which feature(s) is(are) best to have in a pair of pliers to make sure you won't damage a frame's finish when adjusting? Choose all that apply.

Accepted Answer

The best features to have in a pair of pliers you will use to adjust a patient's frame are a protective plastic jaw and rubberized handles to prevent your hand from slipping and marring the frame.
There are several on the market that do not have these features. If you do not have access to them, be especially cautious that you do not damage the frame when adjusting it.

Question 18

Angling pliers are used to:

Accepted Answer

Angling pliers are specifically made to adjust the frame's panoscopic angle.
The panoscopic angle adjustment is done by adjusting the temples so that the frame either moves away from the face at the bottom or toward the face at the bottom. This heavy duty tool is created to grip the end piece firmly in order to do the adjustment.

Question 19

A distometer measures the distance between the eyes.

Accepted Answer

A distometer measures the vertex distance between the back of your lens and the front of your cornea.
Vertex distance can play a major role in adaptation for a high powered lens wearer. Generally, vertex distances should be within 8-12 mm. If a patient is picking out an entirely new frame design and has a high power prescription, double checking the vertex distance before ordering will catch potential problems.

Question 20

Hot air warmers should not be used for which frame types?

Accepted Answer

Hot air warmers should not be used for metal or SPX frames.
Metal frames can be bent and adjusted without heat. SPX frames will heat, but as soon as they cool they will shrink and cannot be restored to their normal shape and size.

Quiz 2: Instrumentation