Basic Eyeglass Terms

Question 1

Eyewire

Answer 1

The part of the frame front that surrounds each lens and holds the lens in place.

Question 2

Bridge

Answer 2

Frame that connects the two eyewires together and supports the frame on the patient’s nose

Question 3

Hinge

Answer 3

-Connects the frame front to the temples.
-Allows the temples to fold in behind the frame front so that the eyeglasses will occupy less space and fit into a case or pocket.

Question 4

Nosepads

Answer 4

-Located on the eyewire, near the area where the bridge is attached.

-distribute the weight of the frame onto the sides of the nose to make the frame more comfortable to wear. -

-proper adjustment of the nosepads is critical to the fit of the frame and comfort of the wearer.

Question 5

Temples

Answer 5

Extend from the frame front, back alongside the head, and over the ear of the wearer. Temples are made up of the butt portion, dowel hole, shield, bend, and earpiece.

Question 6

Boxing System

Answer 6

Gives frame dimensions in a consistent manner, regardless of the shape of the frame.

Question 7

“A” Measurement

Answer 7

-Width of lens or Eye size.
-Widest horizontal dimension of the lens opening, as measured from the tips of the eyewire grooves.
-Measured in millimeters.
-Measure lens only don’t include frame.

Question 8

“B” Measurement

Answer 8

Height of lens or frame height

-Most vertical dimension of the lens opening
-As measured from the tips of the eyewire grooves.
-Measure lens only don’t include frame.

Question 9

Effective Diameter (ED)

Answer 9

Gives largest diameter through the lens (think of it as the largest circle that can enclose the lens). May be taken in any direction.

It is two times the length of the longest radius that fits inside the eye wire opening.

Measurement can be used to determine what size lens blank must be used in order to have the lens fit the frame since it represents widest part of lens.

Question 10

Distance Between Lenses (DBL)/ Bridge Size

Answer 10

Represents distance separating the two lenses.

-Measured at the part of the frame at which the distance between lenses is the smallest.
-The eyesize and DBL measurements are usually stamped on the frame. (Ex: 48/18. 48 is the eyesize in millimeters and 18 is the DBL or bridge size in millimeters).

Question 11

What does the box mean in between eye size and DBL/ Bridge Measurement?

Answer 11

Indicates measurements were made using the boxing system of frame measurement.

Question 12

Prentices Rule Formula (calculating prism)

Answer 12

Prism (diopters)=Decentration (in centimeters) x Power (diopters)

Or

P=hcm x D (remember to convert h from millimeters to centimeters by diving h by 10)

The prism power of a lens at any point on its surface, in prism diopters, is equal to the distance away from the optical center (h) in centimeters times the power of the lens in diopters.

Question 13

Determining prism direction

Answer 13

If plus lens it will be on 90 degree meridian.

-direction options would be BU,BD or a combo.

If minus lens it will be on 180 degree meridian.

-direction options would be BI, BO or a combo.

BU/BU, BD/BD, and BI/BO all have canceling effects (so subtract numbers from each other and only list the eye with stronger power and indicate corresponding direction)

BU/BD, BI/BI, and BO/BO all have compounding effects (so add numbers together and list each eye with corresponding direction)

Question 14

Calculating Total Decentration

Answer 14

-Frame PD minus the Patient PD= Total Decentration in mm.
-Then divide Total Decentration by 2 since there are two lenses.

(Ex: Frame PD 56 and Patient PD 52.
56-52= 4 mm Total Decentration.
4mm/2= 2mm Decentration per lens.)

Question 15

Decentration

Answer 15

Refers to how far the optical centre needs to be moved to be directly in front of the patient’s eye. Need Frame PD to do this.

Question 16

Optical Center (OC)

Answer 16

“Sweet Spot” in lens which provides truest vision. Located slightly above geometric center. Based on pupil alignment in a lens.

Question 17

Calculating Frame PD

Answer 17

= “A” Measurement (Eyesize)+ DBL

Question 18

Calculating Minimum Blank Size

Answer 18

Absolute smallest lens blank that can be used to edge a lens.

ED + 2x Decentration + 2=minimum blank size.
(Ex: R eye ED 55, 4mm Decentration and L eye ED 55, 2mm Decentration
R eye- 55 + 8 + 2=65 mm MBS
L eye- 55 + 4 + 2=61 mm MBS)

Question 19

Geometric Center

Answer 19

Physical center of the lens not based on pupil position. Can be determined by taking half of “A” measurement and half of “B” measurement. Where they meet is GC.

Question 20

Frame Front

Answer 20

-The main part of your glasses frame. -helps secures your lenses in place (eye wire).
-largely dictates the style and aesthetic of your glasses.

Question 21

How to Flat Transpose an RX from 180 degrees to 90 degrees

Answer 21

1.)Subtract the sphere power from the cylinder power to arrive at the new sphere power.

2.) Subtract 90 degrees from the axis

Question 22

How to Flat Transpose an RX from 90 degrees to 180 degrees

Answer 22

1.) Add the sphere power to the cylinder power to arrive at the new sphere power.

2.) Change cylinder sign

3.) Add 90 degrees to the axis