Basic Eyeglass Adjustment Terms

Question 1

Fitting Triangle

Answer 1

A picture representation of the pressure points between an eyeglass frame and the overhead view of the patient’s head.

Goal during adjustment process is to equalize the pressure of the frame over the bridge of the nose and the widest part of the head on each side of the ears.

Question 2

Frame Height

Answer 2

Determined by the height of the frame (“B” measurement) and the way in which the frame rests on the wearer’s nose. If the frame has adjustable nosepads, the frame height can be altered somewhat. However, if the frame has a fixed bridge, the frame height is determined during the frame selection process

Question 3

Vertex Distance

Answer 3

Distance from the back of the lens to the cornea. Generally, we do not measure the vertex distance except in high prescriptions (more than 6 diopters), but when fitting the frame to the patient’s face, you want to be certain both lenses rest an equal distance from the eye.

Question 4

Face Form

Answer 4

The way the frame front follows the contour of the face. Generally, the frame front protrudes slightly at the nose and is farther back near the temples. Some frames (such as wrap-around sunglasses) have a high degree of face form, with the bridge of the frame resting substantially forward of the hinge on the frame front.

The amount of face form can be assessed by taking the frame with the temple extended and placing a ruler against the back of the frame front from the outside edge of one eyewire to the outside edge of the other eyewire. The ruler will be straight and the amount of curve to the frame front will show the amount of face form.

Question 5

Pantoscopic Angle/ Tilt

Answer 5

Refers to the angle the temple of the frame makes with the frame front. When the frame is on the wearer, the bottom of the eyewire should be closer to the cheeks than the top of the eyewire is to the eyebrows. A small amount of pantoscopic angle is needed for the wearer to achieve the proper optics through the lenses and have the widest possible field of view through multi-focal lenses.

Question 6

Retroscopic Angle/ Tilt

Answer 6

Angle the temple makes with the frame front when the bottom eye wire may be positioned away from the cheek.
Not desirable.

Question 7

Temple Adjustment

Answer 7

Temple bends should begin
at the top of the ear. The end of the temple should be bent at a 45-degree angle and bent in so that its flat side touches the skull, behind the ear.

Question 8

Interpupillary Distance Rule

Answer 8

Used to make sure the frame front is even. Lay your PD rule across the ocular side of the frame front, just below the temples at the endpiece. When the PD rule is touching both endpieces, it should be equidistant from the frame at its two nasal points, just above the nosepads. This is also known as vertical alignment or four-point touch