BSO 221

Dispensing OpticsGenalin A. Ang O.D.

Practical Exercise

• Check the horizontal alignment• Look at the spectacles from in front of the

patient to ensure that it looks horizontal. If the spectacles are marked up, either in preparation for height measurement or with progressive lens marking on delivery of new spectacles, check that the fitting crosses are correctly aligned.

• Check the facial wrap (dihedral angle)• Look at the spectacles from above the patient.

Check that the frame front follows the face. Make sure that it is not too f lat. The facial wrap is normally about three to five degrees.

The Bridge Width

• The bridge width is the minimum horizontal distance between the nasal surfaces of the rims on a plastic or metal frame, or the minimum horizontal distance between the nasal surfaces of the lenses in rimless frames.

• If a frame has adjustable nose pads on metal arms various modifications can be made in order to achieve a satisfactory fit;

The frontal angle

• is best viewed from the front, go figure. It is the angle that is closer at the top and wider at the bottom.

• This angle can usually be adjusted using nose pad pliers or a pair of snipe nose pliers.

• All that needs to be done is to match the angle of the nose as it widens.

• The splay angle is viewed while looking through the spectacles. The splay angle is the angle that increases or decreases the amount of nose pad surface that faces you.

• Individuals who have shallow bridges on their nose tend to require more splay .

• : Check the pantoscopic tilt• Look at the spectacles from the patient's

temple. The pantoscopic tilt is the angle between the spectacle plane and a line perpendicular to the f loor. Most lenses require a pantoscopic tilt between eight to 12 degrees. Use angling pliers to adjust the tilt.

• Pantoscopic tilt is when you bend the temples so that the lower part of the frame sits closer to the face than the top. Most progressive manufacturers suggest between 8 - 12 degrees of pantoscopic tilt.

• There is also a correspondence between placement of the optical centre of a lens and the amount of tilt needed to avoid inducing cylinder.

• Every 2 degrees of tilt is equivalent to decentring the optical centre up a millimetre.

• Check the temple width• Look again at the spectacles from above the

patient. Ensure that the temples do not exert pressure against the side of the head in front of the top of the ear.

• Check the temple bow• While looking from above check that the

temples follow the side of the head without touching or exerting pressure until they reach the top of the ear.

•

• Check the length to bend• Look behind the patient's ear. The bend

should start just after the top of the root of the ear.

• The arm length is measured from the dowel point to the extreme end of the side, this is made up of the length to the bend and the length of the drop to give the overall length of side.

• When choosing a new spectacle frame check your current frame sizes by looking for the printed measurements (usually found on the arm or bridge), for example:

52-16-13552 (mm) will represent the lens width16 (mm) will represent the bridge width135 (mm) will represent the overall length of the arm