Lens / Frame Considerations
08-2008
 Lenses correct a patient’s vision and the benefits that each lens design provides, is important to patients. A single vision lens can be used for far or near vision but only has one power that is useful. For a +2.50 add presbyope, a bifocal would provide two powers, only distance and near vision while a progressive delivers an infinite number of powers i.e., clear vision at all distances, from far to near. The series of illustrations (Fig. 1) describe useful distances of clear vision.
Single vision, progressive and lined multifocal lenses are described by segment shape and size. Multifocals, lenses with more than one focus, are available in a variety of styles. Progressives come with multiple corridor lengths so that they can fit into smaller frames and still provide excellent far to near vision. Progressives are the most popular option of multifocals available today. The older style of multi-focal lens, the bifocal is referred to as a flat top and is available in 28mm width; bifocals are also available as flat top 35s, round segments, blended round segs and executives. In trifocals, there are three zones of vision and are described by the height of the mid-range portion and the width of the segment. For example, available sizes are FTT 7x28 and FTT 8x35. Call your laboratory for a complete list of available multifocal lens styles.
 Boxing System
A - Eye size - The horizontal width between the two
vertical lines tangent to the edges of a lens—or a box enclosing the lens (Fig. 2). Be sure to consider the depth of the bevel when measuring the frame.
B – Eye Height - The vertical height between the two horizontal lines tangent to the edges of the lens—or a box enclosing the lens. Be sure to consider the depth of the bevel when measuring the frame.
DBC - Distance between centers; the distance between the geometric centers of the right and left lens openings.
DBL – Bridge size; the minimum distance (nasal) between the two lenses or frame openings.
ED – Effective Diameter; twice the longest radius from the geometric center of lens to the farthest edge; the smallest circle that will completely enclose the lens.
G - The geometric center of an imaginary box enclosing the edges of a finished lens or opening in a frame ( 1/2 B and 1/2 A measurements).
Lens Definitions
Decentration – The horizontal distance (mm) that the OC is moved from the GC to place the OC in line with the visual axis; in towards the nose or out, towards the ear. In SV, bifocal and trifocal lenses, the OC is typically located on the mid-line vertically.
Inset – The horizontal distance (mm) from the OC to the segment center.
Fitting height – The location of the segment top in bifocals and trifocals or the fitting cross in progressives. Height is measured in mm from the lowest position on the lens (edge of the lens) to the top of the segment or fitting cross.
 Progressive Lens Engravings – Semi visible engravings that allow remarking and positioning of the fitting cross of the lens. They are composed of two circles 34mm apart, 17mm to either side of PRP.
Progressive Lens Ink Markings – Temporary inked markings used to correctly locate the fitting cross and 180º axis for processing as well as confirming correct lens-in-frame positioning.
Each manufacturer provides a unique set of semi-visible engravings and ink marks that can help the optician identify which lens a patient is wearing. These engravings tell the manufacturer, lens design, add power and material that the lens is made from. Use them to know which lenses might need to be replaced or the lenses that a patient has been wearing.
Be sure to have a complete set of lens descriptions from the manufacturer; they describe markings and logos used. Also, ask your laboratory for a OLA Progressive Lens Identification book. It lists all the lenses available and shows their markings.
What Would You Do?
PATIENT SITUATIONMr. Travers just came in and wants to order another pair of progressives just like the ones he is wearing; same frame also. You’ve only been working in the office for 4 weeks. The optician has asked you to record the frame size, lens style and prescription. What do you do? SOLUTIONSimple, take a breath and ask Mr. Travers for his glasses so that everything that he likes about them can be verified, tell him to have a seat for a few minutes while the order is recorded and do the following. Give him a brochure on polarized sunwear so he can read about that pair of glasses he was interested in last time (there was a note in his file).
- Pull the patient’s record so that everything about his glasses can be checked so they are duplicated exactly.
- Measure the frame A, B and DBL. Record it on the order, check that this is the same that was ordered last ti
me.
- Verify that the lenses are Varilux Physio progressives – look for the engravings. They will confirm Varilux Physio.
- Look in the patient’s record and confirm that the prescription was correct last time so it can be ordered again.
- Last time Mr. Travers ordered Transitions. Be sure that they are ordered again also.
- Don’t forget the AR. You might suggest to Mr. Travers that there is a new Crizal and since he was so happy last time with the improvement – he might want to upgrade to Crizal Avancé with Scotchgard protector Lenses.
Complete the written order, clean the glasses and ask the optician to return the glasses and be sure that they are in good adjustment.
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