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16 Frames types and materials
Optometry and Vision Sciences (The University of Lahore)
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FRAME TYPES AND MATERIALS
AUTHOR
David Wilson: Brien Holden Vision Institute (BHVI), Sydney, Australia
PEER REVIEWER
Mo Jalie: Visiting Professor: University of Ulster, Varilux University in Paris
THIS CHAPTER WILL INCLUDE A REVIEW OF:
•
Spectacle Frames – Introduction
•
Common Frame Materials (plastic)
•
Common Frame Materials (metal)
•
Manipulation of Spectacle Frames
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Frame Types and Materials
SPECTACLE FRAMES - INTRODUCTION
SPECTACLE FRAMES
Figure 16.1: Spectacle frames
METAL FRAMES
PLASTIC FRAMES
COMBINATION FRAMES
RIMLESS MOUNTS
Metal frames are made entirely of metal (with the minor exceptions of the nose pads and
the temple end-pieces). They support the lens in a grooved eye-wire which must be
opened at a joint to insert the lenses. Metal frames have the benefits of light weight,
limited interference with field of view and durability.
Plastic frames are made from a number of modern thermoplastics (discussed in the next
section). The plastic eye-wires also hold the lenses in by way of a groove but the lenses
are generally inserted by heating and stretching the plastic or by stretching it cold. Plastic
frames, although thicker and generally heavier than the finer metal frames, are more
colourful and offer a greater variety of styles.
Combination frames use both metal and plastic in varying amounts. They usually have
metal eye-wires with plastic trims and plastic sides.
Rimless mounts are so called because they don’t “frame” the lenses. The two main types
of rimless mounts include nylon frames (also known as supra frames) and drilled rimless
mounts. Nylon frames hold the lenses in by a nylon cord which holds the lens in place by
a groove that is edged into the lenses. Drilled rimless mounts on the other hand have
screws inserted through holes that are drilled through the lenses.
Speciality frames are designed for a specific purpose and not for general wear. They
include:
Sports (Athletic) Spectacles
Sports frames are normally made of nylon or a similar material and have soft silicon pads
on the bridge and temple.
Lorgnettes
Lorgnettes have a handle attached to a frame front and no temples (Figure 16.2a). They
are designed to be held up in front of the eyes for reading. They are seldom used now.
Ptosis Frames
Ptosis frames have a wire or plastic crutch attached to the top eye-wire to support the
drooping eyelid (Figure 16.2b).
SPECIALITY FRAMES
Make-Up Spectacles
Make-up frames allow each eye-wire to be swivelled up or down independently to allow
access to one eye to apply cosmetics or insert a contact lens while using the other eye
(Figure 16.2c).
Figure16.2: (a) Lorgnettes (b) Ptosis frame (c) Make-up spectacles
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Frame Types and Materials
COMMON FRAME MATERIALS – PLASTIC
Cellulose acetate is a clear thermoplastic polymer (Figure 16.3). Cellulose acetate was
the most popular material for over 20 years, replacing the more dangerous, flammable
material, cellulose nitrate. Acetate is produced in pre-coloured sheets and the frames are
then cut from these sheets using various cutting jigs. There are about 130 steps in
producing a plastic frame from acetate since each part must be cut separately. Metal
cores are inserted in the temples to provide greater strength.
Following the cutting process, the frame fronts and temples are polished by rotating them
in large barrels mixed with polishing compounds. After barrelling they are assembled,
buffed and put into standard alignment.
Advantages
•
Low flammability
•
Easily polished
•
Colour fast
•
Easily repaired
CELLULOSE ACETATE
Disadvantages
•
Will blister if overheated
•
The frames will tend to return to their flat state if overheated
•
Plasticisers will cause the frame to deteriorate over time
•
Frames will become brittle with age
•
Frames may be damaged by solvents
To make any adjustment, cellulose acetate should be heated to about 70°C and then
manipulated only when soft.
Figure 16.3: Cellulose acetate frame material
Cellulose propionate is also a thermoplastic material, softening with heat (Figure 16.4).
Cellulose propionate frames are produced by a forced injection moulding process. Fewer
steps are required in the production of cellulose propionate frames and there is less
wastage since there are no off-cuts.
CELLULOSE
PROPIONATE
Cellulose propionate has become the material of choice for many manufacturers since it
is much cheaper to produce. Propionate is made by injection moulding and is coloured
after production. Like acetate, propionate frames have metal cores in the temples,
inserted into the mould before moulding the frame.
Following the injection and colouring process, the frame fronts and temples are polished
by rotating them in large barrels mixed with polishing compounds. After barrelling they are
assembled, buffed and put into standard alignment.
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Frame Types and Materials
COMMON FRAME MATERIALS – PLASTIC (cont.)
Advantages
•
Slightly lighter than acetate
•
Low flammability
•
Inexpensive to produce
•
Easily polished
•
Can be made thinner than acetate frames
Disadvantages
•
Will blister if overheated
•
Plasticisers will cause the frame to deteriorate over time
•
Frames will become brittle with age
•
Colour can be buffed off with excessive buffing
•
Frames may be damaged by solvents
CELLULOSE
PROPIONATE (cont.)
Cellulose propionate requires more heat than cellulose acetate.
Figure 16.4: Cellulose propionate frame material
Polyamide, meaning more than one amide, is an organic compound of the nylon family.
Polyamide has considerable mechanical stability and can be made even thinner than
propionate.
Polyamide is produced in a similar fashion to propionate.
POLYAMIDE
Advantages
•
Lighter than acetate
•
Hypoallergenic
•
Low flammability
•
Very hard, durable surface
•
Can be made thinner than other plastic frames
Disadvantages
•
Will shrink if overheated
•
Cannot be repaired
Polyamide is easily affected by heat and is best fitted cold.
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Frame Types and Materials
COMMON FRAME MATERIALS – PLASTIC (cont.)
Optyl is a thermoelastic material, but unlike the other plastics covered so far, it has a very
powerful memory and will always return to its original shape with heat (Figure 16.5). Its
remarkable memory makes Optyl a unique frame material, despite being produced in a
similar way to other injection moulded materials. Optyl also has considerably greater
durability than other frame materials.
Optyl can be heated to a higher temperature than other plastics and prefers more, rather
than less, heat.
Advantages
•
Lighter than all other plastic frame materials
•
Hypoallergenic
•
Low flammability
•
Very hard, durable surface
•
Will not age (due to a lack of plasticisers)
OPTYL
Disadvantages
•
Will return to its original shape if overheated, losing any adjustment
•
Cannot be repaired
Optyl requires considerable heat, greater than 90°C and should not be manipulated cold.
Figure 16.5: Optyl frame material
Nylon is a very tough frame material and, for this reason, it is used in protective
spectacles and sunglasses where they receive rough treatment. They are however much
more difficult to adjust and are not as attractive as other materials.
NYLON
Advantages
•
Lightweight
•
Strong and flexible
•
Low flammability
•
Not affected by heat and cold
Disadvantages
•
Poor surface quality
•
Very difficult to adjust
It is difficult to fit lenses to a nylon frame. Nylon should be cold when fitted with lenses.
For adjustments, it is possible to heat nylon in hot water (no other material should be
heated this way).
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Frame Types and Materials
COMMON FRAME MATERIALS – PLASTIC (cont.)
Carbon fibre is a very tough, yet brittle frame material (Figure 16.6). It is made from nylon
mixed with a fibre of potassium titanate. As with nylon, carbon fibre frames are difficult to
adjust and should be cold when fitted with lenses. The inclusion of visible fibres also
requires opaque colours.
Advantages
•
Lightweight
•
Good shape retention
•
Strong
•
Low flammability
CARBON FIBRE
Disadvantages
•
Difficult to adjust
•
Brittle when dropped
•
Not available in transparent colours
Figure 16.6: Carbon fibre frame material
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Frame Types and Materials
COMMON FRAME MATERIALS – METAL
Gold filled (rolled gold) frames have the gold (normally 10 karat) wrought over the base
metal (usually a nickel based alloy) before the metal is fashioned into a frame
(Figure 16.7). This frame type has the greatest amount of gold and is the most durable.
To be classed as gold-filled the gold layer must be at least 1/50th of the total metal
content, by weight.
Advantages
•
Lightweight
•
Tarnish and perspiration resistant
•
Easy to adjust and align
•
Durable
•
Can be easily repaired
GOLD-FILLED
Disadvantages
•
More expensive than gold plated frames
Figure 16.7: Gold filled (rolled gold) frame material
Gold plated frames are produced first in the base metal, again usually a nickel based
alloy. They are then plated in gold using electroplating (Figure 16.8). Many manufacturers
plate the frame with an impervious layer before gold plating to prevent corrosive
perspiration penetrating through the gold to the base metal.
Advantages
•
Easy to adjust and align
•
Durable
•
Can be easily repaired
•
Cheaper to produce than gold filled frames
Disadvantages
•
More susceptible to corrosion than gold filled frames
GOLD-PLATED
Figure 16.8: Gold plated frame material
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Frame Types and Materials
COMMON FRAME MATERIALS – METAL (cont.)
White gold frames are produced by creating an alloy of gold and other metals, usually
nickel, to give a silver appearance (Figure 16.9).
White gold frames have the same advantages and disadvantages as yellow gold frames.
WHITE GOLD
Figure 16.9: White gold frame material
Stainless steel is more expensive to produce than gold plated frames, however, it is a
useful material for patients who are allergic to nickel (Figure 16.10).
Advantages
•
Hypoallergenic (useful for people with a nickel allergy)
•
Tarnish and perspiration resistant
•
Easy to adjust and align
•
Durable
Disadvantages
•
More expensive than gold plated frames
•
Cannot be repaired
•
Relatively heavy
STAINLESS STEEL
Figure 16.10: Stainless steel frame material
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Frame Types and Materials
COMMON FRAME MATERIALS – METAL (cont.)
Titanium is the most expensive spectacle frame material (Figure 16.11). It is a very light
material and will not corrode. It is, therefore, a very durable material and will outlast other
metal frames. It also holds its adjustment well. Unlike gold frames, however, titanium
frames cannot be soldered with ordinary soldering equipment.
Recent developments included titanium alloys. These materials are known as alphatitanium and beta-titanium. They have most of the advantages and disadvantages of
titanium, listed below, but provide greater flexibility.
Advantages
•
Hypoallergenic (useful for people with a nickel allergy)
•
Tarnish and perspiration resistant
•
Easy to adjust and align
•
Very durable
•
Holds its adjustment well
TITANIUM
Disadvantages
•
Most expensive metal frame material
•
Cannot be easily repaired
Figure 16.11: Titanium frame material
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Frame Types and Materials
MANIPULATION OF SPECTACLE FRAMES
MANIPULATION
Spectacle frames need to be manipulated to insert lenses or to adjust the frame to fit the
patient (Figure 16.12). The various materials require different techniques. In this section
we will consider the requirements of the materials; we will consider steps for adjusting
frames later.
PLASTIC
Most plastic frames need to be heated to insert the lenses or to adjust the temples. Care
must be taken though not to overheat the material (with the exception of Optyl). Acetate
and propionate should not be heated beyond about 70°C. Nylon is very difficult to
manipulate and is best heated in hot water (this is the only material that should be heated
in water).
OPTYL
Optyl prefers a lot of heat (greater than 80°C) and the lenses should be edged slightly
larger than the dummy lenses.
POLYAMIDE
Polyamide prefers less heat and the lenses are best fitted cold. As a result the lenses
should be edged to the size of the dummy lenses and “sprung in”.
Metal frames only require heat to adjust the temple ends so as to avoid cracking the
plastic end-pieces.
METAL
Figure 16.12: Manipulations of spectacle frames
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Frame Types and Materials
SUMMARY
The information above gives some guidance for frame choice and the requirements of materials with regard to
handling, lens fitting and adjusting. The following chapter will build on this with details on how to align and repair
frames.
BIBLIOGRAPHY
Jalie M. 2003. Ophthalmic Lenses and Dispensing. Butterworth Heinemann, London.
Jalie M. 1984. Principles of Ophthalmic Lenses, ABDO, London.
Wakefield KG and Bennet AG. 2000. Bennett's Ophthalmic Prescription Work, Butterworth-Heinemann.
Brooks CW and Borish IM. 2006. System of Ophthalmic Dispensing. Butterworth Heinemann.
Brooks CW. 2005. Essentials of Ophthalmic Lens Finishing. Butterworth-Heinemann.
Wilson D. 2006. Practical Optical Dispensing 2nd Edition. Open Training and Education Network, Sydney.
Wilson D and Stenersen S. 2002. Practical Optical Workshop. Open Training and Education Network, Sydney.
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Frame Types and Materials
NOTES
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