6.1 Frame Materials

6.1 Frame Materials

Introduction to Ophthalmic Frame Materials

In modern ophthalmic dispensing, the selection of the spectacle frame material is a critical decision that influences a patient's visual comfort, physical safety, skin health, and the longevity of the eyewear. An optician must be an expert in the properties of both plastic (polymer) and metal (alloy) materials. Each material behaves differently when subjected to stress, heat, adjustments, and the chemical environment of the wearer's skin.

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Plastic Frame Materials

Plastic frames, historically referred to as shell or horn frames, are popular for their aesthetic variety, rich color patterns, and ability to hold thick lenses. However, they vary significantly in their reaction to heat, tensile strength, and chemical durability.

Cellulose Acetate (Zyl)

Cellulose acetate, commonly known in the optical industry as zyl, is the most widely used plastic frame material. It is a plant-based plastic derived from cotton linters and wood pulp, processed with plasticizers to improve flexibility.

• Manufacturing Process: Zyl frames are typically cut from flat sheets of laminated plastic, which allows for complex, multi-layered color patterns.
• Physical Properties: Zyl is relatively lightweight, accepts a high polish, and is available in almost limitless colors.
• Adjustment and Heat Sensitivity: Zyl is highly thermoplastic. When heated using a hot air frame warmer or a salt pan to approximately 120°F to 140°F (49°C to 60°C), it becomes soft and pliable, allowing the optician to adjust the temple bends, endpieces, and bridge. Once adjusted, it must be cooled in water to set its shape.
• Limitations: Zyl is susceptible to aging. Exposure to ultraviolet (UV) light, sweat, and facial oils causes the plasticizers to leach out over time. This leads to a dry, brittle frame that exhibits a whitish residue known as oxidation or blooming. Zyl can also warp or lose its shape if left in high-heat environments, such as on a vehicle dashboard in the summer.

Cellulose Propionate

Cellulose propionate is an injection-molded plastic chemically similar to acetate but formulated with propionic acid.

• Physical Properties: Propionate is lighter, thinner, and has a harder surface than zyl. Because it is injection-molded, it is typically cheaper to manufacture.
• Adjustment: It requires less heat to adjust than zyl, but it is highly heat-sensitive. Overheating propionate will cause it to shrink, bubble, or stretch uncontrollably. An optician must use caution and lower heat settings when adjusting this material.
• Hypoallergenic Nature: Unlike zyl, propionate is generally considered hypoallergenic because it contains fewer skin-sensitizing plasticizers.

Nylon, Polyamide, and Grilamid

Nylon-based materials, including polyamide and co-polyamides like Grilamid, are highly flexible, lightweight, and durable polymers.

• Physical Properties: Nylon is virtually indestructible. It exhibits high impact resistance and is completely resistant to common solvents, sweat, and environmental exposure.
• Adjustment: Nylon is cold-adjustable or requires minimal heat. Because of its high elastic memory, it resists permanent deformation and will spring back to its molded shape.
• Applications: Nylon is the premier material for sports eyewear, industrial safety goggles, and children's frames. Its main drawback is that it cannot be easily dyed or painted, restricting it to solid, molded colors.

Optyl

Optyl is a patented, epoxy-resin plastic that is thermo-elastic and completely hypoallergenic.

• Thermo-Elastic Memory: Optyl features a unique chemical structure that has shape memory. When heated to its activation temperature of 180°F to 200°F (82°C to 93°C), it becomes extremely soft, resembling rubber. The optician can stretch or bend the frame to fit the patient's face. Once cooled, it holds this shape perfectly. However, if the frame is reheated, it will automatically revert to its original factory-molded shape.
• Advantages: Optyl is 30% lighter than zyl, does not contain plasticizers (making it 100% hypoallergenic), and does not oxidize or lose its finish when exposed to skin acids.
• Limitations: It cannot be adjusted cold; attempting to bend Optyl without adequate heat will cause it to snap cleanly.

Carbon Fiber

Carbon fiber frames utilize carbon strands embedded in a resin matrix.

• Physical Properties: This material is exceptionally strong, thin, and lightweight. It does not stretch, warp, or degrade.
• Adjustment: Carbon fiber cannot be adjusted with heat or cold. To overcome this limitation, manufacturers typically insert metal cores into the temples so the optician can bend the temple tips to fit the patient.

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Metal Frame Materials

Metal frames offer a classic, low-profile design. Their selection is often governed by weight, mechanical strength, and potential skin allergies.

Monel

Monel is a nickel-copper alloy containing roughly 60-70% nickel, along with copper, iron, and manganese.

• Physical Properties: Monel is the most common metal frame material due to its high strength, ease of soldering, and excellent adjustability.
• Allergic Reactions: Because of its high nickel content, monel is a frequent trigger for contact dermatitis (nickel allergy). The reaction causes skin redness, itching, and a greenish oxidation mark on the skin where the frame rests.
• Prevention: Monel frames must be plated and coated with a protective lacquer. If this coating wears thin, the nickel will react with the wearer's perspiration and irritate the skin.

Titanium and Beta-Titanium

Titanium is a premium, pure element used in high-end eyewear.

• Physical Properties: Pure titanium is 40% lighter than standard metals, stronger than steel, and highly resistant to corrosion from sweat, acids, and saltwater.
• Hypoallergenic: It is 100% hypoallergenic and is the material of choice for patients with severe metal allergies.
• Beta-Titanium: This is an alloy of titanium combined with metals like aluminum and vanadium. It is more flexible than pure titanium, making it easier for the optician to make fine adjustments while retaining excellent strength and hypoallergenic properties.

Stainless Steel

Stainless steel is an iron-chromium alloy that may contain small percentages of nickel.

• Physical Properties: Stainless steel frames are strong, thin, highly resistant to corrosion, and lightweight.
• Adjustment: It is springy and holds adjustments well. It is relatively hypoallergenic, especially when labeled as nickel-free.

Memory Metals (Flexon)

Memory metal (commonly known as Flexon) is a titanium-nickel alloy (Nitinol).

• Elastic Shape Memory: It can be twisted, bent, or crushed and will immediately snap back to its original shape without damage.
• Adjustment: This elasticity makes Flexon highly durable, but it makes customized fitting adjustments (such as adding pantoscopic tilt or temple wraps) nearly impossible because the metal springs back to its manufactured shape.

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Material Properties Comparison