Anatomy of an Eyeglass Frame
Every eyeglass frame, regardless of material or style, is composed of specific components. Knowing the correct terminology and function of each part is essential for the ABO exam and for communicating with labs, patients, and colleagues. Think of the frame as having two main sections: the frame front and the temples.
The Eyewire (Rim)
The eyewire is the circular or shaped ring that holds the lens in place. In full-rim frames, the eyewire completely surrounds the lens. The eyewire's inner groove accepts the beveled edge of the lens, keeping it securely seated.
Each frame has two eyewires, one for each lens. The eyewire typically has a small screw at one point (the eyewire closure) that allows the eyewire to open slightly for lens insertion. This screw must be kept tight; a loose eyewire screw is the most common cause of a lens falling out.
The Bridge
The bridge connects the two eyewires across the nose. It plays a crucial role in determining how the frame sits on the patient's face. Bridge design affects:
- Vertical position of the lenses relative to the eyes (optical center alignment)
- Weight distribution on the nose
- Comfort during extended wear
- Frame stability
Bridge types include:
- Keyhole bridge: Named for its keyhole shape when viewed from above. Sits higher on the nose and allows the frame to rest on a smaller contact area. Common in vintage and retro styles.
- Saddle bridge: A smooth, continuous curve that distributes weight evenly across the top and sides of the nose. Common in plastic frames and generally the most comfortable design for prolonged wear.
- Pad bridge: Uses separate adjustable nose pads attached to pad arms. Found in metal frames and some plastic frames. Allows for precise positioning of the frame on the nose.
The Endpiece
The endpiece is the portion of the frame front that extends laterally from the outer edge of the eyewire to the hinge point where the temple attaches. Endpieces can be:
- Integral (molded as one piece with the frame front)
- Separate components joined to the eyewire by screws or solder
The endpiece determines the angle at which the temple extends back from the frame. If the endpiece is angled incorrectly, the temples will not follow the contour of the patient's head properly.
Temples
Temples are the arms that extend from the frame front back along the sides of the head to the ears. They are connected to the endpiece by the hinge. Temples serve two purposes: they hold the frame on the head and they position the frame at the correct distance from the face.
Temple length is measured from the hinge to the end of the temple tip. Standard temple lengths range from about 130 mm to 150 mm, with 140 mm being the most common. Proper temple length ensures the bend falls at or just behind the top of the ear.
Temple Tips
Temple tips (also called earpieces or temple covers) are the protective covers at the end of each temple. They serve both comfort and functional purposes:
- Cushion the temple against the skin behind the ear
- Provide grip to prevent slipping
- Protect the skin from direct contact with metal or sharp temple ends
Temple tips may be made of acetate, silicone, rubber, or other soft materials. Silicone tips offer more grip and are useful for patients whose glasses tend to slide.
Nose Pads
Nose pads are small pads that rest directly on the nose, supporting the weight of the frame. They are found on pad-bridge frames (mostly metal frames) and connect to the bridge via pad arms.
Nose pad materials include:
- Silicone: Soft, grippy, hypoallergenic. The most popular choice.
- PVC (polyvinyl chloride): Firm, durable, less expensive. Can cause reactions in sensitive patients.
- Titanium: Lightweight, hypoallergenic, found on premium frames.
- Glass/crystal: Smooth, firm, hypoallergenic. Less common.
Nose pads come in various shapes, including oval, round, D-shaped, and teardrop. The D-pad is among the most common, named for its flat-sided shape that distributes weight along the side of the nose.
The Hinge
The hinge connects the temple to the endpiece, allowing the temple to fold inward for storage. Standard barrel hinges use interlocking barrels (typically 3 or 5) held together by a pin or screw. Variations include:
- Standard barrel hinge: Simple, reliable, but can loosen over time
- Spring hinge: Contains an internal mechanism allowing outward flex beyond the normal open position
- Hingeless: The temple is flexible enough to fold inward without a traditional hinge mechanism
Frame Identification Markings
Frames are marked with key measurements and information, typically printed on the inside of the temple:
- Eye size: The horizontal lens width in millimeters
- Bridge size: The distance between the lenses at the narrowest point of the bridge
- Temple length: Length from hinge to temple tip end
- Brand, model, and color: For reordering and identification
These measurements are written in the format: Eye size □ Bridge size - Temple length (e.g., 52 □ 18 - 140).
Clinical Relevance
Every frame adjustment involves these components. When a patient says their glasses are "not sitting right," you systematically evaluate: Are the pad arms creating proper nose contact? Is the bridge width correct? Are the temples the right length? Is the hinge tight? Component-level understanding transforms troubleshooting from guesswork into a systematic process.
Key Takeaways
- The eyewire holds the lens; its closure screw must be kept tight
- The bridge determines how the frame sits on the nose and distributes weight
- Endpieces connect the eyewires to the temples at the hinge point
- Temple length should place the bend at or just behind the top of the ear
- Nose pad adjustments on pad arms are among the most impactful fitting adjustments
- Frame markings follow the format: eye size □ bridge size - temple length