Details about Terms Used in a Lens Workshop

Terms Used in a Lens Workshop

1. Lens Materials

Glass Lenses – Made from crown or flint glass; scratch-resistant but heavy.
Plastic Lenses – Made from CR-39 (Columbia Resin 39); lightweight and impact-resistant.
Polycarbonate Lenses – Thinner, lighter, and highly impact-resistant; preferred for children and sports eyewear.
High-Index Lenses – Thinner and lighter than standard plastic lenses, used for high prescriptions.

2. Lens Coatings

Anti-Reflective (AR) Coating – Reduces glare and reflections, improves vision clarity.
Scratch-Resistant Coating – Protects against minor scratches and extends lens life.
UV Protection Coating – Blocks harmful ultraviolet rays, reducing the risk of cataracts.
Blue Light Blocking Coating – Reduces digital eye strain by filtering blue light from screens.
Photochromic Lenses (Transitions) – Lenses that darken in sunlight and become clear indoors.

3. Lens Types

Single Vision Lenses – Corrects vision for one distance (near, intermediate, or far).
Bifocal Lenses – Has two focal points: upper part for distance, lower part for near.
Trifocal Lenses – Three sections: distance (top), intermediate (middle), and near (bottom).
Progressive Lenses – Provides a smooth transition between distance, intermediate, and near vision without visible lines.

4. Lens Power Terminology

Diopter (D) – The unit of measurement for lens power.
Spherical Power (SPH) – Corrects myopia (-) or hyperopia (+).
Cylindrical Power (CYL) – Corrects astigmatism; can be negative or positive.
Axis – The orientation of astigmatism correction (0° to 180°).
Add Power (ADD) – Additional power for near vision in bifocal/progressive lenses.

5. Lens Edging and Fitting

Decentration – Adjusting the optical center of a lens to align with the patient’s PD (pupillary distance).
Prism Grinding – Incorporating prism correction in a lens to align images properly.
Beveling – Shaping the edge of the lens for better frame fitting.
Grooving – Creating a groove around the lens to fit into rimless frames.
Polishing – Smoothing the edges of a lens for cosmetic appeal and comfort.

6. Frame and Lens Alignment Terms

Pantoscopic Tilt – The forward tilt of the frame for better vision and comfort.
Retroscopic Tilt – Backward tilt of the frame, rarely used.
Vertex Distance – Distance between the back surface of the lens and the cornea.
Base Curve – The curvature of the front surface of the lens, affecting lens thickness.
Pupillary Distance (PD) – The distance between the centers of the pupils, crucial for proper lens alignment.

7. Optical Aberrations in Lenses

Spherical Aberration – Blurring caused by peripheral rays focusing at different points.
Chromatic Aberration – Color distortion due to different wavelengths bending unequally.
Coma – Off-axis light rays creating a comet-shaped blur.
Astigmatism – Distortion due to unequal refraction along different meridians.

8. Lens Safety Standards

ANSI Z87.1 – Safety standard for impact-resistant lenses.
FDA Drop Ball Test – A test to check lens impact resistance.
ISO Standards – International lens manufacturing and safety guidelines.

9. Lens Manufacturing Techniques

Surfacing – The process of shaping a lens to the required prescription using grinding and polishing.
Casting – Pouring liquid monomer into a mold to create plastic lenses.
Injection Molding – A technique used for polycarbonate lenses, where melted plastic is injected into a mold.
Freeform Technology – Advanced digital lens surfacing that enhances clarity by optimizing every point on the lens.

10. Lens Measurements and Adjustments

Optical Center (OC) – The point on the lens where light passes without deviation; should align with the pupil.
Segment Height – The vertical measurement from the bottom of the frame to the top of the bifocal or progressive segment.
Inset – The inward shift of the near portion of a bifocal/progressive lens to align with the convergence of the eyes.
Prism Thinning – Reducing thickness in progressive lenses by adding a small amount of prism.
Effective Power – The actual power of a lens at a different vertex distance than originally prescribed.

11. Lens Tinting and Special Treatments

Solid Tint – A uniform color applied throughout the lens for cosmetic or sun protection purposes.
Gradient Tint – Darker at the top, gradually fading toward the bottom.
Polarized Lenses – Reduces glare from horizontal surfaces like water, roads, and snow.
Mirror Coating – A reflective coating that reduces light transmission and enhances aesthetics.
Anti-Fog Coating – Prevents condensation and fogging, useful for people wearing masks or working in humid environments.

12. Types of Lens Designs

Aspheric Lenses – Flatter, thinner lenses that reduce peripheral distortions.
Atoric Lenses – Corrects higher levels of astigmatism more precisely than traditional toric lenses.
Double D Bifocal – Has reading segments on both the top and bottom of the lens, useful for mechanics and pilots.
Office/Computer Lenses – Designed for intermediate and near work, reducing digital eye strain.
Lenticular Lenses – Used in very high-power prescriptions to reduce lens weight and thickness.

13. Frame and Mounting Types

Full-Rim Frames – The lens is completely enclosed in the frame.
Semi-Rimless Frames – The lens is held by a frame on the top with a nylon string on the bottom.
Rimless Frames – The lenses are attached directly to the temples and bridge using screws or compression fittings.
Spring Hinges – Hinges that allow temples to flex outward, increasing comfort and durability.
Nose Pads – Adjustable supports that help fit the frame comfortably on the nose.

14. Lens Defects and Quality Control

Power Tolerance – The acceptable range of deviation in lens power.
Wavefront Error – Small distortions in a lens affecting vision clarity.
Warpage – Unwanted curvature in a lens that can cause visual distortion.
Lens Striae – Internal streaks in a lens, usually in glass lenses.
Coating Delamination – When an applied coating (like AR or scratch-resistant) peels off.

15. Specialized Optical Terms

Anisometropia – A condition where the two eyes have significantly different refractive powers.
Aniseikonia – A difference in image size perceived by each eye due to unequal lens magnification.
Prism Diopter (Δ) – The unit of measurement for prism correction, indicating how much light is deviated.
Base Direction – The orientation of a prism (Base Up, Down, In, or Out) to correct diplopia (double vision).

16. Lens Processing Equipment

Lensometer (Focimeter) – A device used to measure lens power and verify prescriptions.
Edger – A machine that shapes lenses to fit into a specific frame.
Groover – Used to cut a groove into the lens for semi-rimless frame mounting.
Tinting Unit – Heats dye solutions to apply color to plastic lenses.
Drilling Machine – Used for rimless frame lens mounting.

17. Frame Adjustments and Repairs

Temple Adjustment – Bending the temple arms to ensure a comfortable and secure fit.
Bridge Adjustment – Modifying the bridge area to prevent slipping or discomfort.
Screw Replacement – Fixing loose or missing screws in the hinges of a frame.
Heat Adjustment – Using hot air or water to soften plastic frames for reshaping.
Pad Arm Adjustment – Changing the position of nose pads for better fit and comfort.

18. Optical Dispensing Terminology

Fitting Cross – A marking on progressive lenses indicating the correct fitting position.
Drop Ball Test – A safety test where a steel ball is dropped onto a lens to check impact resistance.
Segment Width – The horizontal width of the bifocal or trifocal reading area.
Minimum Blank Size (MBS) – The smallest lens blank that can be used to fit a given frame size.
Occupational Lenses – Specially designed lenses for professions requiring specific vision corrections.

Other optical terms

1. Lens Blank

A raw, uncut lens before it is edged and shaped to fit into a frame.
Comes in different diameters and materials.
Has a specific base curve and is processed to match the prescription.

2. Lens Diameter

The size of the lens blank, measured in millimeters (mm).
Standard diameters range from 60 mm to 80 mm, depending on the prescription and frame size.
A larger diameter is used for high prescriptions to ensure proper centration.

3. Effective Diameter (ED)

The largest diagonal measurement of a lens blank that ensures complete frame coverage.
Helps in choosing the correct lens size to avoid thinning at the edges or unwanted thickness.

4. Refractive Index (RI)

A measure of how much light bends (refracts) when passing through a lens material.
Higher refractive index = thinner lenses.
Common refractive indices:
- 1.50 (CR-39) – Standard plastic lenses.
- 1.56, 1.59 (Polycarbonate) – Thinner and impact-resistant.
- 1.67, 1.74 – Ultra-thin lenses for high prescriptions.

5. Abbe Number (V-Value)

A measure of chromatic aberration (color distortion) in a lens material.
Lower Abbe number = more chromatic aberration (more color fringing).
Higher Abbe number = clearer vision with less distortion.
Abbe values of common lens materials:
- Crown Glass – 58 (high clarity).
- CR-39 Plastic – 58 (good clarity).
- Polycarbonate – 30 (low clarity, more aberrations).

6. Crown Glass

Most common type of optical glass, made of silica, soda, and lime.
High clarity, scratch-resistant, but heavier than plastic.
Refractive Index ~ 1.523, Abbe number ~ 58.

7. Flint Glass

Glass with high refractive index due to added lead oxide.
Used in specialized optical applications, not common for regular eyeglasses.

8. CR-39 (Columbia Resin 39)

A lightweight plastic lens material with high optical clarity.
Refractive Index = 1.50 (thicker than polycarbonate).
Abbe Number = 58 (low chromatic aberration, clear vision).
More impact-resistant than glass but less than polycarbonate.

9. Spherical Power (SPH)

The main power of a lens that corrects myopia (-) or hyperopia (+).
Measured in diopters (D).
A -2.00 D lens corrects 2 diopters of myopia.

10. Cylindrical Power (CYL)

Used for astigmatism correction.
Measured in diopters (D), can be negative or positive.
A -1.00 D CYL lens corrects astigmatism along a specific axis.

11. Axis

The orientation of astigmatism correction, measured from 0° to 180°.
Determines where the cylinder power is applied.
Example: CYL -1.00 at Axis 90° corrects astigmatism along the vertical meridian.

12. Meridian

Refers to different angles around the lens, like a clock face.
Principal meridians are the strongest and weakest refractive powers in astigmatic correction.

13. Optical Cross

A graphical representation of lens power in different meridians.
Used to visualize spherical and cylindrical corrections.
Helps in understanding how astigmatism correction works.

14. Near Add (Addition Power)

The additional power needed for near vision in bifocal or progressive lenses.
Measured in diopters (D).
Example: If a patient’s distance power is -2.00 D and the near add is +2.50 D, the reading prescription is +0.50 D.

15. Prism

Used to correct eye misalignment (diplopia, strabismus, or phorias).
Measured in prism diopters (Δ).
Base Direction:
- Base In (for divergence correction).
- Base Out (for convergence correction).
- Base Up / Down (for vertical misalignment).

16. Decentration

The process of moving the optical center of a lens to match the patient's pupillary distance (PD).
Ensures proper visual alignment and avoids unwanted prismatic effects.
Formula: $\text{Decentration} = \frac{\text{Frame PD} - \text{Patient's PD}}{2}$

17. Base Curve (BC)

The front surface curvature of a lens.
Affects lens thickness and optical performance.
Example:
- Low Base Curve (Flat Lenses) – Thinner, better aesthetics.
- High Base Curve (Curved Lenses) – Used in wraparound sports frames.

18. Cross Curve

The steeper curvature of a toric lens used for astigmatism correction.
Found on the front surface of the lens.

19. Ocular Curve

The back surface curve of a lens.
Affects the fit and comfort of the lens.

20. Surface Power

The power of a single surface (front or back) of the lens.
Calculated using the Lensmaker’s Equation: $F = \frac{(n-1)}{r}$ where F is power, n is refractive index, and r is radius of curvature.

21. Surface Curvature

The degree of curvature on a lens surface, affecting optical performance.
Measured in diopters (D).

22. Corridor Length

Found in progressive lenses (PALs).
The distance between the fitting cross and the near reading zone.
Shorter corridors are used for small frames, while longer ones provide a wider intermediate zone.

23. Free-Form Technology

Advanced digital lens surfacing for precise vision correction.
Uses computer-controlled surfacing to customize the lens for each patient.
Provides wider, distortion-free vision zones in progressive and single-vision lenses.

24. Lacquer

A protective coating applied to lenses for scratch resistance.
Used in hard coatings and anti-reflective (AR) coatings.

25. Etching

A process of marking identification numbers or logos on lenses.
Used for progressive lens markings to identify the corridor length and brand.

26. Generator

A machine used in lens surfacing to cut and shape lenses into the correct prescription.
Removes excess material from the lens blank before polishing.

27. Lens Surfacing

The process of grinding and shaping a lens to achieve the correct prescription.
Involves blocking, generating, smoothing, and polishing.

28. Lens Polishing

A step in surfacing where a polishing compound is applied to smooth out lens surfaces.
Ensures a clear, distortion-free surface before coatings are applied.

29. Lens Grooving

A process of cutting a groove along the lens edge for semi-rimless frames.
Done using a groover machine or hand tools.

30. Chiller

A cooling system used in lens processing machines.
Prevents overheating of lenses during grinding and edging.

31. Varnish

A protective layer applied to lenses after polishing.
Used to enhance scratch resistance and durability.

32. Edging

The process of cutting lenses to fit into frames.
Done using an edger machine that shapes the lens according to the frame size.

33. Glazing

The final step of lens fitting where the cut lens is mounted into the frame.
Includes adjusting the bevel, size, and alignment for a secure fit.

34. Bevel

The angled edge of a lens that helps it fit into the groove of a full-rim frame.
Common types:
- Standard Bevel – For regular full-rim frames.
- Step Bevel – For sports and wraparound frames.
- Flat Bevel – For specialty lenses.

35. Emery

A fine-grain abrasive material used for lens polishing.
Helps remove scratches, imperfections, and fine roughness.

36. Abrasives

Materials used in grinding, surfacing, and polishing lenses.
Examples:
- Aluminum oxide – Used for rough grinding.
- Cerium oxide – Used for fine polishing.

37. Chuck

A clamping tool that holds the lens securely during edging and surfacing.
Prevents lens slippage and misalignment.

38. Newton's Ring

A circular interference pattern seen when a curved lens surface contacts a flat surface.
Used to check lens surface quality and uniformity.

39. Test Plate

A standard reference lens used for checking the accuracy of surfaced lenses.
Helps detect errors in curvature and power.

40. Button

The center portion of a lens blank before it is shaped into a prescription lens.
Found in glass lens manufacturing before surfacing begins.

41. Depression Curve

The concave curvature found in some high-power lenses.
Used to reduce lens thickness and improve cosmetics.

42. Cribbing

The process of removing excess material from the lens blank before edging.
Prevents unnecessary weight and thickness.

43. Shanking

The process of trimming the lens edge to improve the fit inside a frame.
Helps adjust bevel size and position.

44. Trepanning Tool

A specialized cutting tool used for making precise holes in rimless lenses.
Ensures clean, accurate drill holes for mounting rimless frames.

45. Lens Form

The shape and curvature of a lens surface, affecting vision and thickness.
Common forms include:
- Meniscus Lens – One convex and one concave surface.
- Biconvex/Biconcave – Both surfaces either convex or concave.
- Plano-Convex/Plano-Concave – One flat, one curved surface.

46. Lens Marking

Used in progressive and multifocal lenses for alignment and verification.
Includes logos, alignment dots, and reference points for lens positioning.

47. Transverse Test

A test used to check the thickness and uniformity of a lens.
Ensures the lens meets safety and durability standards.

48. Vertex (Vertex Distance)

The distance between the back surface of the lens and the cornea.
Important for high-power lenses, as small changes affect prescription accuracy.

48. C-Sizer

A tool used to measure the circumference of a lens for correct edging.
Ensures a precise fit into frames.

49. Caliper

A precision measuring tool for lens thickness and diameter.
Helps verify lens dimensions before mounting.

50. Colmascope

A device used to check lens stress patterns in glass and plastic lenses.
Detects internal stress caused by manufacturing or fitting errors.

51. Crazing

Fine cracks appearing on lens coatings (AR or hard coat).
Caused by heat exposure, age, or improper cleaning methods.

52. Edger Vomit

Residue (dust, liquid, and lens particles) generated during lens edging.
Needs proper cleaning and disposal in lens workshops.

53. Equithin

A technique used in progressive lenses to balance thickness.
Ensures thinner, lightweight lenses, especially for high prescriptions.

54. Groover

A machine used to cut a groove along the lens edge for semi-rimless frames.
Ensures proper fit into frame wire.

55. Hide-a-Bevel

A beveling technique where the edge of the lens is angled to reduce visibility.
Used in high-powered lenses to improve aesthetics.

56. Hydrophobic Coating

A special coating that repels water, oil, and dirt.
Found on anti-reflective (AR) lenses for easy cleaning and durability.

57. Image Jump

A sudden shift in image position caused by a bifocal segment.
More noticeable in high-powered bifocal lenses.

58. Impact Resistance

The ability of a lens to withstand force without breaking.
Polycarbonate and Trivex lenses are the most impact-resistant.

59. Segment Inset

The horizontal shift of the near segment in bifocal lenses toward the nose.
Compensates for the natural inward movement of the eyes when reading.

60. Laminated Lens

A lens made of multiple layers for added strength and coatings.
Used in polarized and high-index lenses.

61. Lap

A tool used in lens polishing to shape the lens surface.
Different laps are used for different curvatures.

62. Lens Clock (Sag Gauge)

Measures the curvature of a lens surface.
Helps determine base curve and power.

63. Lens Washer

A machine that cleans lenses after processing.
Removes debris, polishing residue, and coatings.

64. Safety Bevel

A rounded edge on a lens to prevent sharp edges.
Increases comfort and safety, especially for rimless frames.

65. Swarf

Fine lens shavings and dust created during grinding and edging.
Proper removal is needed to keep the workshop clean and equipment functional.