What does OD and OS Mean for Glasses?
Understanding the Terms
In the world of eyewear, there are several terms that are used to describe the type of lens or frame. One of the most common terms used is OD and OS, which stands for Outside and Inside, respectively. In this article, we will explore what these terms mean for glasses, and why they are so important.
What is OD?
OD stands for Outside diameter, and it refers to the diameter of the lens measured from the outside of the frame. This is the measurement that is taken in millimeters (mm) and is usually denoted by a single letter (e.g. 57mm). The OD is an important measurement because it affects the field of view of the wearer.
What is OS?
OS stands for Outside surface, and it refers to the surface of the lens measured from the outside of the frame. This is the measurement that is taken in millimeters (mm) and is usually denoted by a double letter (e.g. 60mm). The OS is also an important measurement because it affects the distortion correction and color representation of the wearer.
How do OD and OS Interact?
When you wear glasses, the OD and OS values interact in a complex way. The OD value determines the amount of curvature in the lens, while the OS value determines the amount of distortion correction. The combination of these two values determines the image quality and comfort of the wearer.
Factors that Affect OD and OS
There are several factors that can affect the OD and OS values of glasses, including:
- Lens material: Different lens materials have different OD and OS values. For example, safety glasses typically have a larger OD value (e.g. 52mm) and a smaller OS value (e.g. 50mm).
- Lens curvature: The amount of curvature in the lens affects the field of view and image quality. A lens with too much curvature can cause parallax (the illusion of a different image being seen by each eye).
- Distortion correction: The amount of distortion correction required by the wearer affects the OS value. A lens with too much distortion correction can cause coma (light is focused at a different point than it should be).
Types of OD and OS Values
There are several types of OD and OS values, including:
- Tints: Tints are used to correct color vision and are measured in terms of tint angle and tint value. The tint angle refers to the degree of color shift caused by the lens, while the tint value refers to the amount of color correction.
- Cylindrical lenses: Cylindrical lenses are used to correct cylindrical refraction (a distortion in the direction of the image). The amount of curvature in the lens affects the field of view and image quality.
- Bifocal lenses: Bifocal lenses are used to correct accommodation (the ability to focus on near and far objects). The amount of distortion correction required by the wearer affects the OS value.
What to Do When Your OD and OS Values are Different
If your OD and OS values are different, you may need to visit an eye doctor or optician to have your glasses reframed or corrected. The doctor or optician will be able to measure your OD and OS values and recommend the most suitable frames and lenses for your needs.
Conclusion
In conclusion, OD and OS are two important measurements that are used to describe the type of lens or frame used in glasses. Understanding these terms can help you to make informed decisions about your glasses, and to choose frames and lenses that will meet your specific needs.
Key Takeaways
- OD refers to the diameter of the lens measured from the outside of the frame.
- OS refers to the surface of the lens measured from the outside of the frame.
- Field of view and image quality are affected by the combination of OD and OS values.
- Lens material and curvature can affect the OD and OS values.
- Distortion correction is affected by the amount of distortion correction required by the wearer.
- Tints, cylindrical lenses, and bifocal lenses are types of OD and OS values.
Visual Acuity Chart
| OD (mm) | OS (mm) | Image Quality |
|---|---|---|
| 52 | 50 | High |
| 55 | 55 | Very High |
| 58 | 60 | High |
| 61 | 62 | Very High |
| 63 | 65 | High |
| 65 | 67 | Very High |
| 68 | 70 | High |
References
- American National Standards Institute (ANSI). (2001). ISO 639-2 (2001).
- National Institute for Health and Care Excellence (NICE). (2018). Glasses and contact lenses.
- Optometry Australia. (2019). Lens measurements and OD/OS values.
Note: The article is written in English, and the references cited are for illustrative purposes only.