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Some people have small triangular symbols or "prism" on their prescriptions, as well as vertical and horizontal with numbers. So, what are the numbers and directions of these prisms, and what are their uses?

The human eye is a complex organ that plays a crucial role in vision. Sometimes, the eyes can become misaligned, causing double vision, discomfort, and other vision-related issues. This is where a prism can come into play. In this article, we will be discussing what a prism is, how it works, and its benefits when used in prescription lenses.

prism glasses

What is a Prism?

A prism is a triangular shaped piece of glass or plastic that is used to correct certain types of double vision. It works by bending light and changing the direction in which it travels. There are several types of prisms, including triangular prisms, pentagonal prisms, and more.

How does a Prism work?

The primary function of a prism is to correct double vision. This is accomplished by realigning the light that enters the eye. A prism works by bending light, which changes the direction in which it travels. This allows the two eyes to see a single image instead of two separate images.

Prisms are measured in diopters, which is a unit of measurement that indicates the amount of bending power the prism has. This measurement is crucial when adding a prism to a prescription lens. The diopter measurement must be accurate to ensure the prism is effective in correcting double vision.

prism lens

Adding Prism to prescription lenses

When a person is diagnosed with double vision, their doctor may recommend adding a prism to their prescription lenses. This requires a comprehensive assessment to determine the amount of prism that is needed. The prescription lenses are then customized for the individual's needs, taking into account the prism measurement, lens type, and other relevant factors.

Benefits of using Prism in prescription lenses

The primary benefit of using a prism in prescription lenses is improved vision. A prism can effectively correct double vision and alleviate the discomfort associated with it. It can also correct muscle imbalances, which can cause the eyes to turn in different directions. By realigning light and correcting double vision, a prism can help to improve overall visual acuity.


In conclusion, a prism is a triangular shaped piece of glass or plastic that is used to correct certain types of double vision. It works by bending light and changing the direction in which it travels, allowing the two eyes to see a single image. When added to prescription lenses, a prism can significantly improve vision and provide relief from the symptoms associated with double vision. If you are experiencing double vision, it is important to consult with a doctor to determine if a prism is right for you.

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