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What Are Prisms and How Do They Correct Your Double Vision?

What Are Prism Lenses?

Most patients who need eyeglasses to address nearsightedness or farsightedness are prescribed spherical and cylindrical lenses. These provide patients with excellent focus by correcting for refractive errors, so light reaches its destination.

When a patient’s binocular vision — the eyes’ ability to work together to create one clear image — isn’t well developed, a misalignment between the two eyes occurs. This can cause double vision, also known as diplopia.

When the eyes are misaligned, they struggle to work together to create a single image. Instead, they send two images to the brain, one appearing higher, lower, or to the right or left of the other image.

Prism lenses are required when a person has double vision, as the eyes are misaligned and the brain cannot fuse the two images into one single clear image. These lenses correct the misalignment as they move the perceived position of one image.

For example if you see two images and one is higher than the other, the prism lens will move the one image downwards – allowing the brain to fuse the images and removing the double vision.

Prism Lenses to Help Your Vision

Prisms are an integral part of vision therapy, which consists of customized exercises and lenses to improve visual processing by retraining the brain and eyes to work together. Prisms improve patients’ depth perception and spatial perception.

During the therapy sessions, your eye doctor will fit you with prism glasses, provide instruction, and ask what you are seeing and experiencing. These responses will provide them with valuable information on the prisms’ effectiveness.

Below are the types of exercises you may be asked to perform during a vision therapy session to test how well the prism lenses are working.

  • Balance and depth perception – For this, your eye doctor might ask you to walk to a wall or down the office’s corridor, or to hold an object and look at the top of it from an arms-length distance.
  • Peripheral Vision – While walking or holding an object, you may be asked to identify objects on either side while looking straight ahead.
  • Balance/coordination – An exercise could involve looking straight ahead while slowly walking, step by step, toe to heel while maintaining your balance.

Prism lenses and the vision therapy exercises stimulate your brain, gradually developing a stronger eye-brain connection. Your eyes will learn to work together to regain clear and comfortable vision. This, in turn, will lead to improved balance and coordination, even when you are no longer using prisms. If you have been experiencing double vision, imbalance or depth-perception problems, schedule an appointment with Calgary to discuss how vision therapy involving prisms might help.

At Calgary we will gladly answer your questions about the role prism lenses play in vision therapy.

At Browz Eyeware, we put your family’s needs first. Talk to us about how we can help you maintain healthy vision. Call us today: 587-600-0644 or book an appointment online to see one of our Calgary eye doctors.

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How to Read Your EyeGlass Prescription

It is important to understand your prescription, especially if you are traveling and your lenses break or get lost. Knowing what your prescription means also helps you understand your eyes better. Your prescription is not just a series of numbers, but also an important indicator of your eye health. Higher prescriptions increase your risk of developing serious eye conditions later in life.

If you don’t know how to read your prescription, being able to know what lenses are right for you can get complicated.

What Do All These Letters and Numbers Mean?

The numbers on your eyeglass prescription describe precisely how your lenses should be cut. It’s important to keep your prescription up to date so these numbers accurately reflect your visual needs. Typically, on a prescription, you’ll see several abbreviations and words labeling all of the important data on your prescription.

OD vs. OS Eye

Sometimes the letters R (for right eye) and L (for left eye) are used, but on some prescriptions, you may see OD and OS. OD is short for the Latin term oculus dexter, which means right eye. OS is an abbreviation of the Latin oculus sinister, which means left eye. You’ll often see these terms on eyeglass prescriptions.

Sphere, Cylinder, and Axis on Eye Prescriptions

Sphere: The sphere (SPH) on your prescription indicates the base of lens power you need to see clearly. A minus (-) symbol next to this number means you’re nearsighted, and a plus (+) symbol is meant to correct farsightedness.

Cylinder: The cylinder (CYL) number indicates the lens power needed to correct astigmatism —

when the eye isn’t completely round, resulting in distorted or blurred vision. The CYL is a power number indicating the amount of cylinder power to correct the astigmatism. If this column is blank, it means you don’t have astigmatism.

Axis: An axis number will also be included if you have astigmatism. This number indicates the angle of the cylinder power in the lens to correct your astigmatism.

Other Terms You May Find On Your Prescription

A prescription for correcting eye alignment issues will include a PRISM and BASE value. These are needed to design the lens so that it can accurately correct the eyesight in the event of a misalignment between the two eyes. The base value will show either “in” or “out,” or “up” and “down,” indicating the direction the prism should be angled.

Another part of your prescription may include ADD, meaning Addition. It stands for additional correction that you need for reading. It is used when reading, bifocal, or multifocal glasses are needed. It represents an additional power over the distance prescription.

Contact us today to schedule an eye exam and learn more about your eyeglasses prescription.

At Browz Eyeware, we put your family’s needs first. Talk to us about how we can help you maintain healthy vision. Call us today: 587-600-0644 or book an appointment online to see one of our Calgary eye doctors.

Frequently Asked Questions with Dr. George Fung

Q: Can you request lenses made from glass? Is glass still used for lenses?

  • A: Yes. Opticians still sometimes use glass for lenses. However, glass is not used very often because they aren’t as safe. If these glass lenses breaks, they can shatters into many pieces and can injure the eye. Glass lenses are much heavier than plastic lenses, so they can make your eyeglasses less comfortable to wear.

Q: Can a coating be added to eyeglasses to protect them from further scratches?

  • A: A protective coating can’t be added to a lens after it’s scratched. The coating is applied when the lens is manufactured and can’t be put on later.

Quality Frames For Prescription Eyeglasses & Computer Glasses In Calgary, Alberta. Visit Browz Eyeware for an eye exam and eyeglasses that match your style.

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