Eyeglasses | Optical Center SmartBuyGlasses IN

What are prism glasses?

It can be normal to experience double vision after a crazy rollercoaster ride or a few too many drinks, but what if your double vision persists? Let’s uncover what prism glasses are. They just might be the right tool to help with your double vision.

Various health problems can cause double vision that can directly relate to your eyes or even your brain. We’ll cover some of the main causes of double vision and how prism correction works as a temporary solution. 

Why do I need prism correction?

Double vision or diplopia is when you see two images of the same object overlap and is the most common visual impairment that prism glasses help correct. Through prism correction, the double images are merged into 1 clear image. 



Essentially double vision is caused by movement problems in your eyes. The muscles and nerves that help your eyes work and move together are complex and originate in the brain. 

When these nerves and muscles are affected or damaged it can cause diplopia. Neurological issues can cause double vision if you’ve, for example, experienced a head injury, brain tumor, or stroke. Another cause can also be strabismus, known also as eye turn which causes one eye to move outward or inward.    



There are other reasons why you may be advised to use prism correction and these symptoms are related to your vision:


• Headaches 

• Eye strain and fatigue

• Difficulty and tiredness when focusing on close up objects 


What is prism correction?

Prism correction is used in eyeglasses to help with diplopia. Prism lenses essentially help double vision through particular lenses that can be infused with glasses that correct farsightedness or nearsightedness. The double image you experience is merged into 1 through the prism correction in your glasses. 

Prism correction does not, however, help with refractive errors as it does not have focusing power. 

How do prism glasses work?

Prisms are glass or transparent objects in a triangular shape with refracting surfaces, imagine a small pyramid made of glass. 


Prism glasses have lenses that are made of prisms that help bend light, before it hits the retina, to illude the eye that an object is in a different position. With farsightedness or nearsightedness, the light enters the retina hitting the same place but not the exact spot. When the light isn’t in the exact same spot, images are less clear. 

When light enters the eye but doesn’t hit the same area, in the retina, you’ll experience double vision. By using prism glasses you can improve your eyes’ alignment and perceive images clearly. Prism correction allows the light to be refracted before entering the retina and focusing light in the same area.  

With prism glasses, you’ll be able to focus both eyes on an object allowing for a single image to appear. Your vision will be the same as any other binocular vision. 


Who can benefit from prism correction?

If you suffer from diplopia (double vision), prism correction is the main solution an eye doctor can prescribe. As we’ve seen, there are various reasons why double vision can present itself and cause discomfort. 

Two main types of double vision are monocular and binocular diplopia. 

Monocular diplopia causes double vision even with one eye closed. Monocular diplopia can be caused by eye health issues such as cataracts or other reasons such as genetics.



Binocular diplopia produces the double vision effect when both eyes are open and disappears if you cover one eye. This type of diplopia has more serious causes and is tied to diverse non-eye-related issues. An example of what can cause binocular diplopia can be neurological problems like multiple sclerosis or can be the consequence of a stroke, or aneurysm. Strabismus can also be identified with binocular diplopia and happens when there is a misalignment with your vision.  

If you suffer from visual or neurological problems that affect your vision and cause you to see double then you should consult an eye doctor.

How to read my prescription with prism glasses

Whether you require distance or progressive lenses, your prescription glasses can be fitted with prism lenses to help correct your double vision.

If you need prism lenses your prescription can start to look a little confusing with all those numbers. We are here to help you read your prescription with prism glasses.



Above you will see a sample prescription that has power values to help correct near distance in both the left and right eye. Your far distance will be indicated by the - underneath spherical (SPH). The cylindrical (CYL) and axis values will only be indicated if you suffer from astigmatism. The last power value (ADD) indicates the need for progressive or bifocal lenses.

In between the axis and ADD value, we have our prism specifications. There are 3 main factors to highlight when you read your prescription with prism lenses:


1. With SmartBuyGlasses, depending on the frame and prescription, the first value will be indicated by a number between 0.5 and 5.0  This refers to the amount of prism correction needed. Some specialized labs can also produce prescriptions above 5.0.

2. This number is then followed by B (base). The base is the part of the lens that will be thicker and indicate the direction of the prism. There is BO (base out), BI (base in), BD (base down), and BU (base up). 

3. BO and BI are known as prism horizontal while BU and BD as prism vertical.



In addition to these values don’t forget to input the correct PD which indicates your pupillary distance. PD is important to calculate correctly as an incorrect value can cause visual discomfort. You can get the correct measurement at your local optician or calculate it yourself with these easy steps in measuring your PD.

How to order prism glasses online

Let’s take our sample prescription from the section above and see how to order prism glasses online with SmartBuyGlasses

Firstly, pick the eyeglasses that most suit you and your style from our wide range of prescription glasses available for women, men, and children. Then choose the distance you need to correct. 

If you then choose to input your prescription manually, here’s how you do it:



1. Your distance correction will go under SPH, for the left and right eye

2. If you suffer from astigmatism, input your values under CYL and axis

3. Don’t forget the correct PD

4. Fill out the values for your prism correction below


If you have any doubts as to how to read and fill out your prescription online ask our in-house opticians.



If you are suffering from double vision (diplopia), due to visual or neurological conditions, then your eye doctor may prescribe prism correction.

Prism correction in your glasses will allow for you to see 1 clear image instead of 2 overlapping images. Great right?!

So, jump on that crazy roller coaster ride with SmartBuyGlasses, get yourself a pair of prism glasses, and enjoy seeing the world in its true single form.

Find high-quality and affordable glasses online, just click here and your double vision is soon a distant memory.