If you have trouble reading anything for more than a couple of minutes – if you can’t seem to focus, or get headaches while reading, or find that the words jump around in a blur – but you’re totally fine doing other normal daily activities, you might need lenses with prisms. A comprehensive eye exam can detect whether prisms might help you focus on printed words and fine details without suffering unpleasant side effects like headaches and dizziness from doubled vision.

Why might I need prisms?

Sometimes, people who don’t necessarily have an underlying refractive error have eyes that tend to pull apart when they are called upon to focus. While this used to be colloquially known as ‘lazy eye’ or ‘wandering eye’, it is actually a condition wherein one eye wants to be dominant rather than working in concert with the other eye. Whether the submissive eye wanders up, down, to the left or to the right, it’s caused by a muscular imbalance; the dominant eye has become stronger while the other cannot stay focused on the task at hand. This muscular imbalance is known as a fixation disparity.

Where prisms come in to help relieve the symptoms of the imbalance is not so much by focusing the less dominant eye, but by tricking the brain into thinking both eyes are working together. Other than laser eye surgery, which can sometimes correct the need for prisms (but not always), prisms provide the most reliable relief from a fixation disparity. Sometimes the condition can be corrected by wearing contact lenses, but not all people who need prisms are good candidates for contacts.

How do prisms work?

Prisms work in eyeglasses by bending light in order to trick the brain into thinking that both eyes are focused on the same thing. This reduces eyestrain and doubled vision by aligning the two images properly so that people with a fixation disparity see things as they are, rather than as they look to two separately focused eyes. Prisms do the same job in eyeglasses that decorative ones do in windows: bend ordinary while light. In glasses, the prisms bend and bounce light in such a way that it effectively makes the eyes think they are pulling together.

A comprehensive eye exam can detect whether prisms are right for you

Among the many types of ocular and medical tests performed at Toronto Eye Care are tests to determine whether or not your vision is properly aligned. If it’s not, prisms can help bring your vision back into alignment and reduce your discomfort levels when reading and doing close work. In addition to binocular vision testing to determine whether you are seeing blurry or double, you can also expect a full diagnostic workup of tests that include:

• Refractive tests to determine degree of nearsightedness/farsightedness
• Corneal curvature and thickness tests to determine astigmatism and suitability for laser eye surgery
• Retinal scan to detect holes, tears and detachments
• Tests for diseases such as glaucoma and AMD
• Colour vision testing

And, of course, after the eye exam, you will not only receive a current eyeglass/contact lens prescription that can be filled at our convenient onsite dispensary, but also counselling, treatment and referrals to experts if necessary, who can provide a further medical plan of action.

If you’re wondering whether your problems focusing indicate a need for prisms, schedule an eye exam for professional advice.