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Prism Lenses for Your Eye Glasses

21 Aug 2012 - Eye Practice
Prism lenses may be prescribed by your optometrist for your eye glasses depending on the eye condition you may have. You may wonder how prisms can work for eye glasses. Here are some important information about prisms you may find useful:

•    They are thin pieces of the optical material used in prescription eye glasses.

•    Their apex is thinner.

•    Their base is thicker. With their light bending properties called index of refraction, the base slows down light that passes through. The base slows down light longer than the apex. Light changes direction down towards the base when it exits the prism. The amount of change will depend on the index of refraction of the material as against the index of refraction of air.

•    The higher index of refraction allows the production of ultra thin lenses that improve appearance and comfort of eye glasses.

•    Normally, lenses with consistent thickness cannot change the direction of the light although they can still slow down the light.


Now, you may ask when eye glasses with prism lenses can be prescribed. Here are some instances when your doctor may require you to wear them:

Crossed Eyes

•    This condition may be referred to as a turned eye or a strabismus.

•    When you have this condition, your eyes can turn in (esotropic) or out (exotropic). They may also turn up or turn down. The eyes may even turn vertically and laterally at the same time.

•    This may result in double vision which can affect your lifestyle and mobility.

•    When you are born with this condition, you may not have double vision because the brain can shut off the part of your vision that perceives double.

•    Prism lenses in eye glasses can address this condition. The lenses will not appear as triangular. They will appear as thicker and thinner edges on the lenses. They may be ground into the shape of the lens or repositioned in the optical center to induce prism. The prism may be adjusted to add prescription as the brain also adjusts to how the eye sees single again.

•    When you suffer from certain medical conditions like diabetes and stroke and they result to double vision, your vision may fluctuate. Thus, the prescription of your glasses needs to be changed frequently to adjust the amount of prism.

•    Fresnel lenses or temporary press on prisms may be used when change is expected but optical quality tends to be poor.


•    This condition refers to the tendency of the eye to turn although it instinctively keeps compensating back.

•    This results in headaches, fatigue while reading and eye strain.

Traumatic Head Injuries

•    When you suffer from these injuries, your optometrist may prescribe yoked prisms to retrain your disrupted visual system by altering spatial perception.

Double Vision

•    This condition may be due to different causes.

•    When you begin to exhibit this symptom, you should see your optometrist immediately so he can check your eyes. He may prescribe eye glasses with prism lenses to address your problem.

•    In some instances, however, you may have a serious medical condition such as diabetes, brain tumor, high-blood pressure and thyroid problems.

Prescribing prism to correct eye muscle imbalances needs to be done accurately. At The Eye Practice complex eye-glass prescriptions is what we do best.  Call us on (02) 9290 1899 or BOOK an APPOINTMENT ONLINE by CLICKING HERE.

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