What does it mean to see double images where there should be only one? These double images could appear side by side, on top of one another, or both. Imagine reading a book where the words appear double or imagine driving with such a condition. This is no ghost story but a serious visual impairment that affects your daily activities–a condition known as diplopia, affecting a significant number of the Canadian population.
In this article, we discuss everything you need to know about diplopia from the point of view of Toronto optometrists and the steps you should take to restore your vision if you experience it.
What Is Diplopia?
Diplopia is the perception of 2 images of a single object. This condition can affect one eye (monocular diplopia) or both eyes (binocular diplopia). In cases where it affects both eyes, closing one eye stops the double vision. Diplopia could be a condition itself or an underlying condition.
Symptoms of Diplopia
Diplopia can occur separately or combined with other symptoms. When experiencing double vision, it’s possible to also experience:
- Loss of balance
- Dizziness
- Nausea
- Migraine
- Headache
- Eye misalignment (strabismus)
- Eye weakness
Causes of Diplopia
Temporary episodes of double vision can happen for many reasons, including drinking too much alcohol or being overly tired. This type of short-term double vision is usually not a cause for worry. But if diplopia is long-lasting or keeps coming back, causes can include:
1. Eye Muscle Disorders
When your eye muscles do not align properly, it can lead to double vision. A common eye muscle disorder is strabismus. The misalignment of the eyes often leads to one eye focusing differently from the other causing overlapping images.
2. Nerve Damage or Disorders
Conditions like diabetes or multiple sclerosis that cause nerve issues sometimes disrupt the communication between the brain and the eye muscles. This disruption leads to cranial nerve palsy, which is a common cause of eye misalignment
3. Brain Injuries and Strokes
Traumatic brain injuries and strokes can disrupt the brain’s ability to process visual information accurately. These injuries may impair visual pathways or damage specific brain regions that coordinate eye movements, resulting in diplopia.
4. Lens and Corneal Abnormalities
Structural changes, such as cataracts or irregularities in the cornea, can cause light to refract abnormally, leading to double vision. Conditions like keratoconus, where the cornea thins and bulges, can also distort visual clarity.
5. Systemic Illnesses and Autoimmune Conditions
Graves’ disease, a thyroid-related disorder, often affects eye muscles and leads to diplopia. Autoimmune conditions like myasthenia gravis can also weaken eye muscles, disrupting eye alignment and causing double vision.
What Are Prism Lenses?
Prism lenses made for glasses will appear with one side on either the vertical or horizontal plane thinner than normal, and the opposite side thicker than normal, creating the impression of that typical triangle shape.
By adjusting the angle at which the thinner and thicker sides are, prism lenses can bend all light passing through them in different directions: upwards (superior), downwards (inferior), in towards the nose (nasally), or out towards your ears (temporally). Light can also be bent towards the diagonal directions, although this is less commonly required.
When noted on a prescription, prism is indicated with a power in diopters, much like in the power (SPH) or cylinder (CLY) columns, although it will lack a “+” or “-” indicator. The direction of the base (that thicker side of the lens) would be indicated after the numerical strength of the prism.
For example, a right eye prescription with “2D BO” means the right eye requires 2 diopters of base-out prism.
Prism can be required in just one eye, or both eyes, and can be made with a single vision prescription or a multifocal prescription, similar to how progressive lenses are designed to provide seamless vision at multiple distances. By tailoring the lens to the individual’s specific visual needs, both prism and progressive lenses offer solutions that go beyond standard prescriptions, helping the eyes work comfortably and efficiently throughout the day.
But how do prism lenses help with diplopia?
When light passes through optical prisms, light is bent towards the base, which has the equal effect of shifting the “image” towards the thinner part of the lens, also known as the apex. This has the effect of making it appear as if an object you are looking at is in a different place.
So when used to treat diplopia, prism lenses will shift the image as seen by the affected eye enough so that the brain can merge the images from both eyes together, restoring proper clarity of vision.
What Are Fresnel Prisms?
Another condition that can cause diplopia is physical trauma to the head or upper body. Injuries such as concussions can have a large and lasting impact on the brain, and given how our sight is a result of our brain interpreting signals and images received by the eyes, it is no surprise that a concussion can impact how well we can see.
Whether it is a new difficulty in controlling the muscles that control the movements of the eyes, or if it is confusion in merging those two aforementioned images, trauma-induced diplopia requires correction just as refractive diplopia does.
Diplopia caused by trauma is not typically permanent, but doctors can find it difficult to predict when the symptoms will resolve themselves as the brain heals. To this end, temporary prisms are utilised, as the prescription or power requirement might fluctuate greatly in a short amount of time, and it would be too costly for the patient to purchase new prescription lenses for each change.
A Fresnel prism is a plastic sheet designed to stick to the patient’s lenses, with ridges cut into the surface to induce the refracting prismatic effect. The sheets come premade with different strengths and need only be cut to the shape of the patient’s glasses.
They are attached to the back of the patient’s lenses in the direction required to shift the direction of the image (base up, base down, base in, base out, as mentioned before).
While a Fresnel prism has fewer aesthetic qualities when compared to regular prism lenses, as the lined ridges cut in the plastic are visible if looking at a patient wearing them, they excel as a temporary measure to correct diplopia because they can be removed and interchanged easily should the prismatic power need adjusting or the diplopia resolve altogether.
Conclusion
If you notice persistent double vision, it’s important to act promptly. A professional eye evaluation can determine the underlying cause and guide you to the right treatment, whether it involves prism lenses or other corrective measures. For residents in Toronto seeking reliable care, booking an eye exam near me at our Yorkville or Beaches locations ensures a thorough assessment by our experienced optometrists, giving your vision the attention it deserves.
Frequently Asked Questions
Q: What is double vision a symptom of?
Double vision can result from eye muscle problems, nerve issues, brain injuries, or eye conditions like cataracts. It’s essential to consult a professional to determine the exact cause.
Q: Does double vision go away?
Some cases of double vision are temporary and may resolve on their own, especially if related to fatigue or stress. Persistent double vision usually requires professional treatment.
Q: Can double vision be cured naturally?
Certain exercises and lifestyle adjustments may help with mild double vision, but many cases need medical treatment. It’s best to consult an eye specialist for proper advice.
Q: How to fix double vision at home?
You can try eye exercises and rest breaks to reduce eye strain. However, if double vision persists, seeking professional help is essential for a proper diagnosis and treatment plan.
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