Tropia vs Phoria: strabismus information

You’re at your local optometry office, sitting in the big chair with all the fun-looking gadgets attached to it. Your optometrist walks in and begins your yearly eye exam. The doctor puts up a letter on the eye chart and begins to wave a black paddle in front of each eye. What is the doctor testing for when doing this?

Healthy eyes are aligned and are able to work together to give you clear and single vision. Since our eyes are situated on different sides of our face, the images each eye sees when viewing objects are slightly different. Even so, the two images that enter the right and left eyes are combined into one clear image by the brain. This is known as binocular vision and it is what gives us a sense of certain elements, like distance and three-dimensionality. There are many cases though where the eyes are not in alignment with each other and the two eyes see not-so-slightly different images. The brain has trouble combining the two views, resulting in double vision.

Strabismus is the term to describe when one’s eyes are misaligned. The degree of misalignment can vary, ranging from small to large angle deviations. It can always be present, which we call “constant,” or can occur some of the time, which we call “intermittent.” The different types of strabismus are as followed:

• Exotropia: Eyes are deviated outwards
• Esotropia: Eyes are turning inwards towards the nose
• Hypertropia: Eyes are deviated upwards
• Hypotropia: Eyes are deviated downwards.

Smaller-angle strabismus (or tropias) are more difficult to diagnose since they aren’t as obvious. This is why the doctor will wave a black paddle in front of each eye. This is known as the cover-uncover test. This test consists of covering one eye and looking at the movement of the other eye. For example, the optometrist covers the right eye and the left eye is steady. This means that the eye is aligned and normal. Now the doctor will uncover the right eye and proceed to cover the left eye. The right eye moves, meaning that it is misaligned. Since the left eye is covered, the patient can only see through the right, so it moves to correct itself to be able to see.

Not all eye misalignment can affect one’s binocular vision. Tropia is a result of trying to use both eyes to see, but the turned eye makes it difficult for the brain to create a clear picture. There are many cases of those who have eye misalignment, but it doesn’t affect their binocular vision. No one has eyes that are completely straight. Everyone’s eyes are angled differently and when they aren’t being used to view objects/distances, they go from straight to its relaxed position. This can then give off a slight turned eye look. However, when the eyes are needed again for binocular vision, the “turned” eye will correct itself and work in sync with the other eye. This is known as heterophoria, or just phoria.

To test for phoria, doctors will do the cross-over test, which is when one eye is covered and then the other eye is quickly covered after. The covering of the eyes back and forth will break the eyes’ synchronization for binocular vision and you can then tease out the phoria. If one of the eyes is steady, the eye is normal and aligned. If you notice movement when switching off between the two eyes, then that deviation means that the patient is phoric.

Phoria is normal and it won’t disrupt everyday life. If the two eyes can work together in the end with the brain to achieve binocular vision, there is nothing to be concerned about. On the other hand, tropia is not normal and can lead to double vision since the misaligned eye won’t correct itself. If it is left untreated, impaired binocular depth perception can occur and the brain will begin to ignore the abnormal eye, resulting in a lazy eye. In some cases, individuals experienced permanent vision loss.

Prompt diagnosis and treatment of strabismus are critical. Children with strabismus may experience difficulty with reading or schoolwork, resulting in poor academic achievement. Adults may suffer from fatigue and headaches, leading to decreased attentiveness and productivity. Strabismus can even affect someone’s self-esteem. Someone can consider their turned eye as cosmetically displeasing and begin shying away from personal eye contact. With such severe consequences, it is important to be aware and cautious of the side effects to make sure that you or a loved one isn’t suffering from strabismus. Symptoms such as double vision, blurred vision, headaches, and tired eyes are common and should be checked out by an optometrist right away.

There are different treatment options depending on the patient and the severity of his/her strabismus. For very young patients, the goal is to allow binocularity to develop. The best way to do that is for optical correction via glasses. This will allow clear retinal images to be formed in each eye and won’t confuse the brain. A second option can be prism glasses. Objects viewed through a prism are displaced so it can center images that are angled differently from the strabismic eye, but this isn’t recommended since it is only a temporary fix. A third option is extraocular muscle surgery. This method should only be considered for patients whose best-corrected strabismic angle is still too large. Surgery can restore ocular alignment, but not one’s binocular vision.

The most favorable treatment for strabismic cases of low to moderate angle is vision therapy. Vision therapy consists of active eye exercises to possibly restore a patient’s ocular alignment and binocular vision by retraining the eye and brain to work together. Insight Vision Center Optometry offers vision therapy and we are very excited to help those, young or old, to better clearly see the world.