When your eyes work together, you have binocular vision. This allows you to see a single, clear image and helps you with depth perception.
Sometimes, the eyes don’t align perfectly. That’s when conditions like tropia and phoria come into play. Both involve some level of eye misalignment.
The main difference between a tropia and a phoria is that with a phoria, your eyes can usually compensate to maintain single vision. A tropia, however, is a manifest misalignment that’s always present.
If uncorrected, both tropias and phorias can cause eye strain, headaches, and reduce visual performance. In this article, we’ll explore the definitions, types, and differences between tropia vs phoria, as well as potential treatments to get your eyes back on track.
Defining Phoria: The Latent Misalignment
With tropia, the misalignment is obvious and always present. But with phoria, the misalignment is latent, meaning it’s only present under certain conditions.
What is a Phoria?
A phoria is a tendency for your eyes to drift out of alignment when they aren’t working together. When both eyes are open and working correctly, they’re aligned. But if one eye is covered, it drifts out of alignment.
The fusional vergence system compensates for this misalignment. Think of it as your eyes’ built-in correction system.
When your eyes are properly aligned, you have single vision. Your fusional vergence system works to maintain both alignment and single vision.
Decompensation happens when the vergence system is overwhelmed. When that happens, you may experience symptoms like eye strain, headaches, or blurred vision.
Types of Phorias
- Esophoria: Your eyes tend to turn inward, toward your nose, when they aren’t working together.
- Exophoria: Your eyes tend to turn outward, away from your nose, when they aren’t working together.
- Hyophoria: One eye tends to drift upward relative to the other when they aren’t working together.
- Hyperphoria: One eye tends to drift downward relative to the other when they aren’t working together.
Symptoms of Decompensated Phoria
When your phoria is decompensated, meaning your fusional vergence system can’t correct the misalignment, you may have symptoms like:
- Eye strain and headaches: These are often related to prolonged near work, like reading or working at a computer.
- Blurred vision: Because your eyes are constantly working to stay aligned, your vision may fluctuate or blur from time to time.
- Double vision (diplopia): In very severe cases of decompensation, you may see double.
- Difficulty concentrating: Visual discomfort can make it harder to focus.
Tropia (Strabismus): The Misalignment You Can See
Tropia, also known as strabismus, is a misalignment of the eyes that can be constant or intermittent. When someone has a tropia, one of their eyes turns away from the target they’re trying to focus on, even when both eyes are open and attempting to look at the same thing.
In tropia, the brain’s ability to compensate for misalignment is overwhelmed. The misalignment is always there, even if it isn’t always noticeable.
Types of Tropias
There are several types of tropias, depending on the direction of the eye turn:
- Esotropia: The eye turns inward toward the nose.
- Exotropia: The eye turns outward away from the nose.
- Hypertropia: One eye turns upward relative to the other.
- Hypotropia: One eye turns downward relative to the other.
Characteristics of Tropias
Tropias can also be described by how often the misalignment occurs and whether one or both eyes are affected:
- Constant vs. Intermittent: The eye turn may be present all the time (constant) or only sometimes (intermittent).
- Unilateral vs. Bilateral: The same eye may always turn (unilateral), or the eyes may alternate which one turns (alternating). In alternating tropia, each eye takes turns focusing on the target, and the other eye deviates.
Impact of Tropia
Tropia can have a significant impact on vision:
- Suppression: To avoid double vision, the brain may suppress the image from the deviating eye.
- Amblyopia (“lazy eye”): In children, suppression can lead to amblyopia, a reduction in visual acuity in the suppressed eye.
- Loss of depth perception: Tropia disrupts binocular vision, leading to a loss of stereopsis (depth perception).
Key differences between phoria and tropia
The biggest difference between a phoria and a tropia is whether the misalignment is constant or only happens sometimes.
- A phoria is a tendency for your eyes to misalign. Your brain can usually correct this misalignment using a process called fusional vergence.
- A tropia is a constant misalignment that your brain can’t correct.
Because a phoria is usually corrected by your brain, you may not have any symptoms unless you’re tired or stressed. When a phoria isn’t corrected, it can lead to:
- Eyestrain
- Headaches
Because a tropia is a constant misalignment, it can cause constant symptoms. Over time, your brain may start to ignore the information coming from one of your eyes. This is called suppression, and it can lead to a loss of depth perception.
Your eye doctor can diagnose a phoria by doing a cover test to disrupt your brain’s ability to correct the misalignment. A tropia can be diagnosed by simply looking at your eyes and seeing that they are misaligned.
Fusional Vergence Dysfunction (FVD) and its Relationship to Phoria and Tropia
Sometimes, your eyes are aligned, but your fusional vergence system – the system that keeps your eyes working together – is weak or not working as well as it should. This is called Fusional Vergence Dysfunction, or FVD.
The symptoms of FVD – eye strain, headaches, blurry vision, double vision, and trouble concentrating – are similar to those you might experience with decompensated phoria.
FVD can make the symptoms of phoria worse because it makes it harder for your eyes to compensate for the misalignment. If you have FVD, you’re more likely to experience a phoria that gets worse over time.
It’s important to note that in FVD, your eyes are aligned when you’re looking with both eyes open, unlike tropia, where there’s a clear misalignment that’s always present.
Fusional vergence has two parts: positive and negative. Positive fusional vergence allows your eyes to converge, or turn inward, while negative fusional vergence allows your eyes to diverge, or turn outward.
How are phorias and tropias treated?
Treatment options depend on the severity of the condition and how much it affects your comfort and vision. Here are some of the things your eye doctor may suggest.
Vision therapy
Vision therapy can help improve eye alignment and fusional vergence skills. The goal is to strengthen the muscles around your eyes and improve how well your eyes work together.
Some common vision therapy exercises include:
- Stick-In-Straw
- Brock String
- Barrel Card
- Lifesaver Cards
- Aperture Rule
- Eccentric Circles
Prism lenses
Prism lenses can correct or compensate for eye misalignments. They work by shifting the image you see, which allows your eyes to work together more comfortably.
Prism lenses can be used for both phorias and tropias to relieve symptoms and improve binocular vision.
Surgery
In some cases of tropia, surgery may be the best option, especially if vision therapy and prism lenses aren’t enough. The goal of surgery is to realign the eyes by adjusting the muscles around them.
Surgery is usually considered when the angle of deviation is large or when other treatments haven’t worked.
Addressing amblyopia (lazy eye)
If a tropia has caused amblyopia, it’s important to treat that, too. Treatment might involve patching the stronger eye to force the weaker eye to work harder.
Other treatments for amblyopia include atropine drops and vision therapy.
Frequently Asked Questions
What is the difference between Tropia and phoria?
The key difference lies in the visibility of eye misalignment. A tropia is a manifest misalignment, meaning one eye visibly deviates from the other, even when both eyes are open and attempting to focus. A phoria, on the other hand, is a latent misalignment, only present when one eye is covered or when the individual is fatigued or stressed. Under normal binocular viewing conditions, the eyes remain aligned in a phoria.
What is a phoria and tropia in the eye?
In simple terms, both phorias and tropias refer to conditions where the eyes don’t perfectly align. A phoria is a tendency for the eyes to misalign, kept in check by the brain’s effort to maintain single vision. A tropia is when this misalignment is always present and noticeable, despite the brain’s efforts.
What is the tropia of the eye?
The tropia of the eye describes the direction of the eye’s deviation. For example, esotropia means the eye turns inward (towards the nose), exotropia means the eye turns outward (away from the nose), hypertropia means the eye turns upward, and hypotropia means the eye turns downward.
Can a phoria turn into a tropia?
Yes, in some cases, a phoria can decompensate and turn into a tropia. This can happen if the brain’s ability to compensate for the misalignment weakens, often due to fatigue, illness, or stress. It is important to consult with an eye care professional if you notice a sudden change in eye alignment.
Key Takeaways
Phorias and tropias both involve eye misalignment, but the key difference is whether your eyes can compensate. With a phoria, your eyes can compensate to maintain alignment and single vision, although this takes effort. With a tropia, one eye is always misaligned, even when you’re trying to focus.
Getting a proper diagnosis and treatment is important for both phorias and tropias. Even though your eyes compensate with a phoria, it can still cause discomfort and affect your vision. Luckily, there are things you can do to make things better.
Vision therapy can help strengthen your eye muscles and improve coordination. Prism lenses can help realign images, and in some cases, surgery may be an option. A comprehensive eye exam is the first step. It’s crucial to assess your binocular vision and identify any underlying issues that could be contributing to a phoria, tropia, or other form of Fusion Vergence Dysfunction (FVD).
Early detection and intervention can make a real difference in visual outcomes and your overall quality of life, so don’t hesitate to get your eyes checked!