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Suppose we want to learn more about our binocular vision problems or our child’s. In that case, there are some concepts that we may have heard our optometrist mention, but perhaps we still need to fully grasp them. We are referring to vergence: convergence and divergence.
In this article, we would like to learn more about the concepts of convergence and divergence and why they are so important to work on our binocular vision.
When we look at an object at a far distance, our visual axes are parallel and have a 0 angle, which means that we are in a position of relaxation, also known as divergence.
However, when this object approaches us, our visual axes have to converge toward the object, which prevents us from seeing it twice. As the object approaches us, the angle between our visual axes will be sharper since we converge. This allows our brain to calculate the distance between the object and us.
Binocular Disfunctions Related To Convergence and Divergence
According to the Catalan Association of Optometry and Visual Therapy, the different binocular dysfunctions are as follows:
Basic exophoria: latent deviation of the visual axes outwards at near and far.
Basic endophoria: unlike the previous one, it is a latent deviation of the visual axes inwards at near and far.
Convergence insufficiency: difficulty in stimulating near convergence and maintaining ocular alignment.
Convergence excess: difficulty in relaxing convergence after near activities.
Divergence insufficiency: difficulty in relaxing convergence at a distance.
Excessive divergence: difficulty in stimulating near convergence and maintaining ocular alignment.
What are phorias?
Ocular phoria refers to the lack of alignment of the visual axes, but it is not possible to appreciate it with the naked eye. It can only be revealed through a visual test.
It is a latent deviation that manifests only when no visual stimulus exists in one of the two eyes. Hence, the eyes lose coordination between them, and there is no integration in the brain.
To understand it better, we like the example given by Rosa M. Garcia in her blog. She indicates that phoria refers to an ocular deviation but internal, which is impossible to notice with the naked eye and depends on the mental maps produced in our brain. It does not rely on the eye muscles.
Phoria appears when there is a mismatch between what we interpret from our internal map regarding the location of space and how the environment is really arranged.
That is to say, if an object is at a certain distance from us, say 30 cm. We can see it at 30 cm, which means there is a balance between the reality of the environment and what our internal map interprets. This, in turn, means there is no movement in the eyes, and they are aligned.
However, suppose the same object is still 30 cm away from us, but our internal map tells us that the object is closer than it really is (30 cm). In that case, it means that there is a phoria. A movement in the alignment inwards, i.e., endo.
On the other hand, if we see an object 30 cm farther away from us, it translates as a phoria moving outwards, i.e., exo.
What are vergences?
Vergences are alterations related to the coordination between the two eyes to keep both at a fixed point.
As Rosa M. Garcia points out, Vergences, in turn, are related to the capacity of accommodation, i.e., focusing.
If an object is less than 6 meters away, we use convergence, which will be greater as the object gets closer. Divergence appears when we direct our gaze from a near point to a distant one.
Convergence is related to the ability to stimulate accommodation when looking at a close object, just as the focus of a camera does to ‘see’ it sharp. (single image and not double).
And divergence, on the other hand, is related to the ability to relax accommodation when viewing a distant object. The focus is relaxed to see it sharp and single.
What is convergence?
If we look up the term convergence in a dictionary, we will see that it is defined as the union or confluence of two or more things at a given point. The opposite of convergence is a separation or divergence.
Suppose we want to fix our eyes on a particular object. In that case, it is necessary to align and fixate both eyes simultaneously on the point where the object is located.
To perform the proper eye movement that allows this action, we use 6 eye muscles. These eye muscles need to work properly to get information to the brain from the image of each of the retinas. This ability is called ocular convergence.
As the object changes position and gets closer, the convergence movements also change the gaze direction of both eyes towards the nose.
What is convergence insufficiency?
Convergence insufficiency (CI) refers to the inability to keep both eyes working together (binocular function) at a near distance due to a muscle coordination problem. One eye likely tends to turn outward when focusing on a near object (exophoria).
For more information on the concept of convergence insufficiency, we can review the following article in the Revista Cubana de Oftalmología.
What is convergence excess?
Excess convergence (EC) is a binocular disorder characterized by an inward deviation (endophoria) in near vision. And it is characterized by the ocular internal rectus muscles performing more force than they should, which overloads the ocular muscles when performing near-vision activities. The eyes make an excessive accommodative effort.
What is divergence?
Divergence, is defined as a separation of two or more things with respect to a given point.
What is divergence insufficiency?
Divergence insufficiency (DI), like with excess convergence, the eyes converge more than they should, but DI refers to a lack of precision in the transition of gaze from a point near to one that is far away. This binocular dysfunction presents high endophoria at a distance and slight endophoria and even exophoria nearby.
We can continue reading this Medigraphic article for further information on divergence insufficiency.
What is convergence excess?
Excess divergence (ED) refers to an anomaly in binocular vision, just like the previous ones. It is similar to convergence insufficiency, except it presents an intermittent distance exophoria.
Symptoms of binocular disturbances
As indicated by the College of Opticians and Optometrists of Andalusia, among the symptoms that can cause convergence and divergence problems we can suffer from:
- blurred vision
- double vision
- difficulty in reading
- difficulty concentrating
- tired eyes
This is why we cannot forget that if we observe any symptom related to binocular alterations, we should consult an eye doctor so that they can perform a complete check-up and consider which treatment is the most appropriate for our particular case or that of our child.