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Deviation of the Eyes – How Much is Too Much?


3 min


Deviation of the eyes

How much eye deviation is considered acceptable, and when does it become a cause for concern? In this blog post, we’ll explore the fascinating world of eye movement and delve into the question of how much deviation is too much.

Normal Eye Movement

In a typical scenario, our eyes move smoothly and symmetrically. When we engage in a conversation or interact with our environment, our eyes naturally shift to focus on different points of interest. Normal eye movement involves a combination of:
saccades (rapid jumps between fixation points),
pursuits (smooth tracking of moving objects),
– and fixations (pauses on specific points).

What is Deviation of the Eye

Eye deviation refers to any noticeable misalignment or asymmetry in the movement of the eyes. This can manifest as one eye moving differently than the other, a wandering gaze, or involuntary eye movements that disrupt normal coordination. Deviation can be subtle or pronounced, and it may occur intermittently or persistently.

Family Ocular History

When starting examining visual system at the eye care specialist it is very important to start with anamnesis. It is one of the most important starting points of the thorough eye exam. The chance that an anomaly is found is often connected to the family ocular history.

For example, if a parent used to occlude one of the eyes as a child and at the exam they are not sure which eye they had to occlude, it is most probably that the occluding therapy was successful.

Occluding is needed when one eye deviates from the ideal axis in regard to the other eye. The most common eye deviations are when one eye is inclined towards the nose – nasally (ESO deviation) or outwards – temporally (EXO deviation). The less common deviation is vertical, however, it is more symptomatic. 

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Understanding Deviated Eyes and Deviation Intensity

The deviations are categorized in the intensity of the deviation or measured by the angle or prism dioptres. The visual system is so advanced that even in cases when the two eyes are not aligned ideally, the picture on the retina and therefore in the visual cortex is perceived as one. 

The problem occurs when one eye is declined to such extent that the pictures projected of the two eyes on both retinas are not merging and are not perceived as one when double vision kicks in.

When the image on the retina is projected on the corresponding points on the retinae, the vision is then comfortable and single with the presence of stereopsis (depth perception). If the angle of declination is too big, then the single image is not possible. In this case, the visual system neglects the image that is declined in regard to the other to perceive only one single image.

So is there no problem anymore? When suppressing one eye, what is the most common result in the development stage of the vision (e.g., between 3 and 8 years of age)? The deviations are very difficult to recognize. Small deviations are normal and acceptable.

DIY Eye Deviation Check

We know a few ways how to recognize bigger deviations on our own. With the Cover-Uncover test, we might find out some deviations. The procedure is as follows:

  • Find an occlude in the shape of a small racket (e.g., a wooden spoon).
  • The test person is focused on an object more than 6 meters away (e.g., a door handle).
  • Start the test by covering one eye (with an occluder) and precisely observing the unoccluded eye if there is any deviation.
  • Proceed with covering the second eye and again precisely observe for any deviations.
  • Repeat these steps a few times to be certain.
  • If there is no deviation, the test is negative, so there is no obvious error or anomaly.
  • If the eye is declined nasally, inwards, then we get the EXO deviation; in case of declination temporally, outwards, then we get ESO deviation.
  • The same test can be done at near also, for the target, get something small (e.g., a pencil top).

In case of uncertainty or bigger declinations, we suggest you visit an eye care specialist for further and more thorough testing.

Frequently Asked Questions

How are eye deviations categorized?

Deviations are categorized based on the intensity measured in angles or prism dioptres, helping understand the severity of misalignments in the visual system.

Can the visual system compensate for misalignments between the eyes?

Yes, the visual system is advanced enough to merge images on the retina, providing a single and comfortable vision. However, significant misalignments may lead to double vision or suppression of one image.

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