Squinting and astigmatism
Squinting shouldn’t be mistaken for astigmatism. With squinting there’s a problem with the position of the eye ball, whereas astigmatism is an optical problem. Here’s an explanation:
Our eyes each have six muscles, whose job is to turn the eye and keep it in its resting place. If one of those muscles is too strong or too weak, there’s a danger that the eyes can’t simultaneously turn or both stay in a straight line when resting. Squinting can occur horizontally (pointing inside or out), vertically (pointing up or down) or it can appear with a combination of the two. The degree of squinting depends on the distance and angle of vision that the eye is focusing at.
Obvious squinting (Strabismus)
This kind of being cross eyed is visible to everyone. In adults, a correction can’t bring back binocular vision, but it can have a social impact. Squinting people can become victims of prejudicial comments.
Hidden squinting (Forie)
Hidden strabismus is much more common than obvious squinting. It can become more obvious, for example, when the person is tired.
Sometimes it is difficult to recognize hidden squinting because the symptoms often show as general unwellness or they’re being seen as malfunctioning position of the eye. The fatigue of the eye can cause a sense of unease while reading: the words seem to jump around, this can cause headaches, or pains “behind” the eyes. The reader doesn’t feel like reading anymore.
While working, hidden squinting can cause double images show on screen. Hidden squinting can only cause problems when the person affected is in his/her 40’s or 50’s, That’s the age when the eye muscles are loosing some of their strength.
Accommodation and squinting
Eyes have the ability to accommodate the vision to different distances. Without this ability we could only focus on one single distance. But with age this ability deteriorates. Whenever the eye focuses it also turns inwards or it converges. This can worsen (to the inside) or minimise (to the outside) the squinting.
Lens strength and squinting
Depending on the strength of the lenses in the glasses, the squinting can get better or worse. Ideally the strength of the lenses and/or the prisms correction corrects the squinting.
But in the worst case, the lens strength can cause other symptoms with the underlying hidden strabismus.
An example of this is a short-sighted man in his 50’s, who squints to the outside. If his short-sighted vision is corrected without taking the hidden strabismus into account, he could end up with more problems. As he is wearing varifocals and is squinting at the same time, the vision of one eye is blurred, as this eye is looking across the corrected lens. As a result of that the man needs to turn his head in order to have clear, sharp vision with that eye.
Contact lenses and squinting
The impact on the eyes is different when wearing contacts when being cross-eyed, because the contact lenses don’t enlarge nor minimize. As a result the eye muscles react differently than to lenses in glasses. Unlike with glasses you can’t apply a prism correction. Having the contacts tested by an expert is probably the easiest way to find out whether or not they are suitable for you.
Astigmatism or corneal irregularity
Astigmatism can occur on the cornea or inside the eye or even a combination of both. If you only have an irregularity on the cornea, the eye is unable to focus in different directions and therefore multiple corrections in various directions are needed. With a so-called cylinder correction and an added angle to the axis (for example cylinder -75 in axis 90 degrees) you can adjust the lenses or contacts.
If a person is short sighted and has astigmatism the lens strength could be the following:
-1.00 dpt -0.75 90°. The person has a correction of -1.00 vertical and -1.75 horizontal. The strength changes from one side to the other and back. This can be indicated as: -1.00 -0.75 90° or -1.75 +0.75 0°. Experts have still not agreed on one of the two notations.
On a prescription for lenses, there are multiple numbers indicated, which can easily be confused. In this article I’ve tried to explain two of those, because these are often being mixed up and therefore people get confused. I hope my explanation was helpful.