Eye-crossing

[Cap'n Refsmmat]

This thought just popped into my head randomly...

 

Why can most people cross their eyes but not move them otherwise independently? Surely if we can make the muscles cross our eyes, we can work out how to go the opposite direction.

[insane_alien]

i know someone who can move one up and the other down. damn freak that he is

 

you could probably do it if you kept on trying

[ecoli]

I can't cross my eyes The optometrist (sp?) told me that it was becasue my eye muscles are weak, and she taught me some exercises to strengthen them. But, I don't listen to doctors, and the exercises hurt, so I have resigned to not being able to ever cross my eyes.

[ydoaPs]

This thought just popped into my head randomly...

 

Why can most people cross their eyes but not move them otherwise independently? Surely if we can make the muscles cross our eyes, we can work out how to go the opposite direction.

 

Perhaps they can, but don't know it. It took me a few hours in front of a mirror to be able to.

[Dhondy]

This thought just popped into my head randomly...

 

Why can most people cross their eyes but not move them otherwise independently? Surely if we can make the muscles cross our eyes, we can work out how to go the opposite direction.

 

Crossing the eye is essentially an exaggeration of the physiological movement of convergence, as happens when you focus on an object very close to you. The musles involved are the medial recti, which are innervated by the oculomotor (III) nerve.

 

On the other hand, following an object with your gaze requires conjugate movement of both eyes, achieved by abducting one eye with its lateral rectus, innervated by the abducent (VI) nerve, and adducting the other eye with the medial rectus, innervated by the oculomotor nerve.

 

The way this conjugate movement is achieved is through a bundle of fibres on either side of the brainstem, called the medial longitudinal fasciculus (MLF), which connects the abducent nucleus of one side to the oculomotor nucleus of the other side.

 

Thus, when the lateral rectus of one eye contracts, the medial rectus of the other eye has to contract with it. Hence we can't disconjugate this movement, i.e. move them in opposite directions.

 

This may be lost in internuclear ophthalmoplegia, a condition affecting the MLF, as is found in brainstem stroke occasionally, but much more commonly in multiple sclerosis. Under this condition, conjugate movement in one direction is lost.

[KLB]

I can bring my eyes to a crossed position and then keep one eye "crossed" while moving the other eye independently in all directions. I can even switch between eyes by moving one eye independently then bringing it to the crossed position and moving the other eye independently. What really freaks people out is when I do a "figure eight" where by I cross my eyes, then move my right eye down, out, up and back to the center then do the same to the left eye.

 

Learning to do this was a matter of practice (and a few headaches in the beginning). As Dhondy expressed it is simply a matter of exaggerating the convergence of focus. One way to practice is to focus on the head of a pencil and then while moving it from the far right of one's vision to one's nose and then to the far left. After awhile one can learn to "focus" on an imaginary point and do the trick without any focus aid.