I can't say what is happening. However, I would make a suggestion that if he doesn't have any allergy to sulfur, that he try MSM. It is very helpful in helping to make the eye more permeable and flexible so that debris, such as floaters can get out of the eye, and so the pressure does not build up in the eye, which may be causing the pulling sensation. I'd follow the directions on whatever brand you find, but be sure it is by a quality company. I'm not familiar with brands available in Europe. I'd also suggest tablets or capsules not powder for internal use. You may also want to try MSM eye drops, I believe they are still available in Europe. They can be very helpful as well.
But, if possible, have him go to the eye doctor for a thorough exam, as well as a neurologist if possible. Many brain function issues are manifest in the eyes.