When light hits the back of the eye, tiny cells convert the light into nervous impulses.   These travel across the retina, through the optic disc, to the brain. 

 Glaucoma is a group of diseases which cause these nerves to become damaged.  When this happens the nerves become unable to send the impulses.  This leads to blind spots, initially out of the corner of the eye. 

 If the condition is not treated, the blind spots get larger and can lead to blindness.  It is known that pressure in the eye is an important factor in this condition.  The production and drainage of "water" in the front of the eye affects the pressure.  If this gets out of balance the pressure in the eye can increase.   Glaucoma can be controlled by using eye drops to reduce the pressure in the eye.