Your Iyengar Yoga teacher may have instructed you to cover your eyes with a blanket or eye pillow during deep relaxing restorative yoga poses – particularly Savasana. Do you want to know the scientific reason for this?
Covering your eyes this way would prevent any light from falling on the eyes reducing the external stimulation. The eye pillow (a small one and not very heavy), in particular, would damp out extraneous motions of the eyes. This would prevent any possible neural action – providing deep relaxation.
What really happens is this. The mild pressure on the eyes and their orbits will activate what is called ‘Oculocardiac reflex‘. This is also known as ‘Aschner reflex’ or ‘Ocular-vagal reflex’. The Oculocardiac reflex causes a decrease in pulse rate associated with traction applied to extraocular muscles (that control the eye movement) and compression of the eyeballs. With the pillow, the periphery of the eyes receives external pressure, further stimulating this reflex. The heart slows down, which in turn lowers the arterial blood pressure within the skull. This results in relaxation through the activation of the parasympathetic nervous system. With the reduced heart rate, many physiological processes slow down as well, helping the person move to a deeply relaxed state.
Without the eyes covered in restorative poses, the stimulation on eyes may lead to excitation within the reticular formation. This may activate the sympathetic nervous system (fight-and-flight) and reduce the relaxation effect of these poses.