Panic attacks are characterised by extreme anxiety of an anticipated threat, which may be a real or imagined threat on the part of the patient to themselves or to others. Bowan describes the use of vergence therapy using the visual-vagus connection as a possible treatment for a panic attack. A panic attack stimulates the sympathetic nervous system associated with increased stress, which results in symptoms of increased heart rate, chest pain (non-cardiac in origin), tremor, increased breathing rate, difficulties with speech, nausea, and perspiration.

The parasympathetic nervous system then overcompensates and can cause fainting due to a sudden decrease in blood pressure and heart rate via the vagus nerve. The vagus nerve supplies parasympathetic fibres to many organs, and the physiological responses are known to be fairly instantaneous. The Valsalva manoeuvre, which is an attempt to breathe out through a closed glottis, also activates the vagus nerve. This can effectively reset the vagal fibres to the heart, steadying both blood pressure and heart rate.

The oculo-cardiac reflex (OCR) is often discussed as a method that results in bradycardia, decreasing the heart rate. Knowledge of this reflex has been used in medicine and veterinary science. In medicine, care is taken during strabismus surgery not to overstimulate the extra-ocular muscles (EOM), as this results in bradycardia. Prolonged stimulation can result in asystole. Voluntary convergence stimulates the EOM insertions, especially those of the medial recti.

reference: Role of Optometry in the Management of Vision and Ocular
The health of Patients with Mental and Emotional Disturbance:
Part 1; Elizabeth Muller, B.App.Sc. (Optom), North Altona, Australia