Syntonics, also known as Optometric Phototherapy. It is the branch of ocular science dealing with the safe application of selected visible-light frequencies through the eyes. It is used for eye conditions like focusing problems, ocular discomfort and headaches, light sensitivity, visual field constriction, visual attention difficulties, stress or emotional related visual disorders, and certain visual problems related to traumatic brain injury.

The goal of Syntonics is to improve vision problems by balancing the sympathetic and parasympathetic nervous system. The yellow, orange and red ends of the visible spectrum stimulate the sympathetic nervous system; and the blue, indigo and violet ends stimulate the parasympathetic nervous system. Green is the balance frequency stimulating the sympathetic and parasympathetic nervous systems equally. Light entering the eyes not only serves vision, but also travels to other important brain regions. It is believed that applying certain frequencies of light by way of the eyes can restore balance within the body's regulatory centers, thereby directly affecting the source of visual dysfunctions. This balance is referred to as syntony.

Syntonics technique, using colored filtered light, was one of the first that treated problems by shining light directly into the eyes. Syntonics was developed by an American scientist, Dr Harry Riley Spitler, whose approach was to treat the body by way of the eyes, thereby using the shortest pathway to the brain. His research showed that different colors of light entering the eyes can affect the balance of the body and its functions. Syntonics has been shown to improve a patient's visual field and can also benefit the immune system and emotional state.

In a Syntonics treatment, the patient sits in a darkened room in front of a fixed lamp that delivers colored light of specific frequencies. A treat­ment lasts about 20 minutes and is generally repeated once a day for about three weeks.

Syntonics has been used clinically for over 60 years. Jacob states: ‘While medical science has shown that light has a profound stimulatory and regulatory effect on all of the body’s vital functions, optometric phototherapy has found that specific portions of the visible spectrum act as rebalancers of these vital functions. Light may well be the major nutrient which feeds the evolution of all life.’