Our nervous system sends signals around our bodies that control our subconscious activities such as breathing, and our conscious activities such as physical movement Our reflexes and the functioning of our or organs are controlled by these mainly electrical impulses (vibrations).
Our existence, our health and well-being depend upon a constant stream of these signals between our brain and the many parts of our bodies. When the signals are interfered with, then our bodies react abnormally.
Drugs, alcohol, poisons, stress and illness can all affect these signals, and have an adverse effect on our bodies.  Normal vibrations can often be restored through natural treatments using sun, air, water diet and the application of natural substances. External factors can affect the impulses flowing around our nervous systems. 
The transcutanial electrical nerve stimulator (TENS) device generates electrical vibrations externally that can modify the vibrations in our nervous systems to reduce pain.
It is quite possible that the vibrations of our nervous system, reflecting illness, health and our lifestyle could be recorded as patterns in the iris. The immediate appearance in the iris of patterns that reflect trauma, such as an accident give credibility to that theory. In future,  the science of iridology may well be revealed through an understanding of the relationship between vibrations and patterns in the iris.

An Additional Thought on the Vibratory System by Sandy Carter

Since we know that a TENS device has an effect on the impulses traveling around our nervous system, this might give us a way of proving that the iris records
vibrations of our nervous system. 
If photographs were taken of the iris for a number of volunteers, who had never used a TENS device, but who then used it extensively over a period of time.  The iris could be examined afterwards and compared to the photographs, to  see whether it had recorded any changes that could be related to the vibration affected by the TENS.  If so,  then it would be possible to conduct more selective experiments with the TENS devices that might prove the theory beyond reasonable doubt.