Final answer:
The AC/A ratio represents the relationship between eye focusing and alignment and is measured using changes in phoria at different distances with the help of lenses. Information provided does not include specific methods but environmental factors like extreme wind can affect the accuracy of the measurements.
Step-by-step explanation:
The heterophoria method is a clinical measure used to determine the relationship between accommodative (focusing) and vergence (eye alignment) systems, known as the AC/A ratio. It's not explicitly detailed in the provided information, but typically, it is calculated by measuring the change in phoria with a change in accommodation. by using lenses to stimulate accommodation while keeping the target at a constant distance, one can measure the phoria or the tendency for eyes to drift from perfect alignment at both far (usually 6 meters) and near (usually 40 cm) distances.
The difference in the measured phoria is correlated to the change in accommodation provided by the lenses, thus providing the AC/A ratio. Experimental errors such as environmental factors, like extreme wind, could impact the measurement by causing involuntary eye movements or squinting.