AC/A ratio || Gradient method || Calculated method 

The AC/A ratio, also known as the Accommodative Convergence to Accommodation ratio, is a clinical measurement used to evaluate the relationship between accommodation (focusing) and convergence (eye alignment). It assesses how much convergence the eyes produce in response to a given amount of accommodation.
Accommodation refers to the ability of the eyes to adjust their focus to see objects at different distances. Convergence, on the other hand, refers to the inward turning of the eyes to maintain single, binocular vision when viewing a near object.
The AC/A ratio is determined by measuring the change in eye convergence (in prism diopters) for a given change in accommodation (in diopters). This is typically measured using prism bar or prism flipper lenses.
During the assessment, the patient is usually asked to focus on a near target while the examiner introduces additional lenses to change the accommodative demand. The examiner observes the change in eye alignment, specifically the inward movement of the eyes, known as convergence. By comparing the change in convergence to the change in accommodation, the AC/A ratio is calculated.
A high AC/A ratio means that the eyes produce more convergence for a given amount of accommodation, indicating a strong relationship between accommodation and convergence. This is commonly seen in conditions such as convergence excess or esotropia, where excessive convergence occurs during near vision tasks.
Conversely, a low AC/A ratio suggests that the eyes produce less convergence in response to accommodation, indicating a weaker coupling between the two eyes. This can be seen in conditions such as convergence insufficiency or exotropia, where there is a reduced convergence response duringThe AC/A ratio is an important diagnostic tool in assessing and managing binocular vision disorders, particularly those related to the interaction between accommodation and convergence. It helps guide treatment decisions, such as prescribing prism lenses, vision therapy exercises, or other interventions aimed at optimizing the relationship between accommodation and convergence to improve binocular vision and reduce symptoms like double vision, eye strain, and headaches.
In summary, the AC/A ratio provides valuable information about the relationship between accommodation and convergence, allowing eye care professionals to diagnose and treat binocular vision disorders effectively.