Binocular instability (fusional vergence dysfunction) is characterised by low fusional reserves and an unstable heterophoria. The condition is given a historical perspective, noting that it can co-occur with dyslexia. Binocular instability is contrasted with decompensated heterophoria, noting that both conditions cause similar symptoms. Diagnosis requires a complete clinical picture and a simple algorithm is presented that assists the diagnosis of decompensated heterophoria and binocular instability. Diagnostic occlusion and investigative occlusion are summarised.
Pickwell's Binocular Vision Anomalies (Sixth Edition) 2022, Pages 91-95,