Compensatory versus non-compensatory types in myopic acute acquired comitant esotropia: a new classification based on fusion ability at the far point

Purpose To propose a novel classification of acute acquired comitant esotropia (AACE) with myopia based on fusion compensation ability at the far point (FP) without myopia correction (MC) and to investigate its pathogenesis in relation to eye-use habits. Design A retrospective case-control study. Methods This study enrolled 105 myopic AACE patients and 107 control subjects with simple myopia. Data collected included refractive error, angle of deviation (measured by prism and alternate cover test (PACT) and Maddox prism test (MPT) at distance and near), and detailed eye-use habits. AACE patients were categorized into compensatory ( n = 92) or non-compensatory ( n = 13) groups based on their ability to maintain binocular fusion at the FP without MC. Results A total of 98.10% of AACE patients neglected MC during prolonged near gaze before onset, a rate significantly higher than controls (13.08%). The cohort was divided into compensatory and non-compensatory groups. The compensatory group (87.62% of patients) exhibited distinct features: larger distance versus near deviation ( P < 0.001), greater MPT than PACT at distance ( P < 0.001), and near-zero deviation at the FP without MC. In this group, the convergence requirement at the FP (CRFP) showed no significant difference from MPT at distance (MPTD) ( P = 0.054) and was positively correlated with both MPTD and PACT at distance (PACTD) ( P < 0.05). In contrast, the non-compensatory group (12.38%) had a younger onset age, lower refractive error, larger deviation angles, and worse stereopsis. Conclusion Prolonged near gaze without MC is a critical risk factor for myopic AACE. Classifying patients based on fusion compensation at the FP reveals two distinct subtypes with different clinical profiles. The compensatory type likely represents an abnormal adaptation to excessive convergence demand, whereas the non-compensatory type may indicate a decompensated mechanism. This new classification provides valuable insights for etiology and management.