Fixation Release in Dissociated Strabismus: Dissociated Vertical Deviation as an Uncorrected Shared Upward Drive, and Related Phenomena

Fixation Release in Dissociated Strabismus: Dissociated Vertical Deviation as an Uncorrected Shared Upward Drive, and Related Phenomena Author: Dr. Ghassan Ahmed Mubasher MohamedsalihAffiliation: Neuro-Ophthalmologist, Hamad Medical Corporation, Doha, QatarEmail: Gmohamedsalih@hamad.qaORCID: https://orcid.org/0009-0000-7926-3150 Description This theoretical paper proposes a unified framework for understanding dissociated strabismus and related ocular motor phenomena through the principle of fixation-dependent release of latent directional motor biases. It examines dissociated vertical deviation (DVD), inferior oblique overaction (IOOA), dissociated horizontal deviation (DHD), the Bielschowsky phenomenon, the Heimann–Bielschowsky phenomenon, and fusion maldevelopment nystagmus. The central hypothesis interprets DVD as a motor shadow of fixation. Drawing on the bilateral organization of the vertical elevator system described in the author's Upward Alliance theory, the model proposes that both eyes receive a shared upward motor influence, whereas a depressor-directed correction is generated separately for the eye maintaining effective fixation. When binocular constraint is weakened, the released eye retains the shared upward influence without the corresponding fixation-dependent correction, producing the characteristic dissociated elevation. The framework further proposes that IOOA may represent a three-dimensional vertical–torsional expression of the same motor organization, while DHD reflects a related horizontal imbalance. The graded Bielschowsky response is interpreted through changes in fixation-dependent corrective activity. The Heimann–Bielschowsky phenomenon is considered a provisional extension involving instability of vertical motor control, while fusion maldevelopment nystagmus is integrated into the framework using the cortical motion-imbalance mechanism proposed by Tychsen and colleagues. The paper critically examines alternative explanations, including Brodsky's visuo-vestibular dorsal light reflex theory, Guyton's nystagmus-blockage hypothesis, and a passive mechanical-equilibrium null model. It develops experimentally testable predictions involving fixation state, retinal illuminance, graded sensory attenuation, binocular eye-movement coordination, ocular torsion, and head and body orientation. The proposed framework is intended as a theoretical contribution to ocular motor physiology and neuro-ophthalmology. Its mechanisms and extensions remain hypotheses requiring experimental validation.