What are the characteristics of midline and symmetrical ocular movements?

Midline and Symmetrical Ocular Movements

Midline and symmetrical ocular movements are characterized by both eyes moving together in a coordinated fashion with central fixation, where fixation is described as "central, steady, and maintained" through smooth pursuit movements. 1

Key Characteristics of Normal Coordinated Eye Movements

Fixation Pattern

• Normal fixation is documented as "fixes and follows" or "central, steady, and maintained through a smooth pursuit" when assessing tracking movements 1
• The eyes should demonstrate smooth pursuit movements when following a target, with both eyes moving together without dissociation 1
• Fixation should be central (not eccentric), steady (not wandering), and maintained (not intermittent) 1

Binocular Coordination

• Coordinated binocular movements occur when both eyes move together in the same direction (version movements) without dysconjugate deviation 2
• Symmetrical movements require intact sensorimotor fusion, which integrates sensory fusion, stereopsis, and fusional vergence 1
• High-grade stereoacuity is associated with normal binocular alignment and coordinated movements 1

Assessment of Symmetry

The Brückner test provides objective evidence of symmetrical alignment by demonstrating equal red reflexes from both eyes simultaneously 1:

• Both red reflections should be equal in brightness and color 1
• The corneal light reflex should be centered in both pupils, not displaced 1
• Any asymmetry in the red reflex indicates misalignment or refractive differences 1

Clinical Examination Sequence

Testing should follow a specific order to avoid disrupting binocular function 1:

• Perform sensory function testing (stereoacuity, binocularity) before any dissociating techniques 1
• Assess binocular alignment before cycloplegia 1
• Avoid covering either eye during initial assessment, as this disrupts fusion and can unmask latent deviations 1

Distinguishing Normal from Abnormal Movements

Dysconjugate Movements (Abnormal)

• Dysconjugate movements occur when the two eyes fail to move together in a coordinated fashion 2
• This represents strabismus or ocular motor nerve dysfunction 2
• The angle of deviation may vary with gaze position (incomitance) or remain constant (comitance) 2

Nystagmus (Abnormal)

• Nystagmus consists of involuntary, rhythmic, to-and-fro oscillations that are distinct from smooth pursuit 2
• Manifest nystagmus is present constantly under binocular viewing and is typically symmetrical 2
• This differs from normal smooth pursuit, which is voluntary and controlled 2

Common Pitfalls to Avoid

• Do not perform cover testing or monocular visual acuity assessment before evaluating binocular function, as these dissociating techniques can disrupt fusion and alter the examination findings 1
• Do not confuse symmetrical vergence movements (both eyes moving in opposite directions for near targets) with dysconjugate movements, as vergence is a normal coordinated response 3
• Recognize that epicanthal folds can create pseudostrabismus, where eyes appear misaligned but the Brückner test shows symmetrical reflexes 1