## Understanding Comitant Strabismus **Key Point:** In comitant strabismus, the PRIMARY deviation (deviation of the affected eye) is ALWAYS greater than or equal to the SECONDARY deviation (deviation of the normal eye). The statement that secondary deviation is greater than primary is the hallmark of incomitant (paralytic) strabismus, not comitant. ### Distinguishing Features of Comitant Strabismus | Feature | Comitant | Incomitant (Paralytic) | |---------|----------|------------------------| | Primary vs Secondary deviation | Primary = Secondary or Primary > Secondary | Secondary > Primary | | Muscle structure | Normal | Paralyzed/weak | | Angle of deviation | Constant in all gazes | Varies with direction | | Diplopia | Absent (suppression) | Present | | Head posture | May be abnormal | Abnormal (to minimize diplopia) | | Onset | Usually childhood | Any age, often acute | **High-Yield:** The mnemonic **"COMITANT = CONSTANT"** — constant angle in all directions of gaze, constant primary > secondary deviation, and constant suppression (no diplopia). **Clinical Pearl:** In comitant strabismus, the brain suppresses the image from the deviating eye to avoid diplopia, especially if onset is before age 6–8 years. This is why patients rarely complain of double vision. ### Why the Other Options Are Correct - **Extraocular muscles are normal:** True — comitant strabismus is a disorder of innervation/binocular control, not muscle paralysis. - **Angle constant in all directions:** True — this is the defining feature that distinguishes comitant from incomitant strabismus. - **Diplopia absent in long-standing cases:** True — suppression develops, especially in childhood-onset cases. [cite:Parson's Diseases of the Eye 21e Ch 11]
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