secondary deviation
The measured strabismus angle when the paretic or amblyopic eye is forced to fixate and the normal eye assumes the deviated position.
Full Definition
Secondary deviation represents the strabismus angle measured when the patient fixates with their weaker or paretic eye, causing the normal eye to deviate. In paralytic strabismus, the secondary deviation is characteristically larger than the primary deviation due to increased innervational effort required by the weak muscle (Hering's law of equal innervation). This difference between primary and secondary deviations is pathognomonic for paralytic disorders and helps distinguish them from comitant strabismus where both measurements are equal.
Usage
Usage note: Essential to measure in suspected paralytic cases; compare with primary deviation to assess for incomitance.
In Context
- "The secondary deviation of 45 prism diopters compared to a primary deviation of 20 confirmed the sixth nerve palsy diagnosis." — Paralytic strabismus evaluation
- "Surgical planning required consideration of both primary and secondary deviation measurements in this paralytic case." — Pre-operative surgical planning