Cogan’s twitch sign
- * The patient is asked to maintain up gaze for 20–30 seconds which fatigues the superior rectus and inferior oblique muscles.
- The patient is asked to follow the examiner’s finger below the horizontal and back to the horizontal.
- The lids will be seen to rise above the iris and then settle to their normal position.
- The law of equal innervation for yoked muscles (Hitzig’s law) states that muscles that work in tandem receive equal innervation.
- If the superior rectus and inferior oblique are fatigued in up gaze, they receive maximal innervation: this increases the innervation to the levator palebral muscle (yoked muscle) which causes the upper lid to retract away (increased lid retraction) from the iris on up gaze (more than is necessary) and then settle to normal position (a Cogan’s twitch).