SIRC (Surgically Induced Refractive Change) is mathematical subtraction of refraction (at spectacle plane) between the Sphere-EQuivalent (SEQ) before and after laser refractive surgery (laser or keratotomy).
SIRC is a necessary value in many biometric formulas for eyes that have undergone refractive surgery. It is also called “Rx change“.
Before refractive surgery: Sph -4 cyl -2 (180) – Preop SEQ = -5 D
After refractive surgery: Sph 0 cyl -1 (180) – Postop SEQ = -0.5 D
SIRC = (-5) -(-0.5)= -4.5 D
Pay attention to SimK after refractive surgery: it must be evaluated after any regression related to epithelial regrowth.