Strabismus is one of the commonly encountered ophthalmological diseases. Recessions and resections of the medial or lateral rectus muscles, the most commonly used procedures for the correction of horizontal comitant strabismus have effect on the vertical palpebral fissure height (VPFH). The aim of the study was to assess the effect of horizontal strabismus surgery on the palpebral fissure height. This was a prospective study included 30 patients (43 eyes) who had horizontal strabismus. Patients were divided into two groups: group A who underwent recession surgery, group B who underwent recession-resection surgery. Vertical eyelid fissure width measurements were compared before and after treatment. Digital imaging analysis and the metric ruler were used to measure vertical palpebral fissure height. Regarding to vertical palpebral fissure height, no significant difference was found between group A and B (P.>0.05). Within group A, a significantly higher mean was found at 3 months after surgery, in comparison to 2 weeks after surgery (P.≤0.05). Our study showed that unilateral or bilateral horizontal rectus muscle recession may induce a post-operative widening of the vertical palpebral fissure width. Recession-resection surgery also may affect the vertical palpebral fissure height.