Diplopia as a complication of laser in situ keratomileusis surgery.

A case is presented of a patient with high myopia who developed vertical binocular diplopia after decentred laser in situ keratomileusis (LASIK) surgery with associated decompensation of pre-existing exophoria into an exotropia. A 40-year-old man underwent LASIK surgery for high myopia in his right eye. Preoperatively, he was approximately -26.00/-2.00 x 35 degrees with visual acuity of 6/12(-2) in that eye. He also had an asymptomatic exophoria. After LASIK surgery, he achieved a refraction of -3.25/-0.50 x 80 degrees with 6/21 best-corrected visual acuity. He also developed binocular diplopia. The ablation zone had been decentred upwards and there was also an exo- and hypo-deviation of his right eye. He was able to superimpose the two images in free space with vertical and horizontal prisms.A hard contact lens also resulted in superimposition of the two images. Vertical decentration of the ablation zone can induce a vertical prism effect after LASIK surgery and result in vertical diplopia. This together with abnormal optics also caused loss of best-corrected vision and decompensation of his pre-existing exophoria into an exotropia.