Post-PRK muscular asthenopia and eccentric ablation

Objective To investigate the relationship between muscular asthenopia post photorefractive keratectomy (PRK) and eccentric ablation. Methods 16 eyes of 8 myopia cases whose muscular asthenopia was corrected b y subjectively accepted triangular prism after PRK with vision more than 0. 8 were followed up for 6 - 14 months. On the basis of data provided by the pre-PRK, post-PRK and their difference corneal topography, we calculated th e real corrected corneal diopter (D) with the Holladay formula and measured the ablating eccentricity (h) and its direction. According to the formula delta approximate to Dh, the prism effective value (delta) caused by the ec centric ablation was computed and compared with objectively accepted triang ular prism. Results The subjectively accepted prism was similar to values calculated fr om the formula. Their mean difference is 0.10+/-0.25. The direction of the subjectively accepted prism was in the direction of ablation deviation. Conclusions Eccentric ablation was the chief cause of post-PRK muscular vis ual asthenopia. The triangular prism effective value from eccentric ablatio n may be estimated by the formula delta approximate to Dh. We must pay atte ntion to the diagnosis, treatment and prevention of post-PRK muscular asthe nopia.