Does astigmatism alter with cycloplegia?

PURPOSE: To determine the effect of the cyclopentolate 1% on the cylindrical and spherical components of the refraction. METHODS: Three hundred seventy-five eyes of 195 subjects, including 74 males and 121 females, aged from 3 to 59 years were refracted before and 30 min after cyclopentolate 1% eye drop instillation. To compare cylindrical data, power vector analysis (J(0) and J(45) cross cylinder) was applied. RESULTS: A statistically significant difference between the J(0) values of the noncycloplegic and cycloplegic refraction was revealed (P = 0.006) while the J(45) values did not significantly differ. 95% limit of agreement for dry and cycloplegic values of the J(0) and J(45) were −0.22 to 0.25 and −0.19 to 0.20, respectively. Astigmatism difference was separately analyzed in emmetropic, myopic and hyperopic eyes. The J(0) difference was significant (P = 0.014) only in hyperopic eyes. Spherical equivalent (SE) values in cycloplegic refraction were significantly more hyperopic than those yielded in dry refraction by mean difference of +1.16 ± 1.20 diopters (P < 0.0001). Spherical equivalent difference (SED) values were negatively correlated with age. CONCLUSIONS: Our findings indicated that cycloplegic drops caused a statistically significant shift in the “with the rule” and “against the rule” astigmatisms, although the oblique astigmatisms remained unaffected. Further research with larger sample sizes are needed to answer what mechanisms are involved in changing cylinder with cycloplegia.