Purpose: To study the validity and reliability of subjective refraction, predicted phoropter refraction (PPR) measured by Zywave aberrometer, and final surgical plan applied for laser vision correction.
Methods: This prospective study was conducted on 94 myopic or myopic astigmatic eyes (48 patients) who were candidates for refractive surgery in Negah Eye Hospital from April 2012 to July 2012. Subjective refraction and PPR by Zywave aberrometry were measured and complete ophthalmic examination were performed in all participants. Surgical correction of refractive error was then planned, based on the subjective refraction and the patient’s age. The patient underwent customized surface ablation using the Bausch & Lomb 217 z excimer machine. At 6 months postoperatively, subjective refraction was measured to determine residual refraction. The “exact refraction” was defined as the refraction used for surgery added by postoperative residual refraction. This “exact” amount was compared with the preoperative subjective refraction, PPR and surgical plan.
Results: The mean difference between “exact” myopia and subjective refraction, PPR, and surgical plan were 0.11±0.51D (P=0.03), 0.18±0.70D (P=0.01), and -0.06±0.46D (P=0.01), respectively. The difference between “exact” myopia and myopia in subjective refraction and PPR was significant.
The mean difference between “exact” astigmatism and astigmatism in subjective refraction, PPR and surgical plan were statistically significant (P<0.05). The lowest difference was between “exact” astigmatism and PPR astigmatism. (P=0.021). The correlation coefficient between “exact” myopia and subjective, PPR, and surgical plan myopia were 0.95, 0.92 and 0.96, respectively. Also, the correlation coefficient between “exact” astigmatism, subjective, PPR and astigmatism in plan were 0.89, 0.83 and 0.90 respectively. As indicated, the strongest correlation was observed between excat myopia and astigmatism, and PRP myopia and astigmatism.
Conclusion: The mean myopia measured by Zywave aberrometer was comparable with exact myopia. Planning the myopic refractive correction based on the patient’s subjective refraction and adjusted by age was the most accurate method to achieve the least amount of residual refraction. There was no significant difference between exact astigmatism and preoperative astigmatism measured by the three methods.