Comparison Of The Accommodation And Vergence Parameters With Two Different Correction Methods For Myopia

ObjectiveIn this study, different visual parameters that characterize the accommodative and vergence function were evaluated in myopes when their myopia was corrected with either spectacles or soft contact lenses (SCL), to determine if there were any difference when these two correction methods were used in clinical practice, and whether the differences agreed with theoretically distinction of these two correction methods. This study could also provide useful information concerning the changes when SCL were used, and whether these changes could be significant factors in the onset or progression of myopiaMethodsData were recorded from55myopic subjects, all of whom were students of Tianjin Medical University, with the informed consent of them from Mar. to Jun.2012. They all have the experience of using SCL as the correction method in their daily life and their age range from20to26. All patients with systemic disease, anisometropia, strabismus, high astigmatism (higher than1.00D), amblyopia or ocular disease were excluded.For measurements made with a spectacle correction, each subject were corrected with a simple trial frame or phoropter (vertex distance=12mm). The parameters measured with a spectacle correction or a SCL correction were monocular and binocular accommodative parameters (including accommodation amplitude, accommodative facility, and accommodative response), and the vergence parameters (including negative relative accommodation (NRA), positive relative accommodation (PRA), near and distance horizontal dissociated phorias, near and distance negative and positive fusional vergence, and near point of convergence (NPC)). Both monocular as well as binocular accommodative responses were measured by two different methods: monocular estimate method (MEM) retinoscopy and the cross-cylinder subjective method. Then the data were analysed by the statistical package SPSS18.0to determine the differences of these parameters when myopes was corrected with either spectacles or SCL.ResultsAll subjects (N=30) completed the study. The spherical equivalent of their refractive errors were between-0.75D and-6.50D, with a mean value of-3.48±1.40D. The monocular accommodation amplitude measured by minus lenses method was significantly lower with the use of SCL in comparison to spectacles (P<0.01). The monocular and binocular accommodative lags measured by two different methods (MEM and cross cylinder methods) were both lower with the use of SCL in comparison to spectacles (P<0.05). Significantly higher NRA was found with the use of SCL in comparison to spectacles (P<0.01). The near horizontal dissociated phorias measured by von Grafe method was significantly lower with the use of SCL in comparison to spectacles (P<0.01). The near negative fusional vergence was also significantly lower with the use of SCL in comparison to spectacles (P<0.01). The differences of other parameters measured when myopes was corrected with either spectacles or SCL were not statistically significant (P>0.05).Conclusions1. The finding of higher lag with SCL worn in this study might be particularly important in increasing the risk of myopia progression.2. The higher NRA value with the use of SCL in the present work could indicate that the two methods of refractive correction were not exactly equivalent in then-ability to relax accommodation or to exert positive and negative fusional vergence.3. Some other parameters measured in this work, such as accommodation amplitude and accommodative facility, although not statistically significant, were different when myopes was corrected with either spectacles or SCL, which should be paid more clinical attention and further study.