Accommodation is the process of adjusting focal distance to achieve a clear retinal vision by altering the shape of human crystalline lens in the eye. Accommodative responses are composed of two parts, phasic and tonic. The adequate phasic accommodation is needed to form a clear retinal image of near stimuli. The proper tonic accommodation is needed to maintain clear retinal vision after the initial phasic response. The phasic and tonic accommodative responses are mediated by the sympathetic and parasympathetic systems. Accommodative accuracy and endurance is achieved by modifying the neuromuscular connection through repetitive learning and adaptation.~Vision training has been shown effective to increase accommodative amplitude and endurance. Its efficacy is achieved by gradually increasing the difficulty of tasks that require patients to attentively process visual cues to adapt their accommodative responses. Its end goal is to induce effective and permanent adaptations to the visual environment. The process of vision training has been theorized as a bioengineering model in which the neuromuscular signal is altered through visuomotor feedback. The increase in accommodative accuracy is thought to reflect the gain of accommodative responses and the increase of accommodative endurance is the result of maintained tonic neural output.~Empirical studies have shown the Digitalisglycosides (DGS) can enhance muscular contraction and Esculin improves micro vascular circulation. Stulln eyedrops include these active ingredients and have been approved to treat visual discomfort and retinal macular diseases in Europe and China. It also has a very good safety record, without any report of adverse effects to human body for the millions of users each year. The efficacy of Stulln in treating visual discomfort might have resulted from the improved microcirculation of blood and wastes, leading to better ciliary functions. Indeed, empirical studies have shown Stulln application can improve accommodative amplitude, facility and endurance. However, Stullen itself might not produce long-term changes in neuromuscular innervation, as its ingredients can be removed from the human body within an day.~The present study tests the hypothesis that Stulln eyedrops improve accommodative functions by improving the short term accommodative facility and endurance. To test this, the investigators propose to conduct a prospective randomized control trials where participants with accommodative dysfunctions are randomly assigned to three groups: control, Stulln only and Stulln plus vision training. The investigators' theory predicts that the efficacy of Stulln will be augmented by vision training.
The present study tests the hypothesis that Stulln eyedrops improve accommodative functions by improving the short term facility of ciliary muscles that can be transferred into long-term adaptation. To test this, the investigators propose to conduct a prospective randomized control trials where participants with accommodative dysfunctions are randomly assigned to four groups: control, Stulln only and Stulln plus vision training. The investigators' theory predicts that the efficacy of Stulln will be augmented by vision training.