The Object Constraint Language (OCL) is a OMG standard that plays an important role in the elaboration of precise models. However, it is not hard to find models and metamodels containing overly complex OCL expressions. Refactoring is a technique that can be used in this context since its goal is to reduce complexity by incrementally improving the internal software quality. Indeed several refactorings have already been proposed to improve the quality of OCL expressions. This paper presents the results of an empirical study that investigates the impact of poor OCL constructs, also known as OCL Smells, and OCL refactoringson the understandability of OCL expressions. Current results show that most refactorings significantly improve the understandability of OCL specifications.