## 1 Introduction  
The use of multiple types of measuring systems is widespread in the field of optometry, and specialists rely on such devices along with specific methods to determine a patient's specific needs in regard to customizing lenses. In this regard, certain aspects of measuring these parameters are perceived as being mandatory, such as determining the user's perceived effect of the lenses on vision in a real-world environment: reading a computer screen, a book, looking in the distance. One such aspect is that the glasses and lenses should be mounted on the patient's face, and their position should not be in any way modified by the measuring apparatus. This is especially true when it comes to personalised progressive lenses. As such, certain requirements have been identified, as explained below:High elasticity--the mount should allow for usage with a wide array of models of glasses. * Maximum weight 5 g--total weight of the system will be two such mechanisms, for a total of 10 g. It was considered that the mounting bracket should not be heavier than one of the lightest pairs of glasses. This is mostly an empirical parameter, based on previous iterations of such systems. * Good resistance to repeated usage--the system should not be prone to easily breaking while being used for multiple dimensions of seeing glasses. * Easy to manufacture, but especially easy to modify between product iterations due to the shifting fashions in eyewear; the mounting bracket should easily follow suit. * Low cost and good aesthetics
* Made in one part--measuring accuracy will greatly depend on how well the system is assembled. Related to this last point, a special model of a compliant mechanism that achieves the transmission of force and motion through its own elastic body transformation was proposed. Through several iterations, a shape was obtained, mostly being designed around the normal shape of a user's glasses frames. Figure 1 shows two views of the proposed mechanism (side and isometric view), which is equipped with two handles. A force of approximately 35 N (each) will be exerted on them, which is necessary to open the mechanism with a total stroke of 30 mm. The forces necessary to open the mechanism are determined following the study in the specialized literature [1], and of some simple tests performed in the laboratory--allowing an average user to open the device with minimal effort. Similar systems have been developed for use in the field of optometry. Such systems, currently employed throughout optometry clinics allow for easy measurement, with relatively low errors of a small number of parameters, such as interpupillary distance, total, left and right, as well as a basic calculation of the boxing parameters needed when cutting and fitting the lens to a specific frame. One such example is the VisionFit Dispensing System [2], which allows for measurement of interpupillary distances both for near and far, boxing measurements, as well as some fitting parameters of the frames. This system does not, however, allow for complex measurements to be taken (curvature of frames and pantoscopic angle). Another such system is the Optikam [3], which allows measurement of a much larger number of parameters, but does feature a very large and complex system for attaching the markers to the patient's face, and thus runs the risk of interfering with the natural position the frame would otherwise have on the patient's face. Another such system is the DigiFit, which allows for measurements of a large number of parameters, but does, however, generally require the lens to be taken out of the frame. Since some corrections, such as squinting, are made by the lens, a complex system must be employed to allow for corrections to the lens's optic centre [4]. While the systems presented thus far allow for some parameters to be measured, there are systems under use that allow for all parameters to be obtained. These, however, are  
Figure 1: General view of mechanism.