The Design and Testing of an Additive Manufacturing-Obtained Compliant Mechanism for the Complex Personalisation of Lenses in Clinical Optometry

Abstract

The precision needed in optometric measurements for the correct customization of progressive lenses usually falls short of what is required for accurate prescriptions. This usually stems from the fact that most measurements are obtained using outdated methods, employing either rulers or protractors. While there is equipment available for precise measurements, the cost of purchase and ownership is usually prohibitive. In this context, due to constant progress in high-resolution cameras along with the processing power of handheld devices, another solution has presented itself in different iterations in the past decade, as put forward by different manufacturers of optical lenses. Such a system comprises a mobile computing device with image capture and processing capabilities (tablet or smartphone), along with a marker support system to be mounted on the user’s glasses frames. Aside from cost, the ease of implementation and usage, the advantage of such a system is that the parameters, as measured, allow for better customization, since the eyewear is already in the position in which it will be used. It allows the optometrist to measure parameters such as interpupillary distance, pantoscopic angle and the curvature of the eyewear in relation to the user’s own specific shape and size. This paper proposes a model of a marker support system that is easy to use, precise, low in cost and has minimal impact on the measurements obtained by the optometrist. As such, this paper examines the steps for determining the shape needed for supports in relation to the measurements that need to be taken; a finite element analysis of the support was proposed, along with various tests and modifications that were made to the device until a specific shape and material combination was found that satisfied all of the parameters required. An experimental model of the system was produced and tested on a wide variety of glasses frames with good results, as presented in the following work.

Keywords

• compliant mechanism
• optometry
• progressive lens customisation
• additive manufacturing