Measurement of the Optical Quality of Contact Lens Materials with Dehydration Significance

Abstract

Measurement of the optical quality of contact lens materials with dehydration significance An objective means for measuring the optical performance of different contact lens materials while dehydrating provides insights into their on-eye performance and comfort in cases of insufficient tear film stability. PURPOSE Different contact lens materials have different dehydration characteristics, particularly on the surface. Extended exposure to the ambient air may lead to a breakup of lens surface moisture. Furthermore, this breakup will lead to a degradation of the optical quality of the lens due to the irregularity of surface moisture and scatter from the surface roughness of the underlying bulk material. The purpose of this investigation is to objectively measure the optical quality through contact lenses during the dehydration process. METHODS An achromatic doublet with one surface having a radius of curvature like that of the cornea is mounted in a 3D printed “sclera” to provide a smooth transition between the lens and sclera. This artificial eye enables contact lenses to be placed onto its surface. A camera is then used to view a letter chart or distant point source at optical infinity through the eye model assembly. For measurement, a contact lens blister pack is opened. The lens is removed, and a drop of the packaging fluid is placed onto the back surface of the lens. The lens is then placed on the eye model and aligned to ensure good centration concerning the cornea and that no air bubbles are present underneath the contact lens. The second drop of packaging fluid is then placed on the anterior surface of the contact and a two-minute video clip of the eye chart viewed through the system is recorded. Letter visibility and contrast over time are assessed to determine the optical performance with time. RESULTS Two distinct progressions of the optical quality exist that are dependent upon the contact lens material. The first type of progression has the letter targets steadily blur and lose contrast. The optical quality will ultimately reach a minimum and then begin to improve to varying degrees. This effect is interpreted as the underlying contact lens surface being smooth and image quality is restored once the lens surface moisture has fully evaporated. Conversely, the second type of progression has the letter targets blur and lose contrast and then remain in that state. This is interpreted as the underlying contact lens surface being rough once the lens surface moisture is fully evaporated. The rates of degradation are also strongly contact lens material dependent. Introduction Different contact lens materials have different dehydration characteristics, particularly on the surface. Extended exposure to the ambient air may lead to a breakup of lens surface moisture. Furthermore, this breakup will lead to a degradation of the optical quality of the lens due to the irregularity of surface moisture and scatter from the surface roughness of the underlying bulk material. In this investigation, a system has been developed which enables a direct measure of the Point Spread Function (PSF), as well as tear-film break up on the anterior surface of the contact lens. In the first chapter, explains background on how the eye works, introduction to the components of the eye, its refractive errors, and correction of this refractive error with lenses is discussed. Chapter 2 focuses on the different types of contact lenses (based on materials) and problems for contact lens users can have after wear contact lenses. In Chapter 3 contact lens dehydration effects that cause degradation of image quality for contact lens users is explored. Chapter 4 talks about the design of an optical setup and analysis of the measured dehydration characteristics of different contact lens. Chapter 5 covers the measurement and analysis of the collected data. Chapter 6 will compare degradation data for different contact lens samples, and finally, conclusions and futures works will be discussed in chapter 7.