# Contact Lens-Based Microchannel Rings for Detecting Ocular Hypertension
## 2 Materials and Methods  
Daily disposal contact lenses (ACUVUE TrueEye) were purchased from Johnson & Johnson, Jacksonville, FL, USA. All lenses have a base curve of 9.0 mm and a diameter of 14.2 mm. The lenses were taken from their original packaging and stored in 46% H\({}_{2}\)O in buffered saline with methyl ether cellulose. Micro-channel rings were engraved on contact lens surfaces using a Rayject CO\({}_{2}\) laser (Mississauga, ON, Canada). The laser beam had a wavelength of 10.6 \(\upmu\)m, a variable output power with a maximum of 80 W, and a diameter of 20 \(\upmu\)m. The ablation process was carried out on the outer edges of the lenses to avoid vision obstruction during wear. The distance between the contact lens and the outlet of the laser beam was kept constant at 50 mm throughout all processes. Other parameters such as laser power and the scanning speed were validated and optimised using Rayjet software to avoid damaging the contact lenses. A schematic illustrating the laser system and the fabrication process is shown in Figure 1A. Two circular channels (rings) were created on the surface of the contact lens at different laser operation settings (power and scanning speed) to identify the optimum conditions. The geometry of the micro-channels and the processed contact lens are displayed in Figure 1B,C. An optical microscopic (ZEISS, Jena, Germany, Zen software: Saint-Louis, MO, USA) was used to image the modified surface of the laser-treated lenses. The performance of the contact lens was determined by measuring the change in the interspace for the ring-couple upon exposing the lens to different surface curvatures, corresponding to ocular pressure variations in the range 12-22 mmHg. The measurements were performed using an automatic calliper and a microscope (Figure 2A). The interspace between the laser-engraved rings was measured in flat and curved conditions for both the inner side and outer side of the lenses. Firstly, measurements were performed when the lens was fixed on a flat plastic sheet. Secondly, measurements were recorded when a force was applied on the sides of the plastic sheet to bend the lens, and the distance between the top of the lens and its bottom edge was 7.7 mm, which is the typical cornea radius of curvature. Furthermore, measurements were taken at a curvature of 15 mm, which represents the extreme risk of the cornea for developing glaucoma [2]. The distance between the two rings was measured by using the microscope's built-in software (Zen Software: Saint-Louis, MO, USA). Figure 1: Fabrication of concentric rings on contact lenses. (**A**) Schematic of the laser setup; (**B**) Illustration of the top and side views of the contact lens after the laser-treatment; (**C**) Geometrical features of the couple-rings with an interspace of 2 mm (for the couple-ring of diameters 8 and 12 mm), 1.5 mm (for the couple-ring of diameters 9 and 12 mm), and 1 mm (for the couple-ring of diameters 10 and 12 mm), and a photograph of the processed contact lens, scale bar 3 mm. Figure 2: Experimental setup to apply different curvatures to the contact lens and record the corresponding variations in the ring interspace. (**A**) Microscope stages: flat, curved at 7.7 mm, curved at 15 mm; (**B**) the balloon method: illustration for effect of the internal pressure on the surface curvature of the balloon. Another test was carried out to check the performance of the lenses. The contact lenses were fixed directly on a balloon surface to examine the effect of increasing the balloon's internal pressure and the balloon surface curvature on the interspace of the ring-couples, which was measured by a calliper and a smartphone (Figure 2B). The photos of the tested lenses were captured by a smartphone camera, and then ImageJ software was used to analyse the images measuring the interspace changes. The usage of a balloon assisted in simulating the change of the curvature for the eye cornea resulting from increasing of the IOP. The curvature of the balloon surface changed with the internal pressure of the balloon.