# Contact Lens-Based Microchannel Rings for Detecting Ocular Hypertension
## 3 Results and Discussion  
The CO2 laser parameters were optimized to yield microchannels with a depth of 20 \(\upmu\)m on surfaces of soft contact lenses. The laser power swung from 36 up to 48 W while the scanning speed was changed in the range of 440-520 mm\(\cdot\)s\({}^{-1}\). The distance between the laser outlet and the contact lens was kept fixed at 50 mm. Table 1 summarizes the laser system operation conditions and the geometry of the fabricated ring-couples on each contact lens. Microscope images of all laser-processed contact lenses are presented in Figure 3. The best results were achieved at the conditions of laser power 40 W and scanning speed 440 mm\(\cdot\)s\({}^{-1}\). Higher applied powers led cracks in the lens's surface, and lower input powers could not engrave convenient channels. The quality of the produced micro-channels was examined by the optical microscope. Three ring-couples with interspaces of 1, 1.5, and 2.0 mm, were engraved where the inner rings have diameters of 10, 9, and 8 mm, respectively, and the outer rings have diameters of 12 mm (Figure 4). An optical microscope was used to analyse the channels' depth obtained at optimum operation conditions of the laser system. To examine the performance of the processed contact lenses in determining the surface curvature, the lenses were fixed on plastic flexible sheets and the interspaces between the ring-couples were measured under the microscope (Figure 5A,B). The interspace measurements were repeated while the lens was curved at different radii of curvatures. Changing the curvature of the lens affected the interspacing between the engraved rings. The interspaces of the ring-couples in all examined lenses showed an increase with changing the lens conditions from flat to curved. Changing the conditions of the lens surface from flat to curved with a radius of curvature 7.7 mm led to increasing the interspace between the channels by up to \(\approx\)12%. For the lens having the ring-c couple of interspacing 1.5 mm, increasing the radius of curvature to 15 mm resulted in an increase in the interspace by \(\approx\)20% (Figure 5A,B). The interspace readings were recorded by examining either the engraved surface of the contact lens or the intact surface. Figure 5B illustrates that the readings taken \begin{table}
\begin{tabular}{c|c c c} \hline \hline \multirow{2}{*}{**TRIAL NUMBER**} & \multirow{2}{*}{
\begin{tabular}{c} **INTERSPACING** \\ **(mm)** \\ \end{tabular} } & \multirow{2}{*}{**LASER POWER (W)**} & \multicolumn{2}{c}{**SCANNING SPEED**} \\  & & & **(mm\(\cdot\)s\({}^{-1}\))** \\ \hline
1 & & 48 & 520 \\ \hline
2 & & 48 & 480 \\ \hline
3 & & 44 & 520 \\ \hline
4 & & 44 & 480 \\ \hline
5 & & 40 & 600 \\ \hline
6 & & 40 & 440 \\ \hline
7 & 1.5 & 40 & 440 \\ \hline
8 & 2 & 40 & 440 \\ \hline
9 & 2 & 36 & 440 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Contact lenses processed under different laser conditions to engrave the couple-rings. from the intact lens's surface are relatively similar to the results taken from the laser-treated side. The interspacing increased up to \(\approx\)10% and \(\approx\)20% at radii of curvatures 7.7 mm and 15 mm, respectively. The performances of the laser-treated lenses were confirmed by using the balloon method. The lens was fixed on a balloon surface and the interspace between the ring-couple was measured using a smartphone. This test was carried out at the normal IOP value, 12 mmHg, and in the glaucoma condition, 22 mmHg. It was found that the interspacing distance increases with pressure (Figure 5C,D). The interspace distance increased up to 4%, 10%, and 6% for the contact lenses having the ring-couples of interspacing distances 1, 1.5, and 2.0 mm, respectively, due to increasing the balloon internal pressure. To investigate the repeatability and signal drift for the developed sensor, its response for low and high pressure was recorded for four cycles (Figure 6A). The contact was attached to a balloon with internal pressures of 12 mmHg and 22 mmHg, and its interspace changes were measured.