## 2 Materials and Methods
### Orthokeratology Lens Designs  
Over the years, 4 different designs of OK or C-OK (customized orthokeratology) lenses were prescribed. Lens parameters are shown in Table 1. At first, the lens selected was based on availability and clinician's preference, and in late 2017 to early 2018, most lenses were customized by software (RGP Designer, Italy, version 1.0). OK lenses differ in design, some of which were originally developed for myopia correction (OK 1 and OK 4), while the other two have designs that have been adapted for myopia management by allowing for more customization (OK 2 and OK 3). The OK 1 used in this study had a spherical base curve (BC) with a standard BOZD of 6 mm. The proprietary \"sigmoid proximity\" (inverted) curve is a third-order polynomial that connects the base curve to the tangential peripheral curve. The standard overall diameter is 10.5 mm and the lenses are made of Hexafocon A with a Dk of 100 [23]. At the time of the study, peripheral toric curves and/or smaller central zones were not available. The design of the OK 2 lens was customized using a software developed for this purpose. This allowed the authors to create a lens template in which all parameters could be modified to suit the patient's characteristics. Specifically, the lens is designed with seven curves, and the diameter of the posterior optic zone is selected according to the \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Lens Type** & **Brand Name** & **Material** & **Number of Curves** & **Back Optic Zone** & **Jessen Factor** & **Lens Power** & **Overall Diameter** \\  & & & **Curves** & **Diameter (mm)** & **(D)** & **(D)** & **(mm)** \\ \hline OK 1 (OK) & \begin{tabular}{c} Paragon CRT \\ (Cooper Vision, San Ramon, CA, USA) \\ \end{tabular} & Hexafocon A & Four & 6.0 & 0.50 & +0.50 & 10.5 \\ \hline OK 2 (C-OK) & \begin{tabular}{c} Université de \\ Montreal design \\ (custom; RGP \\ designer software) \\ \end{tabular} & Hexafocon A & Six & \begin{tabular}{c} Variable: \\ Between 5.4 and 6.0 \\ Mean = 5.6 \\ \end{tabular} & \begin{tabular}{c} Variable. \\ Mean = 0.75 \\ \end{tabular} & \begin{tabular}{c} Variable. \\ Mean = +0.75 \\ \end{tabular} & \begin{tabular}{c} Variable. \\ Mean = 10.6 \\ \end{tabular} \\ \hline OK 3 (C-OK) & DRL (Pecelens, Cretel, France) & Hexafocon A & Five & \begin{tabular}{c} Variable: \\ Between 5.0 and 6.0 \\ Mean = 5.5 \\ \end{tabular} & 1.5 & +0.75 & \begin{tabular}{c} Variable. \\ Mean = 10.8 \\ \end{tabular} \\ \hline OK 4 (OK) & \begin{tabular}{c} DreamLens (Bauch \\ (N = 22) \\ \end{tabular} & \
\begin{tabular}{c} Hexafocon A \\ \end{tabular} & Five &
\begin{tabular}{c} 5.0 to 6.2 \\ Mean = 5.0 \\ \end{tabular} & 0.75 & +0.75 & 10.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Orthokeratology lens specs (OK: Orthokeratology, C-OK: Customized orthokeratology). pupil size. The reservoir is designed to achieve a minimum of 75 \(\upmu\)m and a maximum of 100 \(\upmu\)m, regardless of the myopic correction. Thus, it always produces a high level of defocus. Peripheral curves are designed to be toric if the difference in elevation between the two principal meridians along the 8 mm ring was above 20 \(\upmu\)m. The lens diameter is determined to cover 95% of the corneal surface, and the curve width is balanced accordingly. If necessary, the sagittal depth of the lens is adjusted with landing zone curves. The OK 3 design is also customized according to the manufacturer's protocol, which takes into account topographic keratometry values, refraction, and corneal diameter. This unique design includes a second tear reservoir that is formed at mid-distance between the reservoir and the lens edge, by a flattened curve coupled with a steepened curve. This second tear reservoir increases hydrodynamic suction forces, resulting in improved centration and faster epithelial changes. All lens fits were optimized until centration and correct refractive results were achieved.