# The Montreal Experience: A Retrospective Study Part I--Basic Principles and Treatment Algorithm
## 4 Discussion  
This retrospective study aimed to explore if the Montreal Experience approach is working in slowing myopia evolution over time. Results proved that it is, at least if we compare the cumulative progression against theoretical models for control. These good results were obtained regardless of the modality prescribed to the patients with the exception of low-dose atropine, especially during the first year of treatment. As expected, control efficacy during the second year is slightly less effective than during the first year of treatment [39]. Overall, the results indicate a cumulative axial length growth of 0.249 to 0.376 mm over 2 years, which is similar to the natural evolution of an emmetropic child of a matching cohort age. Considering OrthoK lenses (#2-3-4), the 2 years outcome matches a single year of evolution for control. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Change (mm)** & **OrthoK 1** & **OrthoK 2-3-4** & **SMCL** & **Atropine** & **Virtual Control** \\ \hline
1 year & 0.175 [0.128, 0.223] & 0.102 [0.066, 0.139] & 0.176 [0.143, 0.209] & 0.197 [0.144, 0.251] & 0.250 \\ \hline
2 year & 0.359 [0.289, 0.430] & 0.249 [0.193, 0.306] & 0.358 [0.305, 0.410] & 0.376 [0.290, 0.461] & 0.500 \\ \hline \hline \end{tabular} All data are associated with a \(p<0.01\) value. The \(p\) value is for a test of the hypothesis of no progression over the time interval. Virtual control values come from SCORM and OSLM studies.  
\end{table} 
Table 7: Model estimated first and second year average AL progression (with 95% confidence interval) by modality. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Time Interval** & **Modality 1** & **Modality 2** &
\begin{tabular}{c} **Mean Difference** \\ **[95\% CI]** \\ \end{tabular} & \(p\) **Value** \\ \hline One year change & Ortho K 1 & Atropine & \(-0.022\) [\(-0.094,\,0.050\)] & 0.543 \\ \hline One year change & Ortho K 2,3,4 & Atropine & \(-0.095\) [\(-0.161,\,-0.029\)] & 0.005 \\ \hline One year change & SMCL & Atropine & \(-0.022\) [\(-0.086,\,0.043\)] & 0.505 \\ \hline One year change & Ortho K 2,3,4 & Ortho K 1 & \(-0.073\) [\(-0.133,\,-0.013\)] & 0.017 \\ \hline One year change & SMCL & OrthoK 1 & 0.023 [\(-0.057,\,0.058\)] & 0.988 \\ \hline One year change & SMCL & Ortho K 2,3,4 & 0.073 [0.025, 0.122] & 0.003 \\ \hline Two years change & OrthoK 1 & Atropine & \(-0.016\) [\(-0.128,\,0.095\)] & 0.776 \\ \hline Two years change & Ortho K 2,3,4 & Atropine & \(-0.126\) [\(-0.230,\,-0.022\)] & 0.018 \\ \hline Two years change & SMCL & Atropine & \(-0.018\) [\(-0.121,\,0.085\)] & 0.730 \\ \hline Two years change & Ortho K 2,3,4 & Ortho K 1 & \(-0.11\) [\(-0.203,\,-0.021\)] & 0.017 \\ \hline Two years change & SMCL & Ortho K 1 & \(-0.002\) [\(-0.093,\,0.086\)] & 0.967 \\ \hline Two years change & SMCL & Ortho K 2,3,4 & 0.108 [0.032, 0.184] & 0.005 \\ \hline \hline \end{tabular} Model estimated mean differences between modalities in first- and second-year AL progression. For the difference estimate, Modality 2 change is subtracted from Modality 1 change. The \(p\) value is for a test of the hypothesis of no difference between the modalities in average progression over the time interval. \(p\) value adjusted for multiple comparisons.  
\end{table} 
Table 8: Comparative efficacy of modalities used to manage axial length at 1 and 2 years. The Montreal Experience is based on three pillars. This study was not powered to isolate the efficacy of each of these factors, but looked at them as an integrated approach. The first pillar relates to the control of the environment. At every visit, participants and parents are reminded of the importance of limiting screen time, to increase time spent outdoors, etc. However, it is not possible to certify that every child treated at CUV had been fully compliant regarding these issues. Data extracted from the files do not include questionnaires or objective measurements of these elements. On the other hand, this represents the real-life scenarios that many ECP are facing in their office on a day-to-day basis.