# The Montreal Experience: A Retrospective Study Part I--Basic Principles and Treatment Algorithm
## 4 Discussion
The second pillar relates to the binocular vision management. Every patient showing significant BV dysfunction is referred to the BV clinic, at the Universite de Montreal, prior to myopia management. On average, this represents 10 to 15% of the patients seen, which is comparable to the prevalence in a general population [40]. BV management occurs prior to implementing myopia control strategies. This means that all of the participants in this study were considered to have normal BV function at baseline. This represents one reason why it was not possible to isolate BV function as a factor in our analysis. The third pillar relates to the control of the blur, centrally and peripherally. Central vision plays a minor role in myopia management but it still important to consider, knowing that under-correction leads to myopia progression. Participants were seen at 6-month intervals, following the recommended schedule of visits at CUV clinic. This does not mean that all of the participants enrolled at baseline were seen precisely every 6 months. Some follow-up visits may had been delayed due to agenda issues, compliance, availability, etc. Control of the central blur means that full correction of myopia is prescribed and adjustments are made whenever necessary. Control of the peripheral blur is based on the presence of a dose-response effect in the system. To maximize the dose, we aim to generate the highest convex power possible (high add or customized peripheral ring power for OK lenses) and the relationship between the central and peripheral zones is calibrated based on the pupil area. This will be detailed in a future article (Part 2). Consequently, it is not only the level of the convex power that matters, but also its distribution in front of the visual system. Because OrthoK lenses 2, 3 and 4 adopted smaller treatment zones, and they are then providing a higher dosage, it was expected the lenses would achieve a better outcome. This is confirmed by the overall results presented here: smaller treatment zone designs were more effective than the larger ones (see Table 8). Soft multifocal lenses are preferred habitually (see Figure 1b) when myopia is lower but more when the pupil area is limited. As mentioned, it may be difficult to design a customized OK lens with a very small central treatment zone without impacting its overall behavior. It is then associated with a loss of suction effect and consequently lower convex power is generated. Our results do not support this theoretical approach and may express the personal preference of CUV experts. In fact, there was little observed difference in the average refractive error and pupil diameter between our groups. We found that SMCL provided similar control when compared to the OrthoK 1 lens, and, with no surprise, was less effective than other OK designs (Table 8). This is true for the first and the second year of treatment. Detailed analysis about SMCL performance will be given in another manuscript (Part 2). Low-dose atropine treatment was the least effective among the strategies prescribed to this cohort of participants. (See Figure 2). The difference with OrthoK 1 or SMCL is not statistically significant but, again here, OrthoK 2-3-4 were significantly more effective than LDA. What is concerning is the fact that participants treated with LDA as a standalone therapy were not so well controlled versus the theoretical control. This may be explained by the fact that, in 2017, a concentration of 0.01% was prescribed, as it was standard practice around the world. This is highlighted in the first year of the treatment. Later on, higher concentrations were used (0.025%) in light of more recent data [41] reporting the reduced efficacy of the smallest dosage of atropine on AL elongation. This increased dosage seemed to be more effective based on the results obtained during the second year. In the practice of the Montreal Experience, it is not common that atropine is used as a standalone therapy.