Sweetkermit:
CAAS sets the baseline safe standard which flight crew are required to meet on a 12-monthly basis (or 6-monthly basis as dependent on their age and/or type of operations) in order to maintain their Medical Certification.
The employer, on the other hand, has the prerogative to set their own baseline standard as they are the ones who will be sponsoring the cadet's entire training and thus it is only logical to have positive "return on investment".
How is this so?
In the medical field, an spherical equivalent of uncorrected visual acuity (UCVA) of more than -6.00 dioptres (commonly referred to as 600 degrees of myopia) is considered "High Myopia".
A simple google search will bring up various risks for those with "High Myopia".... such as: "holes or tears in the retina and can also cause retinal detachment. Abnormal blood vessels may grow under the retina and cause changes in vision" Please search for more information relating to "High Myopia" and "Astigmatism" if you're keen.
Hence, having moderate myopia is the maximum risk that the airline is willing to accept if they are going to spend about S$250k on your training.
If you're determined, the self-sponsored route is always open. In aviation, there will always be plenty of obstacles before one can reach his/her final goal. It's a test of one's determination and endurance.