This should be under pre-optometry, I believe.
Optomcas does have it's own specific method for gpa calculation; however the individual schools do not all use this method. For example, I applied to ICO and had to manually submit to them a pre-req. and gpa calculation sheet that was separate (and slightly differently calculated) from optomcas (hence they have their own gpa calculating system); I can also say that I did not have to do this for either Salus or SUNY. I'd definitely call the admissions offices of schools for any specific questions you might have pertaining to your application.