Q: Is LensWebShop extension pre-loaded with prescription values ?
A: No, this extension is not pre-loaded with prescription values because each shop may have different values. However, features have been provided to make importing easy, please check the below link for screen-shots of the same.
http://www.magentocommerce.com/magento-connect/medma-lenswebshop.html
Q: Is each product with let’s say 100 different prescription powers / variants automatically shown as 100 SKUs in the database?
A: Yes, each prescription value is added as a product so 100 different prescription powers are shown as 100 SKU.