By law opticians are obliged to provide you with a prescription.  Once you have had a thorough eye test they must give you a copy of your prescription without requiring you to make a purchase. 

The type of information on your prescription, which is also the information we need you to enter when ordering your glasses comes in four main parts : ‘Sphere’, ‘Cylinder’ ‘Axis’ and “Add”

• Sphere (Sph) specifies the strength of the lens: plus (‘+’) for long sightedness, minus (‘-‘) for short sightedness.
• Cylinder (Cyl) is your astigmatism correction. If you don’t have a value for astigmatism, you can leave this blank.
• Axis is the angle that your astigmatism is set at. You don’t need to enter a value if you have not entered a value for Cylinder.
• Reading Addition (Add) is needed when you need glasses set for close work only, or if you need bifocals.