How to convert my glasses prescription into a contact lens prescription?

My glasses prescription is as follows:

Right: -6.50
Left: -4.50

Right: -0.50
Left: -1.00

Right: 175
Left: 165

I've been told that contact lens prescription usually need to be 0.5 - 1 lower in strength?

Thanks for your help

Getting contact lenses isn't just a simple conversion, it would be best to visit your optometrist and get the proper prescription for contact lenses, especially when it comes to astigmatism.

I tried once before to convert my prescription, but there is another dimension needed, but i cant remember what it is and cant find my prescription to figure it out, sorry
i think its an eye test only that will give you the correct prescription
but if you do get contacts look around on the www for cheap lenses i get mine far mor cheaped than the high street shops:)

The relationship between an eyeglass prescription and a contact lens prescription is related to the fact that eyeglasses are worn some mm in front of the eye, whilst the contact lens prescription is worn on the eye itself. Thus after being bent by the glasses prescription lenses the light continues to travel through the air for another 12-14mm before entering the eye, whilst the contact lens bends the light immediately before it enters the eye. The distance which the bent light travels before it enters the eye is called the Back Vertex Distance (BVD) and a usual value for this is 12-14mm. This value should be written on your prescription if it is greater than +4.00 or -4.00.

A complicated formula can be used to calculate a likely contact lens prescription from a spectacle prescription, but it doesn't always work out. So you can't really be sure the prescription will be exact without using a trial lens and doing an over-refraction to measure any residual prescription.

Plus it's not just the prescription that describes the specification of the contact lens, because other factors such as the radius of curvature and diameter of your cornea need to be taken into account to ensure the lenses fit properly. Plus there is a moderate astigmatism in your prescription so you might need toric contact lenses to achieve really sharp vision.

You should visit an eye doctor for a contact lens fitting.

Ian Kenny