Prescription Goggles Help - How do I choose the proper strength lens?

Choosing the proper strength lens can seem a little confusing, which is why we have provided you with a quick and easy way to determine what lens strength is right for you.

First, it's important to note that our lenses are negative dioptre lenses for Myopic (nearsightedness) correction. We do not carry positive dioptre lenses at this time.

The selection of appropriate corrective lenses for the swimming goggles does require some understanding of your visual acuity requirements and your most recent prescription.

What do I need to do first?

Find out what your existing eyeglass prescription is! The person who tested your eyes or who dispensed your last pair of glasses will have this information and will give you the details. The prescription numbers will contain some uncommon terms, such as:

• OD - Ocular Dexter (simply means your RIGHT eye)
• OS - Ocular Sinister (your LEFT eye)
• Sphere - This measures the degree of weakness in dioptres and for nearsighted (myopic) people this is always a (-) negative number
• Cylinder - This refers to the degree of astigmatism in the eye. In selecting step dioptre lenses (which do not correct for cylinder) you must add one half (½) of this number (to a maximum of .75 diopter) to the sphere number to determine the correct step dioptre lens!

CAUTION: Ophthalmologists often use a + (positive) number for cylinder and you then have to be careful with the + and - signs when doing the calculations!!

How do I calculate my lens strength?

Determining your correct lens strength can be done easily by using the following formula.

	Sphere		Cylinder	Calculation
Right Eye (OD)	__________	+ (½ of	__________ )	= __________ right eye lens diopter strength
Left Eye (OS)	__________	+ (½ of	__________ )	= __________ left eye lens diopter strength

For example,

• If the sphere is -2.5 and the cylinder is -1, then -2.5 + (1/2 x -1) = -3 step dioptre lens
• If the sphere is -4.0 and the cylinder is +2, then -4.0 + (1/2 x +2] = -3 step dioptre lens

In both of the examples above, a -3 dioptre aquagoggle lens would be best.

In situations where the cylinder is 0, the same formula is still used.

For example,

• If the sphere is -2.5 and the cylinder is 0, then -2.5 + (1/2 x 0) = -2.5 step dioptre lens
• If the sphere is -4.0 and the cylinder is 0, then -4.0 + (1/2 x 0) = -4 step dioptre lens

See, simple! By plugging in the appropriate values into the formula above, you can determine what lens strength you need for your Aquagoggles prescription goggles!

Special Considerations

In order to produce lenses for swimming goggles, and keep the price reasonable they are made in one-half (.5) dioptre increments. These lenses are not a full custom prescription and do not correct for cylinder or astigmatism. They are not intended for full time wear. Extended wear of step dioptre lenses will cause various degrees of eye strain but they are more than adequate for occasional wear especially if the cylinder is close to or less than 1.

Always move DOWN to the closest step dioptre! If calculation of your prescription shows that you should have a -2.75 (step dioptre lens) then you should choose a -2.5 lens for the swimming goggles. This causes less strain and you will be unlikely to notice any significant loss of acuity within a reasonable distance. There is also a slight magnifying effect when underwater.

Getting used to Step Dioptre Lenses

The corrective lenses in these swimming goggles do not have correction for cylinder and are not a direct match for your regular prescription but are more than adequate for temporary use.

A number of swimmers have told us that it takes a short while to adjust to their goggles. Wear them for a few minutes, your eyes will adjust and you will be more than satisfied with the results! Enjoy your swimming experiences and please drop us an email with your comments.