How to Choose Prescription Swim Goggles
The selection of appropriate corrective lenses for the swimming goggles does require some understanding of your visual acuity requirements and your most recent prescription.
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 diopters 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 diopter lenses (which do not correct for cylinder) you must add one half (½) of this number (to a maximum of .50 diopter) to the sphere number to determine the correct step diopter 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!!
Then calculate manually by using the formula below to figure out your lens strengths.
SPH____ + 1/2 Cyl ____ = _____
Always move DOWN to the closest step diopter while you need to pick up one from available step diopter lenses. If calculation of your prescription shows that you should have a -3.75 (step diopter lens) then you should choose a -3.5 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.
Enjoy your swimming experiences with Dr. B.
Remarks: Please note that the goggle lenses are of step diopter construction. This means that they will not exactly match your prescription and are not meant for prolonged use. Dr.B Optical Goggles should not be used for diving or other high-impact water sports. Careless or inappropriate use can cause injury.