Typhoon Exel Mask
***** PRESCRIPTION lens mask *****
Description:
A low volume, twin lens silicone mask which can be fitted with optical lenses (supplied separately).
Fabrics:
- Silicone (skirt)
- Plastic (frame)
- Tempered glass (lens)
Qualities:
- Comfortable and supple (silicone)
- Twin lens
- Option for optical lens fitting
- Standard mask £19.99
- With 1 PRESCRIPTION lens £39.98
- With 2 PRESCRIPTION lens £59.97
Prescription lens from -1 to -6.5 Diopter (in 0.5 increments)
Colours: yellow or blue
Helpful info
(Please note I am NOT an Optician, but I understand the information below my help you make the right decision on what lenses suit you):
Choosing the proper strength of lens
Our lens are all Negative – dioptre and for Myopic correction!
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 Step: 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:
Terms:
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 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!!
Examples Sphere is -2.5 and cylinder is -1, [-2.5 + 1/2 of -1] = -3 step dioptre lens
Sphere is -4.0 and cylinder is +2, [-4.0 + 1/2 of +2] = -3 step dioptre lens
In both of these examples a -3 dioptre lens would be best.
Examples if you have "0" cylinder
Sphere is -2.5 and cylinder is 0, [-2.5 + 1/2 of 0] = -2.5 step dioptre lens
Sphere is -4.0 and cylinder is 0, [-4.0 + 1/2 of 0] = -4 step dioptre lens.
Special Considerations: 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.
Step Dioptre Lens - 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.
Currently no -2.5 L lenses available
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