How to Determine the Diopter for a Scuba Mask

How to Determine the Diopter for a Scuba Mask
Most scuba enthusiasts know how important their dive mask is. If you're a diver who wears glasses, you can purchase lenses for your scuba mask. Since they are cheaper, most recreational divers go for a step diopter dive mask lenses, also known as stock prescriptions lenses, rather than custom-ground lenses. Here is what you'll need to ensure you can see clearly during your next dive.


Difficulty: Moderately Easy

Determining Scuba Mask Diopters

Things You’ll Need:
  • Eye glass prescription Scuba mask
  • Eye glass prescription
  • Scuba mask
Step 1
Refer to your eyeglass prescription. Make sure the prescription has not expired. Decoding the prescription is not as difficult as it might seem. "Oculus dexter" (OD), "oculus sinister" (OS) and "oculus utrique" (OU) are Latin terms that mean right eye, left eye and both eyes. Sphere is the amount of correction needed in each eye. Cylinder is the amount of astigmatism.
Step 2
Locate both the cylinder and sphere number for the OD and OS. Don't be alarmed if the numbers are different for each eye.
Step 3
Choose the numbers for one eye. Then calculate the diopter. To do this, add the sphere number and half of the cylinder number. For example, a prescription that indicates a sphere of 2.0 and a cylinder of -.50 would be calculated as 2.0-.25 = 1.75.
Step 4
Round down when possible since water is a natural magnifier. Diopters are in increments of .25, so a diopter of 1.5 would be chosen.
Step 5
Repeat the same formula for the diopter of the other eye.
Step 6
Purchase specific diopters for each of the lens in your mask. You will find most dive shops have step diopter lenses in stock, and they will be able to replace regular lenses with them. You shouldn't have to show your prescription to purchase step diopter lenses. Dive shop professionals will be able to check your prescription to make sure you purchase the correct lens for your sight.

Article Written By Krista Raye

Krista Raye is a Steel Magnolia who began writing professionally in 2009 with eHow, Answerbag and Trails. She has 10 years teaching experience in middle and high schools. Raye holds a Bachelor of Arts in English, a Bachelor of Science in secondary English education and a Master of Arts in adolescent English education.

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