How to choose the correct mask size

Q: What is the difference between nearsighted and farsighted lenses?

Nearsighted (myopia) lenses use negative SPH values to correct distance vision. Farsighted (hyperopia) lenses use positive SPH values to help with close-up vision.

Q: How do I find the sphere (SPH) value on my prescription?

Look for SPH or Sphere. It can also be labelled Power or PWR. A minus sign (-) is nearsighted and a plus sign (+) is farsighted.

Q: How should I adjust my prescription for clear vision underwater?

For most people, choose 0.50 diopters weaker (towards zero) than your normal SPH, then select the closest available 0.50 step.

Q: I have astigmatism (CYL). What should I choose?

Use your SPH for each eye. The + or minus sign on your CYL matters. Nearsighted: CYL 0.00 to 0.75 go 0.50 weaker. CYL 1.00 to 1.75 minus CYL stay close to SPH up to 0.50 either direction. CYL 1.00 to 1.75 plus CYL stay at SPH or 0.50 weaker. CYL 2.00+ minus CYL stay at SPH. CYL 2.00+ plus CYL stay at SPH. CYL 3.25+ nudges toward SE. Farsighted lenses come in whole steps +1 to +5. Special case: SPH -0.50 or -0.75 with CYL 2.50+ start at -1.00. SPH +0.50 or +0.75 start at +1.00.

Q: I can't find my lens strength in the dropdown. What should I do?

Choose the closest available option. Upload your prescription or email info@oceansoptics.com if you want us to confirm the best match.

Q: How do I stop my mask from fogging?

Try the toothpaste trick: rub a small amount on the inside of each lens in circular motions, then rinse. Before each session use a tiny amount of baby shampoo or dish soap, rub a thin film on the lens, then lightly rinse.

Q: Do you have a guide to help me use my mask properly?

Yes. Mask 101 guide: https://cdn.shopify.com/s/files/1/0798/8055/2781/files/Mask_101.pdf?v=1728895468

Navigating Clarity: A Guide to Choosing Myopia ...

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Navigating Clarity: A Guide to Choosing Myopia Lenses for Your Diving Mask Embarking on an underwater adventure is a thrilling experience, and for those with myopia, ensuring crystal-clear vision...

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Navigating Clarity: A Guide to Choosing Myopia Lenses for Your Diving Mask Embarking on an underwater adventure is a thrilling experience, and for those with myopia, ensuring crystal-clear vision...

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Frequently Asked Questions

What is the difference between nearsighted and farsighted lenses?

Nearsighted (Myopia) lenses: Negative SPH values (example: -2.50) to help you see clearly at distance.

Farsighted (Hyperopia) lenses: Positive SPH values (example: +2.50) to help with close-up vision.

How do I find the sphere (SPH) value on my prescription?

Look for the column labelled SPH or Sphere. It can also be labelled Power or PWR. A minus sign (-) is nearsighted. A plus sign (+) is farsighted.

How should I adjust my prescription for clear vision underwater?

Underwater adjustment: For most people, choosing a lens that is 0.50 diopters weaker (towards zero) than your normal SPH gives the best comfort and clarity underwater.

Why: Water creates natural magnification, and mask lenses sit further from your eyes than glasses. Reducing by 0.50 helps keep vision feeling natural and comfortable underwater.

Examples: If your SPH is -2.25, choose -2.00. If your SPH is -2.75, choose -2.50.

Our lenses are available in 0.50 increments, so choose the closest available option.

I have astigmatism (CYL). What should I choose?

Our lenses are sphere only, meaning they correct SPH but not CYL directly. You can still see a significant improvement. Use your SPH for each eye, then adjust based on your CYL value and sign.

Important: The + or − sign on your CYL matters. Check your prescription slip for the sign next to your CYL value.

Nearsighted (Minus −) lenses

CYL 0.00 to 0.75: Go 0.50 weaker than your SPH (closer to zero). The CYL sign has little impact at this level.
CYL 1.00 to 1.75 with minus CYL (−): Stay close to your SPH. You can go up to 0.50 stronger (further from zero) or up to 0.50 weaker (closer to zero).
CYL 1.00 to 1.75 with plus CYL (+): Stay close to your SPH. You can go up to 0.50 weaker (closer to zero) or stay at SPH.
CYL 2.00 to 3.00 with minus CYL (−): Stay exactly at your SPH. Only go 0.50 stronger if you specifically want sharper detail.
CYL 2.00 to 3.00 with plus CYL (+): Stay exactly at your SPH. Do not go weaker.
CYL 3.25+ with minus CYL (−): Move slightly toward stronger correction, rounded to the nearest 0.50 step.
CYL 3.25+ with plus CYL (+): Move slightly toward weaker correction, rounded to the nearest 0.50 step.

Special case: If your SPH is −0.50 or −0.75 and CYL is 2.50 or higher, start at −1.00.

Farsighted (Plus +) lenses

Our farsighted lenses come in whole steps only: +1.00, +2.00, +3.00, +4.00, +5.00.

CYL 0.00 to 0.75: Round to the nearest whole number toward zero.
CYL 1.00 to 1.75 with minus CYL (−): Round to nearest whole number, or one step stronger for sharper detail.
CYL 1.00 to 1.75 with plus CYL (+): Round down to the nearest whole number.
CYL 2.00 to 3.00: Stay at your SPH rounded to the nearest whole number.
CYL 3.25+ with minus CYL (−): Move toward stronger correction, round to nearest whole number.
CYL 3.25+ with plus CYL (+): Move toward weaker correction, round to nearest whole number.

Special case: If your SPH is +0.50 or +0.75, start at +1.00 regardless of CYL.

Use our Underwater Lens Calculator for an instant recommendation, or see our full guide: Choosing prescription snorkel mask lenses with astigmatism.

If you are unsure, upload your prescription and we will check your selection for you.

I can't find my lens strength in the dropdown. What should I do?

The dropdown shows all strengths available for that specific mask. If your exact number is not listed, choose the closest available option using the guidance above.

If you want us to confirm the best match, upload your prescription on the product page or email us at info@oceansoptics.com.

Can I choose different lens strengths for each eye?

Yes. You can select different strengths for left and right eye. You can mix and match any combination available in the dropdown menu.

How do I upload my prescription during checkout?

On the product page you can optionally upload your prescription so we can check your selection before we build it. You can also leave a note in the cart, or email us at info@oceansoptics.com.

How do I stop my mask from fogging?

A simple method is the toothpaste trick. Rub a small amount of toothpaste on the inside of each lens using circular motions for a few minutes, then rinse thoroughly. Do this before your first use and repeat if needed.

Before each session, you can also use a tiny amount of baby shampoo or dish soap mixed with water. Rub a thin film on the inside of the lens, then lightly rinse so a fine layer remains.

Do you have a guide to help me use my mask properly?

Yes. Here is our Mask 101 guide: Open Mask 101 (PDF).

What happens if I accidentally choose the wrong lens strength?

Message us as soon as possible. If the order has not entered the build or shipping stage yet, we can usually update the lens selection.

Are your lenses safe for both snorkeling and scuba diving?

Yes. Our lenses are HD tempered glass and are suitable for snorkeling and scuba diving up to 100 ft (30 m).

How long does delivery take, and can I track my order?

Most orders arrive in 5 to 10 days, but we recommend allowing up to 14 days to be safe. You will receive a tracking number by email once your order ships.

What is your return or exchange policy for prescription masks?

Your satisfaction, guaranteed.
You have 30 days from delivery to request a return, as long as the item is unworn, unused, with tags, and in original packaging. For full details, visit our Return Policy.

How to choose the correct mask size

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Frequently Asked Questions