Diopter should remain the same above and below water. Because water and air are different medium,only an absolutely flat lens can do it.

What is water optics?

Human being is a terrestrial animal. Human eyes are accustomed to such medium, air, index of refraction: 1.0 (see Figure 1). When we dive into the water (index of refraction: 1.33), eyeballs contact directly with water. Because the indexes of refraction for eyes and water are almost the same, any objects are barely focused. As a result, our vision is so impaired that we can not judge distance accurately (see Figure 2).

Vision varies above and below water as a result of lens curvature

We come out and in the water constantly to breathe, so our vision also continuously change (See Figure 1 and 2). Like we see things in a glass of water, we may find that it is constantly changing in different angles. The flatter the surface is,the clearer picture you will see.

Convex outer surface of swimming gogglesvaries vision

SABLE believes that anyone involves in water activities would need a pair of swimming goggles made in accordance with water optics whether his or her eyes are in healthy condition, nearsightedness, or farsightedness.Therefore, SABLE, long devotes to water optics, conducts these primary experiments to demonstrate the differences. which normal plastic glasses would show (see Figure 3and 4). Those plastic glasses are usually curved, uneven in terms of thickness, impurity resulting in confusion,astigmatism and irregular diopters.

Nowadays, manufacturers produce swimming goggles according to optics in normal condition. When used those goggles in the water, the optical power will increase 2.00 to 3.00 diopters (see Figure 3). Human optic nerve could not manage to adjust to such violent changes. People may feel tired or even dizzy in severe situation. Eyes could also be damaged permanently.

A lens with flat surface and concave inner wall does not distort light

SABLE has attended attentions to changes of lights in different medium ever since 1984 and has applied the flat convex principle to every single SABLE swimming goggles. As a result of such insist, SABLE is able to guarantee that the light move directly through goggles and the diopters remain unchanged (see Figure 4)