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 cannot 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 goggles varies vision
SABLE believes that anyone involves in water activities would need a pair of swimming goggles made in accordance to 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 3 and 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 flatconvex 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).

Normal goggles do not conform to the water optics
Normal swimming goggles use the plastic lenses, which do not conform to the water optics theory. Due to the lens surface is not flat, the scattering of light might arise and cause astigmatism. If the surface is convex, then nearsighted might arise. Normal prescription swimming goggles was made by convex and concave lens, if you wear this kind of goggles, the strength of goggles will have big difference above and below water. When swimming, your eyes are up and below the water, if the strength in the air is -3.0, it will become -5.0 in the water or even 500 astigmatism, how can your eyes coordinate this? You will feel dizzy、tired、un-comfortable and do not feel like swimming any more. The worst case is that you might throw up and in shock. It may also do harm to your eyes permanently.
To prove this theory, we conducted the following experiment. We used three stirs in three glasses with different curvatures. The shape of these stirs were changed due to different curvatures of the glasses below the water. This simple experiment proves that the stir in the rectangular glass changes the least. Likewise, the flatter the swimming goggles lens, the less distortion there will be and the better vision it can be.

A. The stir in the air.	B. A rectangular glass.The stir is slightly distorted.	C.A large round glass The stir is very distorted below water.	D.A small round glass with big Curvature.The stir is extremely Distorted.