While scuba diving, many things affect your
vision. These changes in your vision occur mainly because light
travels differently under water than above water. This can make
our perception of things we see underwater slightly altered. Some
of these alterations in light rays are refraction, scatter, and
absorption. All of these conditions follow physical laws and their
effects on human vision can be predicted.
Refraction is when light rays travel from one medium to another medium of different density, and are bent. When this happens, the image that you are looking at between the air in your mask and the water is magnified. This causes whatever you are looking at to appear three-fourths of the distance away from you than it really is. When the object is further away, this change reverses itself, and the object that you are looking at seems to be further away than it actually is. The mediums of different densities, however, are not the only things that can cause refraction. If the water is murky, the certain distance at which the reverse refraction occurs becomes shorter. As a result, new divers that try to get hold of certain objects will find that they will have a difficult time.
Scatter occurs both above water and below water. However, the effects of scatter are much more severe under water. This is because the suspended water molecules scatter the light in all different directions. Not only water molecules cause scatter, but all suspended organisms of matter. This affects your vision and photography under water. This is because when the particles of matter scatter the light in different directions it reduces the amount of contrast between the object that you are looking at (or taking a picture of) and its background. Therefore, you cannot see as clearly underwater as above water.
Absorption is when the object you are looking at under water appears to be a different color than it really is. Absorption is caused mainly because as the light travels though the water, a large amount of it is absorbed and lost in the process. Unlike scatter, the clarity of the water does not affect how much the object you are looking at is changed.
In conclusion, all of these changes can affect your vision in many ways while you are scuba diving. Some of these affects include change of perception in the distance, size, and color (otherwise known as, refraction, scatter, and absorption) of the object that you are looking at.