underwater vision

• the eye is an organ that gives us the sense of light
• the eye is set in a protective cavity in the skull called the orbit, surrounded by fatty tissue
• the eye changes light rays into electrical signals and then sends them to the brain, which interprets these signals as visual images via the optic nerve
• cornea: the transparent part of the eye that covers the iris and the pupil and allows light to enter inside
• pupil: round opening in the center of the iris; makes the eye colour and can change size to let light into the eyes
• iris: coloured tissue at the front of the eye that contains the pupil in the center
• lens: a nearly transparent biconvex structure suspended behind the iris
• suspensory ligaments: a ligament suspending the lense
• aqueous humor: a clear fluid filling the space in the front of the eyeball between the lense and cornea
• vitreous humor: the transparent gelatinous tissue filling the eyeball behind the lense
• retina: a layer at the back of the eyeball that contains cells that are sensetive to light
• optic nerve: the second cranial nerve responsible for transmitting visual information
• refraction: the bending of light rays
• refractive index of water is about 1.33
• refractive index of the cornea is about 1.33
• when our eyes in water, instead of focusing images on the retina they now focus them far behind the retina, resulting in a blurred image from hypermetropia
• hypermetropia = long-sightedness
• the cornea, humours and crystalline lense of the eye together form a lens that focuses images on the retina
• having two eyes allows us to see depth
• by wearing a flat diving mask humans can see clearly underwater. The mask's flat window separates the eyes from the surrounding water by a layer of air.
• while wearing a mask objects appear roughly 33% bigger (34% in salt water) and about 25 times closer
• the orientation of the image formed on the retina is upside down
• a blind spot occurs in the eye because the spot where your optic nerve connects to the retina has no light-sensetive cells
• objects appear 33% bigger when wearing a mask underwater because water has a larger refractive index than air and therefore the angle light rays reach your eyes is larger than what it would be in air.
• water attenuates light due to absorption
• as depth increases, the range of visability and intensity of colour decreases due to the diffusion and absorption of light
• as light passes through a greater distance of water, colour is selectively absorbed by water in the order of ROYGBIV
• colour absorption is also affected by turbidity and the concentration of dissolved material
• light attenuation depends on temperature, plankton and concentration of dissolved materials
• light can only penetrate to about 200m (photic zone)
• colour is absorbed in long to short wavelengths (ROYGBIV), red being the longest and violet being the shortest
•  Light attenuation refers to the reduction in intensity of light as it travels through a medium. This phenomenon occurs due to absorption or scattering of photons