The eye is a sense organ which allows us to see the “world”. In scientific terms the eye is called the sight organ, the organ of vision and is also sometimes called as Photoreceptors.
There are different organisms living on this planet which have different kinds of eyes and all the characteristics related to it.
An eye basically is one of the five sensory organs along with the nose which allows us to smell, the tongue which allows us to taste the food, the ears which allow us to hear the sound in our surrounding and our skin which allows us to feel the touch when we touch any object.
The eye as we all know is a very complex organ and its characteristics change from species to species. For example, a human eye will allow us to see but will have different characteristics from that of the cat’s or dog’s eye.
The Human Eye and its Parts
The eyes are always present in pairs to give a 3D vision and it is present in the bony socket of the skull. Therefore, it is well protected.
The eyes consist of different components like the pupil, the iris, the lens, the lachrymal glands, the eyelids for protecting the eyeball, the sclera, the retina and many more components.
Each one of these have their own unique function which when put together allows us to see the desired object.
The pupil is like a black spot in the middle of the cornea surrounded by muscles of iris. This iris is the surrounding region of the eye which is unique in its colour and nowadays used in the biometric system.
The dilator muscles or sphincter muscles in the iris will adjust depending upon the light intensity and hence, will contract or dilate the pupil to avoid any damage to the lens of the eye by the light.
The lens is present behind the pupil and from the lens there is a continuation till the retinal veins and the optic nerve which is called as retina.
Aqueous Humour or Vitreous Humour is a watery fluid present behind the lens and between the retina of the eye.
The retinal cells produce this vitreous humour and it is nutritious as it contains proteins, salts and water. The retina is rich in oxygenated blood supply and here, the light information is converted to nerve impulses.
The sclera is the white portion besides the pupil and the iris and it is also supplied by the blood because of which we see the red lines on the white portion of the eye.
The optic nerve carries the information from the retina to the brain and produces the image from the information given by the retina.
Eyelids are protecting parts of the eye which are present outside the eye.
Then comes the lachrymal glands or tear glands which secrete tears which are salty, and they are basically secreted to clean the eyes or remove the dust particles which are settled on the eyeball and also sometimes, notify the person’s emotions.
How does the Eye Work?
The blinking of the eye is very rapid i.e. within a minute there will be a lot of blinking. This rapid blinking is especially seen when the person feels that his/her eyes are threatened.
The blinking of an eye is a reflex reaction similar to a knee-jerk reaction.
This involves a very complex interaction. This interaction consists of the interaction between the eye, the nervous system and the brain.
Light is very much required to see the surrounding objects. Whenever light falls over any object, some of the light is reflected back and some of the light is absorbed by the object.
The light which is reflected by the object when it falls on that object is what is seen by the eyes.
It very important to understand that the eyes allow us to see the light which is reflected back by the object and not the light which is absorbed by the object.
The light which is reflected then falls on the pupil and then further enters the lens which is present behind the pupil and then further reaches the retina.
Here, the light energy is converted into nerve impulses. These nerve impulses are then carried through the optic nerve to the brain where the information is processed and then an image is formed. This image is what we see.
Different Animals with different Eyes
Yes, it can also be said that different animals have different vision due to different characteristic feature of their eyes.
For example, the image which is produced by the human eye is of a defined frequency and wavelength which lies in the visible range of wavelength i.e. humans and some other animals see in the visible light from 400nm to 700 nm.
There are some animals which have eyes different from that of a human. The difference over here is that the animals can see the Ultraviolet (UV) light that is below 400 nm. The animals which can see UV light are reptiles, birds, etc.
Reindeers can see UV light due the phenomenon of reflection of the sunlight on the white snow. This all happens due to the different pigments present in the lens of the eye which filter the light falling upon it.
There are also some animals which see in monochrome that is black and white colour. This is due to the presence of the photoreceptor cells called as rods and cones.
The rods work in a dimmer light as compared to that of the light required by the cones to work.
The difference is that these cones and rods will send the electrical signal through the retina depending upon the intensity of light.
Another distinguishing characteristic is that of colour of the eyes. The human eyes are generally light brown i.e. most common characteristic due to the presence of the melanin pigment.
The blue or green colours of the eyes are due to the scattering of light inside the stroma.
There are many different species of birds having different eye colours due to the presence of different pigments like carotenoid, purines, etc.
The colour of the eyes depends upon the genetic makeup of that particular species and not due to any recessive or dominant trait.
Along with different components of eyes, each and every animal has different vision, different requirements to see the object in that particular light intensity.
This is what makes the eye very interesting as well as attractive given the right colour and features.