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How Does the Eye Work

Omkar Phatak Apr 7, 2019
An eye is one of the most delicate and the most important parts of the human body. If you have ever wondered how eyes work to enable the perception of nature and all its manifestations, this write-up will be an interesting read.
'Beauty is in the eye of the beholder...'

Appreciation or perception of beauty is relative and in reality, beauty lies in how we look at things, than how things are.
Amongst the instruments of our mind, which bring knowledge to it, an eye is perhaps the most important one. If it wasn't for these amazing instruments that we possess, we would never have been able to appreciate the true beauty of nature and understand where it lies. One wonders how these instruments that enable us to see, work in actuality.
Most of our modern technological innovations, consciously or coincidentally mimic phenomena in nature. The study of bird flight, inspired the first airplane models. Sonar mimics a mechanism by which bats see sound waves. Similarly, the modern camera mimics the working of the human eye.
People may have been inspired by the working of the human eye to build the first cameras. In this article, we will go in reverse mode and understand the working of an eye, through the analogy of the working of a camera.
Of course, the eye is far more advanced than a camera, in terms of how it perceives color, depth, or three-dimensional vision, its adaptive optical mechanism, and how brain interprets the image input that it receives. However, at a basic level of functioning, both are inherently similar.

The Working of the Human Eye

Let us study the whole process of vision perception, right from the moment light reflected, refracted, and emitted by various objects around us, reaches the surface of our eyes. We will track the path of that ray of light, further inside.

Cornea: The Lens Shutter

Cornea is the outermost part of the eye and its working is akin to a lens cover. It is the primary element that focuses diverging light to converge onto the insides of the eye. It is made up of an outer layer of epithelium, whose function is to protect the inner eye.
It is made up of transparent regenerating cells, that make the passage of light through it possible. Light is bent when it passes through the cornea and falls on the pupil.

Pupil and Iris: The Aperture Mechanism

Pupil is the central black circle and iris is the concentric colored circle around it, that together constitute the aperture mechanism of the eye. Pupils dilate or contract according to the amount of incident light.
In low light condition, it dilates to gather more light, while in bright light, it contracts to prevent damage, from overexposure. Light passes through the pupil and falls on the lens.

The Eye Lens

The lens is the main focusing mechanism, that bends light and makes it fall on the retina. Sometimes, with age, this lens becomes cloudy and opaque (called a cataract condition) and then needs to be replaced through surgery. The ciliary muscles, attached to the eye lens, control its curvature and thereby control the focal length of that lens.

Retina: The Photoreceptor or Camera Film

Light bent by the eye lens, falls on the retina, which forms the photo receptor mechanism of the eye, similar to a camera film. Retinal nerve cells are some of the most special cells of our body. They generate electrical signals, in response to the light falling on them. The retina contains special cells called 'Rod Cells' that help in perceiving color.

Optic Nerve and the Brain: The Image Transport and Processing Mechanism

The electrical signals generated by the retinal nerve cells are then transported towards the optical processing mechanism in the brain called the optic chiasma, via the optic nerve. The point where the optic nerve is connected to the retina, doesn't have nerve cells.
Hence, light falling on this spot is not processed and is called the blind spot. There is one piece of every image, which is missing in every frame due to that spot. Real images formed by lenses are always flipped upside down.
That means, we should also see inverted images through our eye lens. However, that doesn't happen as the image is inverted again by the brain. That is why, we don't see it to be inverted.