How do eyes see?

The eyes interact with our visual surrounding with the help of the brain. The main purpose of the eye is to send images to the brain which then interprets them. The other body parts are instructed by the brain to perform accordingly after the visual is assimilated by the brain. This is how we see and interpret the images.

Sensitivity (ISO)

The ISO of our eyes is similar to that of a camera. In brighter conditions, the ISO of our eyes drops thus giving finer and brighter details. In darker conditions, the ISO rises. This is also termed as ‘Dark Adaptation’. You may be already aware of the fact that darker areas look granular and fuzzy. This is the result of the ‘climbing’ ISO. In the dark we only see black and white. The human eye is designed to ‘see’ in the darkest conditions. Our eyes adjust very quickly to bright conditions while it takes more time to be comfortable to darker conditions.

To look well in the dark, try a side view as the center of the eye is insensitive to dark.

Region adaptable ISO

The retinas in the human eye can adjust to variations in regions. There is a drop in the sensitivity when it’s a bright sky while for a darker foreground, the sensitivity rises.

High dynamic range

This is done by the eyes with the help of the region-specific adaptation. Till now, there hasn’t been a suitable technology to mimic this eye range.

White balance

The white balance is something that is done by the brain. It varies with the levels of light. In photopic (bright) conditions, we are less sensitive to blue hues than when we are in scotopic (dark) conditions. This is why bonfires in photographs look extra reddish, and we have to apply a red eye correction for a more natural image through the camera lens.

Focal length

Focus is achieved by stretching and squeezing our eye lenses. The focal length is adjusted to the eyeball size.


The black spot at the centre of the iris acts as our aperture. The aperture decreases in diameter when in bright sunlight to as much as 1 mm. At night time, however the aperture diameter is close to 9 mm.


In case of the eyes, the eyelids act as the shutter. The human vision depends on exponential decay.


The resolution of the human eye is about a sixtieth (60th) part of a degree.


The central spot in the iris is responsible for the things we see. The brain stitches together images so that we perceive the exact images that are present. It’s like the video mode of cameras. Several still images run one after another at high speeds to give the perception of a moving object.

Function of the brain

The brain is solely responsible for the vision. The eyes by themselves see nothing. The eyes merely send visual signals to the brain which interprets them and orders us to act accordingly. Thus, the eyes are just a medium.

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