The individual can see six times better in the dark than a regular human. Trion has acted on the individual's eyes, changing the anatomy of the eye, causing them to have an increased ability to see in low light levels. This is due to a change in the ratio of photoreceptor cells found in the eye.
Anatomy of the Eye
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Retina: A layer at the back of the eye, containing photoreceptor cells that captures incoming light in the form of photons and converts them into electrical signals.
Rod Cells: One of the two photoreceptor cells that handles vision in low light levels. They do not facilitate colour vision and operate in grayscale with a low level of visual clarity.
Cone Cells: One of the two photoreceptor cells that handles vision in medium and high light levels. They facilitate colour vision and operate in a additive colour scale (red, green, and blue) with a high level of visual clarity.
Macula: A small depression in the retina that produces sharper vision than the rest of the retina. It contains both rod and cone cells, with a higher ratio of cone cells.
Fovea Centralis: The small, centre-most point of the macula that produces the sharpest area of vision. It contains only cone cells.
Iris: The coloured part of the eye that surrounds the pupil. It regulates the amount of light that enters the eye through the pupil by dilating (making it larger) and constricting (making it smaller) it.
Pupil: The black part of the eye. It is the opening at the centre of the iris that allows light to enter the eye and hit the retina.
Explanation
In the eye of a normal human, the cone cells are concentrated around and in the macula, while the rod cells around are more concentrated around the periphery of the retina. This makes sense because one can not determine the colour or size of an object in their peripheral vision, however the peripheral vision is very good at picking up on movement. The central vision allows one to determine the colour and size of the object due to the concentration of cone cells in that area of the retina. Normally, there is a ratio of 20 rod cells:1 cone cell. This allows humans to have a very good vision that detects both movement and colour, while being able to distinguish the features of what one looks at.
In the individual's eyes, the ratio of photoreceptor cells is 25 rod cells:1 cone cell. This allows the individual to have an enhanced ability to see in low light levels, akin to a cat's vision. Unlike a cat, the macula is still present so the individual is not myopic (nearsighted) and their detail-oriented vision is still intact.
However, due to the eye only being able to contain a certain amount of photoreceptor cells, the individual's colour vision is worse than that of a normal person. This is due to the ratio changing but the amount of cells allowed staying the same. Therefore, there are less cone cells in comparison to rod cells in the individual's eyes. The individual can still see the full visual spectrum, but it is much more muted.
This ability would have no effect when the individual is in a trion as long as they have an operator, due to the operator being able to activate night vision for the individual. It also wouldn't have much help in a fight between individuals in a trion body that can also use the night vision function. However this could shine for infiltration when the individual is in their real body. I think the concept is interesting.
