So that made me wonder...well, eye colour! And eyes in general, for that matter. What goes on in those enigmatic eyes of ours? What are they made of? And what is with the different colours? Now, I've got green eyes and from what I took from my science lessons was that it was a mutation. I just felt so cool but then I thought of why couldn't my mutation have taken on a more superheroesque road and felt a little disappointed. But at least I got the power of *sigh* knowledge, and here I impart all of what I've learnt on eyes today!
So, this is the eye, and the simple diagram shows all of what it is made up of. Listing out of all the functions of the separate parts of eye, this should give us an idea of how it works:
- Iris: is a flat, coloured, ring-shaped membrane behind the cornea of the eye, with an adjustable circular opening (pupil) in the centre. It contracts and expands the pupil, in reaction to the brightness of the surrounding light. So think closing your eyes really tightly and opening them up again - the pupils will contract immediately in the light
- Cornea: a transparent layer forming the front of the eye, composed of proteins and cells . The cornea's main function is to refract light. Its transparency of the cornea allows it to refract light effectively. It also prevents foreign matter from entering the eye
- Pupil: the apparently black circular opening in the center of the iris of the eye, through which light passes to the retina. Why apparent - because its just a hole! Pupil size is controlled by the dilator and sphincter muscles of the iris.
- Lens: the biconvex transparent body situated behind the iris in the eye; its role (along with the cornea) is to focuses light on the retina
- Retina: a layer at the back of the eyeball that contains cells sensitive to light, which trigger nerve impulses that pass via the optic nerve to the brain, where a visual image is formed. This one needs to be explained a little further. First thing to understand is that thre are three types of photoreceptor cells in the retina: rod and cones. Rods processes images in low light (imagine a darker setting where its harder to distinguish colours but we can still see objects) Cones allow the processing of detail and colour. The third is ganglion cells, which are information-processing cells, are responsible for sending the images to the brain for interpretation.
- Rods are mainly centered around the retina but not in the forvea where most of the cones are centered
Imagine light is passing through the eye, and at the point where it is inside the retina, it passes through the ganglion cells, bipolar cells, rods and cones. Bipolar cells receive input from the receptors and it is all fed into an optic bundle which makes up the optic nerve.
- Macula: an oval-shaped highly pigmented yellow spot near the center of the retina of the human eye. It absorbs excess blue and ultraviolet light that enter the eye, and acts as a natural sunblock, kind of like the action of sunglasses, for this area of the retina.
- Optic nerve: located in the back of the eye, it is also called the second cranial nerve or cranial nerve II. It is the second of several pairs of cranial nerves. Although the optic nerve is part of the eye, it is considered to be in the central nervous system. Its function is to transfer visual information from the retina to the vision centers of the brain via electrical impulses.
- Vitreous gel: helps the eye maintain a round shape
- Anterior chamber: the fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium
- Not pointed out in the diagram, although you can see it when you notice where the optic nerve exits the eye, but we do also have a blind spot in the eye caused by the absence of specialized photosensitive cells, or photoreceptors, in the part of the retina where the optic nerve exits the eye. What we then can't see is simply made up by the brain. There is a trick to noticing your blind spot, see it here when you click of this link and follow the instruction: http://serendip.brynmawr.edu/bb/blindspot1.html
So what determines colour in our eyes?
Simply put, genetics! So let's say there is a mother and father, and they both have brown eyes, their combinations can only make brown-eyed children. And that is the same with two blue-eyed children. However, when you get a blue-eyed mother and a brown-eyed father, it's suddenly a little different, leading us to the understanding (science just loves being complicated) of the dominant and the recessive geneology here - brown eyes are dominant and blue eyes are recessive. So to picture this, a brown eye can be symbol as B and a blue eye can be a symbol for b. The chances then are still all brown eyed children if the brown-eyed parent had the gene BB (both dominant for brown eyes). If the brown-eyed parent had a Bb gene, then the chances are for a blue-eyed child 1 out of 4.
So what's with green, hazel, amber (yes, people have amber eyes. I am so jealous), grey, red/violet eyes?
This is to do with a melanin and liopchrome ratio in our eyes.For example, amber eyes have very low melanin and a high amount of lipocrhome and grey eyes have a low amount of melanin and no lipochrome.
Iris color is highly complex phenomenon and consists of a combined effect of texture, pigmentation, fibrous tissues, and blood vessels in in the iris stroma. Melanin is a yellowish-brown to dark brown in the stromal cels and black in the iris which lies in a thin later across the back of it. Most human irisies show a condensation of the brown melanin layer which by its position has an influences over the overall eye colour. the degree of dispersion has some influence over the eye colour. People with severe forms of albinism may appear to have red eyes under strong lighting due to the extremely low quantities of melanin.
I had fun reading up on all this eye madness, hope you had fun reading about it!
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