Archive | December 2014

How the Eye Works and the Flaws in It.

Don’t get me wrong the human eye is great but there is some flaws in it like, Angle Closure Glaucoma, Macular Degeneration, Detached Retina, and is very susceptible to disease. The human eye does not have that bad of vision compared to other animals out there for example like a skunk they have horrible vision.

What is the structure of the eye? The eye is shaped by the scelera which is the muscles attachment. Ever get blinded by incoming light and then finally able to see after a movie? Well, it is a group effort that allows you to regulate and see. Part of that job is the cornea that refracts the light and the retina is what focuses on the light while the iris regulates the amount of incoming light while the pupil admits the light. The lens are what refracts and focus on the light rays and the Ciliary Body is what holds the lens in place and changes the shape of the lens to help focus. Viterous humor maintains the intracular pressure while transmitting light to the retina and keeps the retina firmly pressed against choroids. Optic Nerves is what transmits impulses to the brain. Choroid is responsible for the absorbtion of strays of light and nourishes the retina.
How do photoreceptors work? Photoreceptors contain chemicals that change when they are hit by light. This causes an electrical signal, which is then sent to the brain along the optic nerve. Different types of photoreceptor allow us to see an enormous range of light: from starlight to full sunshine, and all the colors of the rainbow. We see because we have three photoreceptors, but the animal with the most receptors is sixteen, so what orange to us may be different to an animal that has sixteen. We see what we see because of the three photorecepors that we have that see in red, blue, and green. Though it doesn’t compare to birds who have four photoreceptors that see ultraviolet (UV) as well as red, blue, and green.

How does the eye work? When you look at an object, the light from it enters your eye through the pupil. The iris changes the size of the pupil, depending on how bright the light is. The lens focuses the light onto the back of the eye: the retina. The retina is a mass of light-sensitive neurons, called photoreceptors, which change light signals into electrical ones.

Do humans really see in color? Well, there are two possible answers to this question. First one is how you define ‘colors’. The color of visible light is spread out in the rainbow of the color prism which are a section of the spectrum of electromagnetic radiation. The opposite end of this section are infrared and ultraviolet light, that are invisible to the human eye but some animals are known to detect these. Though these are invisible to the human eye one might not call these “colors” in the sense that you can not see them with the naked eye. So, depending on how you view this, the answer is completely up to you.

There are many wavelengths in the electromagnetic spectrum the human eye cannot detect. We can’t see them because our eyes are not made to see them directly, insects can see other parts of the spectrum of light we can’t. For example, bees and butterflies can see into the ultraviolet, and snakes can see/sense the infra-red that a small mouse emits in the night. We would need special cameras to see those frequencies.

Mantis shrimp have the world’s best eyes.They have up to 16 photoreceptors and can see UV, visible and polarised light. In fact, they are the only animals known to detect circularly polarised light, which is when the wave component of light rotates in a circular motion. They also can perceive depth with one eye and move each eye independently. It’s impossible to imagine what mantis shrimp see, but incredible to think about. Mantis shrimp have compound eyes that are made up of tens of thousands of ommatidia (elements containing a cluster of photoreceptor cells, support cells and pigment cells) much like flies. In the species with spectacular vision, Gonodactylids and Lysiosquillids, the middle of the eye has six rows of modified ommatidia called the mid-band. This is where the magic happy.

Read more at: http://phys.org/news/2013-09-mantis-shrimp-world-eyesbut.html#jCp

Genetics of Eyes

I had a question addressed to me about how genetics play a part in the color of children’s eyes so and I thought it would
be cool to do a blog about it. Next week I’ll also do a blog on the eyes which I can write a lot on.

To start off, if both parents have blue eyes, which I will post diagrams, they will both have the recessive genes for
blue eyes so all their children will have blue eyes. They do not have the dominant gene present to mask the recessive gene. Now if there is a recessive gene (blue) present and one dominant gene (brown) each child will inherit at least one
recessive blue eye gene from the parents. Depending on whether the other gene is dominant or recessive, the couple’s
offspring have a 1 in 2 chance of inheriting blue eyes, and a 1 in 2 chance of inheriting brown eyes. Here in some of
these diagrams you can see that the child could 1 in 4 chance of inheriting two recessive genes and having blue eyes and
a 3 in 4 chance of inheriting a dominant gene for brown eyes. If the brown-eyed child could have either pair of dominant
genes or mixed genes. In another diagram you see all the children will have all brown eyes and this is because the
dominant gene will override the recessive gene.

Eyes differ in colour of the iris, which can be brown, green, blue or other colors. A connection between the HERC2 gene
and eye color has been established. This gene influences the expression of the OCA2 gene, which is involved in creation
of the P protein. This protein is important for normal pigmentation and most likely plays a part in production of melanin.
The amount of melanin influences the color of our eyes. The more melanin is present in the iris, the darker the iris. The
amount of pigment and the pattern of the pigment is determined by a person’s genetic makeup. The DNA received from one’s parents determines what color eyes they will have.

As a fun fact for you is that if a person has two or more eye colors it is called hetrochromia. As an example, a famous
actress, Mila Kunis, has this condition. Hetrochromia is considered an abnormal and may be pathological. Though this has
no medical concern unless it happened over time.
In the world, brown eyed people make up 55% with nearly all individuals from Africa and Asia sharing brown eye color. Most¬†people estimate that around 5-8% of the world’s population has hazel colored eyes. Hazel eyes have a higher concentration of melanin around the eye’s border, which can result in a multi-colored appearance that varies between copper and green depending on the lighting. Now with only 8% blue eyes are genetically recessive, and therefore much less common worldwide.¬†Blue eyed people are frequently found from nationalities located near the Baltic sea in northern Europe. Now with Green eyes being made by only 2%, with me in the category, is most common in northern and central Europe, but can also be found in western Asian cultures on rare occasion.

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(source:pregnancy.familyeducation.com) (source:www.eyedoctorguide.com)