Tag: human eye

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Amazing Human Eye

Amazing Human Eye
Eyes are among the great challenges to those who insist that unguided, naturalistic evolution created all living things. Eyes are complex devices that display engineering design skill. A significant problem for naturalists is that some very complex eyes appear early in the fossil record, such as the trilobite eye. Each animal has eyes well-designed for the life they live. That is certainly true of the amazing human eye.

Many things about human eyes make them amazing. One of those is the cornea, the clear front covering of our eyes. Corneas must be perfectly clear to allow light to pass through for an unobstructed view of the world around us. Because of the need for complete transparency, they have no blood vessels. Our corneas get their nourishment from the aqueous humor (the liquid inside the eye) and the tear fluid on the outside. They get oxygen from direct contact with the air.

Corneas must be designed to fit a curving surface full of a fluid which maintains the critical pressure inside the eye. However, there is a problem with the cornea being exposed to the air with all of the contaminants it contains – pollen, dust, chemicals, and grit. Corneas can become scratched. Over time, any surface exposed to dirt and grit, and sometimes bumps and blows, can get tiny scratches. How is it possible for corneas to remain transparent with so much abuse?

When you cut your skin, as the cut heals, scar tissue forms. Scratches in our corneas must heal without scar tissue. When the outer layer of the cornea gets scratched, the surrounding cells move toward one another and close the scratch leaving no scar tissue. This is only one feature of corneas which consist of five different layers each having an important function and showing evidence of design.

Think what it would be like if scar tissue formed every time the surface of our corneas got scratched. By the time we reached middle-age, we would certainly be looking through cloudy lenses. If you can read this, you should be thankful for just one of the features of the amazing human eye!
–Roland Earnst © 2018

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Types of Tears – There are Three

Types of Tears – There are Three
In April of 2016, I received a note from Charles and Brenda Beard who asked if I had ever studied the subject of tears? I put that in my list of topics to investigate thinking that types of tears could not be very complicated. There should be only one type of tears that came with different kinds of situations. Upon researching tears, I have learned that there are three types of tears, and they are different in function and different in composition.

BASAL TEARS keep the cornea of the eye continually wet and nourished. They also lubricate the eye and keep it free of dust. Tears of this type contain water, mucin, lipids, lysozyme, lactoferrin, lipocalin, lacritin. immunoglobulins, glucose, urea, sodium, and potassium. The substances such as lysozyme fight against bacterial infection by dissolving a layer in the outer coating of certain types of bacteria. This action is part of the body’s complex immune system.

Basal tears also contain antioxidants including ascorbate, urate, cysteine, glutathione, and tyrosine. For those of us that aren’t biochemists, this simply means there is a complex, designed system in the tear production of our eyes. This system keeps this vulnerable, exposed surface from being destroyed by agents in the world around us that would attack such a sensitive area.

Typically a person will secrete .03-.04 ounces (.75-1.1 grams) of this body fluid per day. If you have had a family member or even a pet that could not produce tears, you know that very quickly the eye becomes unusable. Basal tears are a carefully compounded chemical substance essential to our vision.

REFLEX TEARS attempt to wash away anything that irritates the eyes. When foreign particles or irritants contact the eye or nasal area, TRP (amino acid) channels in the ophthalmic nerve act to produce these tears. Most of us have produced tears when working with certain substances such as when cutting onions. Tear gas, pepper spray, or some fragrances cause this same reaction. Yawning, coughing, or vomiting can trigger these tears. Bright lights shining in your eyes or hot, peppery substances in your mouth also trigger reflex tears. The fluid, which is water laced with amino acids, help to wash away the irritant.

Those are two types of tears that are very important. There is also a third type which we will talk about tomorrow.
–John N. Clayton © 2018
Data from the American Academy of Ophthalmology.