Basic Structures of the Eye

Here is a set of notes I took about the basic structure of the eye. Enjoy! (The image is a focused shot of my right eye.

Visual process/ basic optical system - When a person looks at an object, the light rays that will reflect off the object enter the eye through the front and into the back of the eye. During the process, the light rays are bent and produce an upside-down image onto the retina. This image is then turned into electric impulses that travel to the brain where the image is translated and the object is then able to be perceived as upright. Light enters the globe through the cornea to the lens which also helps to bend the light and the light then travels through the vitreous to the retina where the information is changed into the electrical impulses and sent to the brain by the optic nerve.

Globe- the structures and membranes that together comprise the solid round shaped eyeball.

Cornea- the outermost front part of the globe. It is a thin, tough, crystal clear membrane that is sometimes called the window of the eye. It is transparent due to a lack of blood vessels which distinguishes it from other tissues as the cornea receives its nourishment from the tear film that covers its surface and a specialized fluid that flows beneath it. It provides 2/3 of the total refractive power of the eye and is the chief refracting tissue. There are five layers to the cornea body

-------- Corneal epithelium - first line of defense against injury and infection.
-------- Bowman's membrane - this membrane serves as the anchor to the epithelium layer.
-------- Corneal stroma - the main body of the cornea and contributes rigidity to the cornea. 90% of corneal thickness
-------- Descemet's membrane - provide some rigidity to the corneal body; a thin layer of collagen and elastic fibers
-------- Corneal endothelium - has cells that service pumps to maintain a proper fluid balance in the cornea and also help provide nutrients to the whole. It is a layer of delicate cells that cannot regenerate.

Sclera - the white tissue surrounding the cornea which is a strong fibrous outer layer that helps protect the intraocular parts and structures. So the white of the eye is actually bulbar conjunctiva which is translucent over the tissue of the sclera. Covers over 80% of the eyeball including whole of the rear.

Limbus - the juncture between the sclera and the cornea. The bulbar conjunctiva terminates here.

Anterior chamber - the area between the cornea and the iris. It is a small compartment filled with a fluid called aqueous humor that helps nourish the cornea. It is deepest at the center.

Iris - this structure is a colored diaphragm of tissue that is stretched across the back of the anterior chamber. In essence, creating the chamber between itself in the cornea. Using both a dilator muscle and a sphincter muscle, the iris can make the hole in the center pupil larger or smaller to control the amount of light that can be captured by the inside of the eye. It controls the pupil by involuntary reflex.

7. Pupil - this is not an actual structure; simply a name for the absence of structure or the hole in the center of the iris. The iris controls the size of the pupil and aqueous humor flows through it into the anterior chamber. It appears black because there is no light in the back of the eye to shine through to the front.

Lazy Day at Home

I've been fighting a migraine most of the day. They are always the same. Smells and light feel to strong and to bright... I feel painfully aware of them. The smell of something I would usually find pleasant now hurts and makes me wince and makes my breathing hitch because the more I smell the worse it gets. The pressure builds around my left septum and up through the left side of my head and as it feels like everything is swelling, I feel the vision fade. As the pressure builds up, I watch my vision in my left eye fade and more towards my nasal cavity ... so that looking straight ahead can make seeing anything on the left side impossible with only a little visual help from my right eye. I haven't used Relpax in awhile, but I eagerly sought it out today. In two hours I decided I needed another tablet and my vision was so screwy and the tablet so well protected in its tight sheath that I was unable to open it. I was able to have the second dose only after using scissors to try and break it out and when that failed, the small child I was watching opened it for me. (It is a bizarre testament to the strength of the packaging that nothing I could do opened it, but a six year old child with nails opened it with ease.... and yes, I showered her with gifts afterwards.)

I am so grateful that I was able to stay home today. If I had gone and had to drive back in the storm I am not sure I would have made it home safely. The opportunity to end this day sitting in the dark watching the blizzard outside from the warmth of the couch. The words 'bomb cyclone' sounded really scary... and I think it would have been if I had been out it in... but I feel safe and warm inside my home. I have so much in my thoughts right now, but I have much to be grateful for too. I hope for all to be warm and safe tonight.

Short Definitions of Color

Sir Isaac Newton discovered that color is a “direct function of light + that whole light is a mixture of all the colors of the rainbow and named that idea/ process ‘the spectrum’. So even when we do not see color I light it is there and is what creates the colors we see- neither exists without the other. When we organize the visible spectrum of color into a circle, we get an image of the conventional color wheel.

There are three primary colors: red, yellow and blue. These colors are colors in their own right… in a sense pure, because you do not have to mix colors to come up with them. There are three secondary colors: orange, green, and violet… which are created with a mixing of two of the primary colors together to create the secondary shade. Intermediate colors are created when we mix primary colors as well as a secondary color that neighbors the primary on the color wheel.

The subtractive process of color mixing happens when we mix colors together from a light color to an end result of black due to the mixing of so many colors- black is the absence of discernible color. In this sense, light seems to also be absent as it cannot radiate any of the colors once they have been mixed to black.

Color saturation refers to the intensity or visible sensation of purity of color. It can also refer to how different a color is from white and the ‘strength’ of its visual ‘pull.’

A complementary color scheme is use in works that use hues of color that lie opposite of each other across the color wheel which helps to make both looks look more intense and to complement each other. When an artist uses this effect, it is called simultaneous contrast due to how the human eye registers and recognizes color and how our brain interprets it. As the retina can only respond to one color at a time, our perceptions of each color seems to be stronger and more highly focused. Analogous color scheme are works that are created using colors that are next to each other on the color wheel… These colors can tend to appear to blend into each other and even bring other views of each color out with the way the light around the work hits and amplifies the images. Analogous colors usually are sorted according to temperature, while complimentary colors tend to be brought out by opposition.

Color can be ‘sorted’ by temperature which is a way of describing the light measured in degrees of Kelvin. An easier way to look at color temperature is to recognize that this is a way to describe the characteristic of light in term for temperature- either warm or cold… or variations of those descriptions.

2014 Poetry Corner # 11 : "Eye" (a haiku)

Bright light pours in
The pupil contracts, we blink
the world is clear

2013 Poetry Corner #4 : A Sister in Sacrament Meeting

Light wavy tresses
mingling with light and dark
flowing softly, lightly down
framing her face, her eyes, her smile
head poised, listening
calmly focused, peaceful, silent
A virtuous woman before God