Human Eye Anatomy

7/28/2019 Human Eye Anatomy

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Human Eye Anatomy:Parts of the Eye

ByLiz Segre; eye illustration byStephen Bagi

The human eye has been called the most complex organ in our body. It's amazing that something so

small can have so many working parts. But when you consider how difficult the task of providing

vision really is, perhaps it's no wonder after all.

(Mouse over the words in the eye anatomy illustration below for their definitions.)

How the Human Eye Works

In a number of ways, the human eye works much like a digital camera:

1. Light is focused primarily by the cornea the clear front surface of the eye, which acts like a

camera lens.

2. The iris of the eye functions like the diaphragm of a camera, controlling the amount of light

reaching the back of the eye by automatically adjusting the size of the pupil (aperture).

3. The eye's crystalline lens is located directly behind the pupil and further focuses light. Through

a process called accommodation, this lens helps the eye automatically focus on near and

approaching objects, like an autofocus camera lens.
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4. Light focused by the cornea and crystalline lens (and limited by the iris and pupil) then

reaches the retina the light-sensitive inner lining of the back of the eye. The retina acts like

an electronic image sensor of a digital camera, converting optical images into electronic

signals. The optic nerve then transmits these signals to the visual cortex the part of the

brain that controls our sense of sight.

Parts of the Eye, as Seen From Above

(Please Mouseover the Labels to Learn More)

For more detailed information, please read the article on"Refraction and Refractive Errors: How the

Eye Sees."

Other parts of the human eye play a supporting role in the main activity of sight:

Some carry fluids (such as tears and blood) to lubricate or nourish the eye.

Others are muscles that allow the eye to move.

Some parts protect the eye from injury (such as the lids and the epithelium of the cornea).

And some are messengers, sending sensory information to the brain (such as the pain-sensing

nerves in the cornea and the optic nerve behind the retina).
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Anatomy of Attraction: The Science Behind Love at First Sight

February 2013 Ever wonder about the meaning behind the phrase "the look of love"? When

you're gazing into your partner's eyes this Valentine's Day, pay some thought to the science

behind love at first sight.

The connection between eyes and love is well-documented in poem and prose since time

immemorial, the stuff of whimsical fairytales and heroic legends. But while beauty may be in the

eye of the beholder, evidence increasingly suggests our brains are hardwired to both display and

notice visual "clues" when it comes to a potential love interest.

One such indicator of visual attraction is larger pupils. Studies show that our pupils dilate when we

feel excitement and attraction. When our gaze falls on a person or object of interest to us, the brain

releases a surge of dopamine (a chemical messenger that helps control the brain's reward and

pleasure centers), which triggers pupil dilation.

Men perceive women with larger pupils as more romantically appealing. A 2007 study published

inHormones and Behaviorshowed that a woman's pupils dilate the widest during ovulation. From a

biological perspective, because this characteristic is developed under the influence of estrogen, it

signifies youth and therefore fertility. Research suggests that men instinctively use such indicators,

among other visual cues, to assess the "value" of potential partners as a way to seek fertile and

healthy mates.

Similarly, researchers at Edinburgh University found that women at their monthly fertility peak are

most attracted to men with larger pupils. According to the study published in the journal Personality

and Individual Differences, larger pupils signal a man's interest, and therefore he is more indicated

as a partner because interest is mutual. Conversely, the study found that when women are notat

their most fertile, men's pupil size make very little difference when looking for a mate.


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Lingering eye contact also is a strong indicator for a potential love match. A 2009 study published

inArchives of Sexual Behaviorfound that a man who rated a woman as attractive held eye contact

for an average of 8.2 seconds, which increased his chances of "love at first sight," researchers

said. If a man's gaze was around 4 seconds, the research suggests he was less than impressed.

When it comes to eye color and attraction, green eyes are seen as most attractive, according to an

AllAboutVision.comeye color pollof more than 46,000 people. But when it comes to matters of

the heart, research suggests most people do not have an eye color preference. In fact, it appears

"the look of love" is all about the pupils.

So this February 14th, look into your Valentine's eyes chances are his or her pupils will be

dilated! A.S.

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[Page updated February 2013]

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Human Eye Anatomy