Oxnard - Port Hueneme Optometry  Dr. Don Steensma 465 W. Channel Islands Blvd, Port Hueneme, CA 93041  805/486-3585

Why our vision does not go black when we blink?

Researchers have found that visual sensitivity starts decreasing just before we blink.

In a recent study, scientists put powerful fiber-optic lights in the mouths of people. The lights were strong enough to penetrate the roofs of the test subjects mouths and strike their retinas, so they would perceive the light  They wore goggles to block any outside light.

When the test subjects blinked, the amount of light actually stimulating the retina didn't change. During blinking however, brain activity as measured with an MRI was suppressed in areas that respond to visual input.

If visual awareness was not suppressed during blinking we would be constantly aware of the eyelids sweeping down over the pupil during a blink and the world going dark.


Why do blind people seem to have the same day time - night time time cycle that sighted people have?

You would think that a blind person who could not see that its day time or night time might eventually get out of kilter with his sense of what the true time is.  If they were isolated by themselves without an obvious way of marking time you would think they might start waking up an hour sooner or later and eventually be on a different schedule than a sighted person.

In more primitive animals like a squid, a light sensitive spot on the forhead skin senses the presence  of light and regulates the  time cycle. In the human that light sensitive tissue  lies deep in the brain within the skull and can not sense light directly.  It is called  the Pineal gland.

Recent research has found that retinal cells called  intrinsically photosensitive retinal ganglion cells, or ipRGCs are the reason. The ipRGCs reside deeper in the retina than the cones and rods - the millions of eye cells in the retina which send visual information to our visual cortex. Only numbering between 1,000 and 2,000, ipRGCs gauge the overall light intensity and relay this information to the Pineal Gland.

This direct link explains how some blind people can still have the same daily internal rhythm as a sighted person.  So an extremely ancient system in terms of evolution has been adapted to our present minds.


Why does the sky look blue?

Blue light has a short wavelength, and the particles in the air scatter the light around, making the sky appear blue. Red light has a longer wavelength, which is not scattered as much. Sunsets are red because in the evening, the light has more atmosphere to pass through to get to your eye, and only the strong red light can penetrate.   At least that is the traditional answer to why the sky is blue.

But it's a little more complicated than that.  The human eye is sensitive to light between 380 and 740 nanometers.  An average retina has 10 million rods for sensing low light levels and 5 million cones for detecting color.  Each cone contains pigments that are sensitive to specific wavelengths.  There are three types of cones for long, medium and short wavelengths and you need all three of them to see color correctly.

The peak response for the long cones is at 570 nanometers (yellow), medium at 543 nanometers (green), and short at 442 nanometers (between violet and blue).  But the three types of cones are sensitive over broad, overlapping wavelength ranges, which means two different light spectra can cause the same response in a set of various cones.

The same principle that makes red and green turn into yellow is happening in the sky.  But in this case, the sky's combination of violet and blue elicits the same cone response as pure blue plus white light, which is an equal mixture of all the colors.   So your eye can't tell the difference between that complex spectrum and one that is a mixture of pure blue and white.  So the sky is blue due to scattering of light and the cone function.  Most animals have only two types of cones instead of three that we have so the sky probably appears a slightly different shade to them.  Honeybees and some birds can see ultraviolet wavelengths that are invisible to humans.


Why doesn't  the world seem to move when we move our eyes quickly from one spot to another?

If our eyes follow an object (a "pursuit" move) things are pretty straight forward but if our eyes jump from one fixation point to a different fixation point (a "saccade" movement) it's a lot more complicated.  As our eyes jump from one point to the other our point of reference changes and we would perceive a movement of our surroundings.  To avoid a constantly moving landscape about us the brain blocks new visual stimuli  for a few milliseconds during the movement.  We retain the previous view until the new view is established.


What is Palming or The Bates Method

Dr William Horatio Bates was an ophthalmologist who devised a theory in 1891 that vision could be improved by performing a series of eye relaxation techniques. He felt that eyeglasses were a crutch that could be avoided if you used his techniques.

The primary exercise was called "palming". In palming you cover your eyes with the palms of your hands blocking all the light. It was done several times a day. Other methods used included "Swinging" (swing your upper body from side to side), "Sunning" (gazing at the sun through closed eyelids), and "Blinking" (rapid fluttering of the eyes).

The problem with the Bates Method is that it simply does not work. If it did work I would be doing it on myself as well as on my patients.


Misc:

Your eyes are really a part of your brain.

Most of the eye is protected by the bones of the orbit.Only 1/5 of of your eyeball is unprotected.

The average person blinks 12 times per minute or 10,000 blinks each day.

It is impossible to sneeze with your eyes open.

Our eyes contribute 85% of our sensory input.

About one third of our brain is devoted to seeing.

The older we are the less tears we produce.

There are 6 extraocular muscles controlling the movement.

There are 2 muscles that control pupil size.One makes the pupils larger and one makes the pupils smaller.

Colorblind people see colors but do not see the difference in some colors.

Red and green are the colors most often confused in colorblind people.

About 5% of males are color deficient.

Color deficiency is very unusual in females.

At birth a child's eyes are 75% the size of adult eyes.

By age 7 the eye is the size as an adult eye.

There are 2 tear drainage ducts in each eye that drain excess tears into the nose.

The right side of the brain sees to the left side in both eyes. The left side sees to the right in both eyes.

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