Difference between revisions of Eyeballs

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* '''Lens''' - The part that changes the focus distance of the eye

* '''Rods and cones''' - Rods and Cones are the sensory cells in the back of your eye that detect light.

** Rods sense only light intensity, not color. They ~~sense edges~~ more ~~sharply than cones~~. If you are outside at dusk, you may feel a sudden switch of your vision from color vision to black and white, this is your [[visual cortex]] switching to only rod input when cone input isn't working as well in dim light.

** Rods sense only light intensity, not color. They require lower levels of light to trigger, and so work better in low-light conditions. They are more sensitive to movement, and tend to be concentrated on the periphery of the retina. If you are outside at dusk, you may feel a sudden switch of your vision from color vision to black and white, this is your [[visual cortex]] switching to only rod input when cone input isn't working as well in dim light.

** Cones are the cells that detect color in your eye. There are three different types of cones that respond most strongly to three different wavelengths of light. Your visual cortex takes the combined response of the three types of cones and makes up the blended color in your mind. Magenta for example is an imaginary color. It's the color your brain makes up to explain why both short and long wavelengths of light are detected, but not the wavelengths in the middle. Most colors are on the color spectrum you learned in school (Red, Orange, Yellow, Green, Blue, Indigo, Violet), and will trigger a single cone type, or two adjacent cone types.

** Cones are the cells that detect color in your eye, but require much higher light levels to trigger. They concentrated in the macula, where high-resolution acuity is required. There are three different types of cones that respond most strongly to three different wavelengths of light, though there is a large overlap. Your visual cortex takes the combined response of the three types of cones and makes up the blended color in your mind. Magenta for example is an imaginary color. It's the color your brain makes up to explain why both short and long wavelengths of light are detected, but not the wavelengths in the middle. Most colors are on the color spectrum you learned in school (Red, Orange, Yellow, Green, Blue, Indigo, Violet), and will trigger a single cone type, or two adjacent cone types.

* '''Retina''' - the tissue that supports the rods and cones.

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* '''Vitreous humor''' is the clear gel filling the majority of the eyeball. It is where true [[floaters]] live. This gel is important for helping the eye hold its shape and maintain the correct pressures inside the eye even when air pressure changes. In adults, the gel has a complex structure, with different thicknesses in different parts.

* '''Vitreous detachment''' is attached to the outer wall of the eye in multiple locations, but can become separated. When separated from the retina it does not support the retina fully, and puts you at higher risk for [[retinal detachment]]. It can also leave behind a large [[floater]] that impairs vision.

* '''Extraocular muscles''', the six muscles that control movement of the eye and one muscle that controls eyelid elevation.

== Axial Length ==

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== [[wikipedia:back of the envelope|Back-of-the-envelope]] calculations ==

We can use [[Optics related math]] and some very approximate numbers to give order-of-magnitude estimates of some of the ~~quanties~~ involved.

We can use [[Optics related math]] and some very approximate numbers to give order-of-magnitude estimates of some of the quantities involved.

To estimate the focusing power of an [[emmetropic eye]], we might take the [[axial length]] as around 2.5cm. For [[distance vision]] (parallel incident light) that number is simply the [[focal length]] of the eye at rest, giving 40 [[Diopters]]. If we take the [[near point]] as about 25cm, that requires an additional 4 dpt of focusing power from the lens.

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==See Also==

* [[Duochrome Test]]

* [https://en.wikipedia.org/wiki/Human_eye Human Eye] (Wikipedia)

==References==

@@ Line 9: / Line 9: @@
 * '''Lens''' - The part that changes the focus distance of the eye
 * '''Rods and cones''' - Rods and Cones are the sensory cells in the back of your eye that detect light.
-** Rods sense only light intensity, not color.  They sense edges more sharply than cones.  If you are outside at dusk, you may feel a sudden switch of your vision from color vision to black and white, this is your [[visual cortex]] switching to only rod input when cone input isn't working as well in dim light.
+** Rods sense only light intensity, not color. They require lower levels of light to trigger, and so work better in low-light conditions. They are more sensitive to movement, and tend to be concentrated on the periphery of the retina. If you are outside at dusk, you may feel a sudden switch of your vision from color vision to black and white, this is your [[visual cortex]] switching to only rod input when cone input isn't working as well in dim light.
-** Cones are the cells that detect color in your eye.  There are three different types of cones that respond most strongly to three different wavelengths of light.  Your visual cortex takes the combined response of the three types of cones and makes up the blended color in your mind.  Magenta for example is an imaginary color.  It's the color your brain makes up to explain why both short and long wavelengths of light are detected, but not the wavelengths in the middle.  Most colors are on the color spectrum you learned in school (Red, Orange, Yellow, Green, Blue, Indigo, Violet), and will trigger a single cone type, or two adjacent cone types.
+** Cones are the cells that detect color in your eye, but require much higher light levels to trigger.  They concentrated in the macula, where high-resolution acuity is required.  There are three different types of cones that respond most strongly to three different wavelengths of light, though there is a large overlap.  Your visual cortex takes the combined response of the three types of cones and makes up the blended color in your mind.  Magenta for example is an imaginary color.  It's the color your brain makes up to explain why both short and long wavelengths of light are detected, but not the wavelengths in the middle.  Most colors are on the color spectrum you learned in school (Red, Orange, Yellow, Green, Blue, Indigo, Violet), and will trigger a single cone type, or two adjacent cone types.
 * '''Retina''' - the tissue that supports the rods and cones.
@@ Line 18: / Line 18: @@
 * '''Vitreous humor''' is the clear gel filling the majority of the eyeball.  It is where true [[floaters]] live.  This gel is important for helping the eye hold its shape and maintain the correct pressures inside the eye even when air pressure changes.  In adults, the gel has a complex structure, with different thicknesses in different parts.
 * '''Vitreous detachment''' is attached to the outer wall of the eye in multiple locations, but can become separated.  When separated from the retina it does not support the retina fully, and puts you at higher risk for [[retinal detachment]].  It can also leave behind a large [[floater]] that impairs vision.
+* '''Extraocular muscles''',  the six muscles that control movement of the eye and one muscle that controls eyelid elevation.
 == Axial Length ==
@@ Line 24: / Line 25: @@
 == [[wikipedia:back of the envelope|Back-of-the-envelope]] calculations ==
-We can use [[Optics related math]] and some very approximate numbers to give order-of-magnitude estimates of some of the quanties involved.
+We can use [[Optics related math]] and some very approximate numbers to give order-of-magnitude estimates of some of the quantities involved.
 To estimate the focusing power of an [[emmetropic eye]], we might take the [[axial length]] as around 2.5cm. For [[distance vision]] (parallel incident light) that number is simply the [[focal length]] of the eye at rest, giving 40 [[Diopters]]. If we take the [[near point]] as about 25cm, that requires an additional 4 dpt of focusing power from the lens.
@@ Line 34: / Line 35: @@
 ==See Also==
 * [[Duochrome Test]]
+* [https://en.wikipedia.org/wiki/Human_eye Human Eye] (Wikipedia)
 ==References==