Eyeballs - Revision history

Angel: /* See Also */

2022-03-02T16:35:02Z

Viceroy Sam: /* Parts of the eye */ case

2020-07-31T15:09:43Z

Parts of the eye: case

← Older revision		Revision as of 15:09, 31 July 2020
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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 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.		* '''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.		* '''Extraocular muscles''', the six muscles that control movement of the eye and one muscle that controls eyelid elevation.

	== Axial Length ==		== Axial Length ==

Viceroy Sam: /* Parts of the eye */ extraocular muscles

2020-07-31T15:07:59Z

Parts of the eye: extraocular muscles

← Older revision		Revision as of 15:07, 31 July 2020
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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 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.		* '''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 ==		== Axial Length ==

Divenal: /* Back-of-the-envelope calculations */ typo

2020-07-31T11:40:24Z

Back-of-the-envelope calculations: typo

← Older revision		Revision as of 11:40, 31 July 2020
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	== [[wikipedia:back of the envelope\|Back-of-the-envelope]] calculations ==		== [[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.		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.

Divenal: /* Parts of the eye */ update rod/cone stuff

2020-06-26T21:18:46Z

Parts of the eye: update rod/cone stuff

← Older revision		Revision as of 21:18, 26 June 2020
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	* '''Lens''' - The part that changes the focus distance of the eye		* '''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 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.		* '''Retina''' - the tissue that supports the rods and cones.

Divenal: /* Parts of the eye */ add macula and fovea

2020-06-25T10:37:10Z

Parts of the eye: add macula and fovea

← Older revision		Revision as of 10:37, 25 June 2020
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	* '''Retina''' - the tissue that supports the rods and cones.		* '''Retina''' - the tissue that supports the rods and cones.
			** '''Macula''' - a small area of the retina with a higher density of light receptors.
			** '''Fovea''' - a tiny pit in the macula with the highest density of cones, for highest resolution vision.
	* '''Choroid''' - the structure behind the sclera. It can change thickness (on a timescale of days) to make small adjustments to the [[axial length]]		* '''Choroid''' - the structure behind the sclera. It can change thickness (on a timescale of days) to make small adjustments to the [[axial length]]
	* '''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 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.

Divenal: /* Back-of-the-envelope calculations */ just link to the optics-related math page, rather than repeating the thin lens equation

2020-06-24T20:06:31Z

Back-of-the-envelope calculations: just link to the optics-related math page, rather than repeating the thin lens equation

← Older revision		Revision as of 20:06, 24 June 2020
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	== [[wikipedia:back of the envelope\|Back-of-the-envelope]] calculations ==		== [[wikipedia:back of the envelope\|Back-of-the-envelope]] calculations ==

	We can use ~~simple optics, the thin lens equation <~~math~~>\frac{1}{x} + \frac{1}{y} = \frac{1}{f}</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 quanties 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.		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.

Divenal: /* Parts of the eye */ add a picture

2020-06-24T10:02:10Z

Parts of the eye: add a picture

← Older revision		Revision as of 10:02, 24 June 2020
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	== Parts of the eye ==		== Parts of the eye ==
			[[File:Schematic diagram of the human eye en.svg\|Schematic diagram of the human eye en\|right]]
	* '''Sclera''' - The white of the eye		* '''Sclera''' - The white of the eye
	* '''Cornea''' is the clear outer layer of the eye through which you can see the [[Iris]] and [[Pupil]]. It has an [[Index of Refraction]] of 1.376<ref name="Scale Model of Eye">{{Cite web \|title=Scale Model of Eye \|url=http://hyperphysics.phy-astr.gsu.edu/hbase/vision/eyescal.html \|last=Nave \|first=R \|date=2020-05-25 \|website=HyperPhysics}}</ref>, and a curved outer surface, contributing to the [[refractive state]] of the eye. The Cornea provides about 80% of the eye's total refracting power. If you have [[LASIK]] or [[PRK]] surgery it thins the cornea to change your refractive state.		* '''Cornea''' is the clear outer layer of the eye through which you can see the [[Iris]] and [[Pupil]]. It has an [[Index of Refraction]] of 1.376<ref name="Scale Model of Eye">{{Cite web \|title=Scale Model of Eye \|url=http://hyperphysics.phy-astr.gsu.edu/hbase/vision/eyescal.html \|last=Nave \|first=R \|date=2020-05-25 \|website=HyperPhysics}}</ref>, and a curved outer surface, contributing to the [[refractive state]] of the eye. The Cornea provides about 80% of the eye's total refracting power. If you have [[LASIK]] or [[PRK]] surgery it thins the cornea to change your refractive state.
Line 15:		Line 16:
	* '''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 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.		* '''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.

	== Axial Length ==		== Axial Length ==
	The primary cause of differences in [[refractive state]] is the length of the eye, referred to as axial length, relative to the focusing power. Long eyeballs are associated with myopia, as the natural lens of the eye, even when fully relaxed, focuses light too far forward of the retina.		The primary cause of differences in [[refractive state]] is the length of the eye, referred to as axial length, relative to the focusing power. Long eyeballs are associated with myopia, as the natural lens of the eye, even when fully relaxed, focuses light too far forward of the retina.

Divenal: /* Back-of-the-envelope calculations */ link to near point

2020-06-17T08:53:51Z

Back-of-the-envelope calculations: link to near point

← Older revision		Revision as of 08:53, 17 June 2020
Line 23:		Line 23:
	We can use simple optics, the thin lens equation <math>\frac{1}{x} + \frac{1}{y} = \frac{1}{f}</math> and some very approximate numbers to give order-of-magnitude estimates of some of the quanties involved.		We can use simple optics, the thin lens equation <math>\frac{1}{x} + \frac{1}{y} = \frac{1}{f}</math> and some very approximate numbers to give order-of-magnitude estimates of some of the quanties 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.		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.

	If we now suppose that myopia is due entirely to elongation (ie the focusing power is unchanged), how much does the axial length need to increase to bring the [[blur horizon]] to 40cm ? With a 40 dpt lens and a source object at 40cm, the image would form 26.67mm from the lens, giving an estimate of elongation of 1.67mm or 6%.		If we now suppose that myopia is due entirely to elongation (ie the focusing power is unchanged), how much does the axial length need to increase to bring the [[blur horizon]] to 40cm ? With a 40 dpt lens and a source object at 40cm, the image would form 26.67mm from the lens, giving an estimate of elongation of 1.67mm or 6%.

Divenal: add choroid

2020-06-15T14:18:07Z

add choroid

← Older revision		Revision as of 14:18, 15 June 2020
Line 12:		Line 12:

	* '''Retina''' - the tissue that supports the rods and cones.		* '''Retina''' - the tissue that supports the rods and cones.
			* '''Choroid''' - the structure behind the sclera. It can change thickness (on a timescale of days) to make small adjustments to the [[axial length]]
	* '''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 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.		* '''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.

← Older revision		Revision as of 16:35, 2 March 2022
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	==See Also==		==See Also==
	* [[Duochrome Test]]		* [[Duochrome Test]]

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

	==References==		==References==