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Astigmatism

Imperial-beard — Tue, 25 Aug 2026 07:49:39 GMT

Link prescription walkthrough

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	'''Astigmatism''' is an eye condition that means you have blur in a specific direction, or [[axis]] (technically, depending on the notation used for your prescription, the axis may indicate the angle of the eye's meridian where you have the least focusing power, or the one where you have the most). Astigmatism is compensated with [[cylinder]] lenses. A cylinder lens adds power along one particular meridian of the eye.

	~~Astigmatism often reduces spontaneously as myopia is corrected.~~		== Cylinder and axis on a prescription ==
			What the cylinder and axis fields mean on an eyeglass prescription, in plain language: [https://endmyopia.org/what-do-the-numbers-on-your-eye-prescription-mean/ What do the numbers on your eye prescription mean?]
	==~~Symptoms==~~
	~~Uncorrected~~ and uncompensated astigmatism appears as ''directional blur'' or ''[[double vision]]''. [[Transient astigmatism]] also occurs when making spherical reductions. According to EM, the [[visual cortex]] compensates for irregularities in the cornea. If the [[double vision]] is just a ~~little bit, the visual cortex can learn to fuse double vision and change the compensation.~~

	~~==Understanding astigmatism~~==

	~~Astigmatism is caused by an irregularly shaped cornea or lens. The first is called corneal astigmatism, which is~~ the ~~more common form,~~ and the second is called lenticular astigmatism. "Regular" astigmatism is often described as having the cornea shaped like a rugby ball, rather than spherical like a basketball. The optics of an ''idealised'' lens of such a form would cause incoming light on different planes (corresponding to the two principal axes of the lens) to be focused at different offsets beyond the lens.

	~~[[File:Astigmatism.svg\|Astigmatism]]~~

	Most diagrams of lenses show only a single vertical plane. In the real world, of course, there is a full cone of light arriving on the lens from the source object. This diagram shows two different cross-sections through the incident cone of light, aligned with the two axes. Rays in the horizontal cross-section (which contains the stronger curve) are focused earlier - at the label 'T' (for 'Tangential'). The rays in the vertical cross-section (the 'Saggital') are focused further behind, at 'S'. The other rays around the light cone are focused at points in between the two, giving an image smeared out along the axis.

	~~===Stenopaeic slit===~~

	The Stenopaeic slit is a simple tool which can be used in diagnosis / measurement of astigmatism. It is simply a disk with a narrow slit which can be rotated to find the clearest image. By reducing light coming in the "wrong" direction, the spherical correction on ~~each axis can be measured directly.~~

	~~===Analogy with Chromatic Aberration===~~

	~~It may be simpler to picture the effect by comparing with [[Chromatic Aberration]]. In both cases,~~ an ~~extra variable means different parts of the light are focused differently.~~

	~~[[File:Chromatic aberration lens diagram.svg\|Chromatic aberration lens diagram]]~~

	~~(Unfortunately the astigmatism diagram choose red and blue the wrong way round !)~~

	* If the red light is focused on the retina, ~~the green/blue light is focused~~ in ~~front, and is blurred.~~
	* If the blue light is focused correctly, green and red are focused beyond the retina and is blurred.
	* It's not possible to get everything into focus using only spherical lenses.
	~~As a compromise, focusing the green light on the retina causes a little bit of myopic blue blur and hyperopic red blur. This corresponds to the "circle of least confusion" in astigmatism.~~

	On a prescription, there are two different conventions for specifying the cylinder. This corresponds to either quoting the spherical correction to focus red on the retina, and then the additional "minus" required to focus blue; or a spherical correction for blue, and then how much that can be reduced by for red. The average of the two, or the "spherical equivalence", is then the correction required to put green on the retina.

	~~The analogue of the Stenopaeic slit is this model is a simple coloured filter~~ : ~~by allowing only monochromatic light into the eye, the spherical correction for each colour can be measured separately.~~

	~~If the object is moved away, beyond your blur horizon, so that your eye can no longer keep the green light focused,~~
	~~all colours will suffer myopic blur, but blue will have the worst blur. This corresponds to the directional blur~~
	~~in astigmatism. Adding some spherical correction would allow you to push the green back into focus.~~

	Chromatic aberration could be treated by adding some material which applies the opposite chromatic error - bending the blue light out a bit more than the red light, to cancel the error introduced by the eye. This corresponds to cylinder correction. (But as with all analogies, it's starting to stretch a bit thin...)

	~~==Irregular Astigmatism==~~

	A real cornea, of course, doesn't conform to expectations. Being messier, it just has a bulge, which means that the image is not only smeared out along the axis, but is rotated, resulting in multiple (blurred) images being perceived on the retina.

	[~~[File:Astigmatism (Eye).png\|Astigmatism (Eye)]]~~

	~~==Childhood Astigmatism==~~
	Astigmatism in young children often changes after they reach school age.<ref>{{Cite journal \|last=Dobson \|first=V. \|last2=Fulton \|first2=A. B. \|last3=Sebris \|first3=S. L. \|date=1984-01-01 \|title=Cycloplegic refractions of infants and young children: the axis of astigmatism. \|url=https://~~iovs.arvojournals~~.org/~~article.aspx?articleid=2159731 \|journal=Investigative Ophthalmology & Visual Science \|language=en \|volume=25 \|issue=1 \|pages=83–87 \|issn=1552~~-~~5783}}</ref>~~

	~~==Reducing astigmatism==~~
	As with myopia, astigmatism should be tackled in small steps when selecting lenses for [[differential]] or [[normalized]] glasses. If only a small amount of cylinder correction is present, say 0.25 [[diopters]], the cylinder correction can be dropped, with no other changes. Otherwise, cylinder should be reduced in small increments. If sphere is being reduced, cylinder should not be changed at the same time, and conversely, if cylinder is being reduced then sphere should not be changed. The only time that both sphere and cylinder should be changed, is when converting to the spherical equivalent.

	The link between astigmatism strength and visual acuity is weak. How your eyes and [[visual cortex]] respond to astigmatism is a greater factor in visual acuity than the number of dipoters.<ref>{{Cite journal \|last=Remón \|first=Laura \|last2=Tornel \|first2=Marta \|last3=Furlan \|first3=Walter D. \|date=2006-05 \|title=Visual Acuity in Simple Myopic Astigmatism: Influence of Cylinder Axis \|url=https://journals.lww.com/optvissci/Abstract/2006/05000/Visual_Acuity_in_Simple_Myopic_Astigmatism_.11.aspx \|journal=Optometry and Vision Science \|language=en-US \|volume=83 \|issue=5 \|pages=311–315 \|doi=10.1097/01.opx.0000216099.29968.36 \|issn=1538-~~9235}}</ref> If~~ the ~~standard advice for correcting astigmatism does not work for you, you may need a more gradual reduction.~~

	~~The average person with medium~~-to-high myopia should wait until having reduced norms/diffs twice each before reducing cylinder for the first time. Then wait a minimum of 8 weeks before introducing the next spherical reduction, and wait 6 months before introducing the next cylinder reduction.

	~~Regardless of how the myope reduces their lenses, the goal of each reduction is to have a small amount of "useful blur", to be cleared up with [[active focus]] and good habits.~~

	~~===Axis===~~
	~~{{Main\|Axis}}~~
	When reducing cylinder value, you should never change the axis value if it has been consistent for some time. The axis only refers to the orientation in which the cylinder is affecting your eyes, and any reduction of cylinder will happen on this orientation.

	~~==Spherical equivalent==~~
	~~{{Main\|Diopters#Spherical Equivalent}}~~
	~~The '''spherical equivalent''' of cylinder lenses may be useful, to simplify the reduced lens path. 0.50 cylinder means the power varies from 0D on one axis to 0.5D~~ on ~~the perpendicular axis. This can be substituted by the spherical power with the averaged value of 0.25D. For example, a full prescription of "~~-~~1.00 Sphere~~ -~~1.50 Cylinder" could be converted to "~~-~~1.75 Sphere".~~

	~~A common [[reduction]] is to trade 0.5 cylinder to its spherical equivalent of 0.25 sphere (of the same sign).~~
	* For example, -~~2 sph -1 cyl (equivalently, -3 +1) is reduced to -2.25 -0.5 or -2.75 +0.5.~~

	~~The resulting spherical equivalent is not intended to compensate for the asymmetry of the lens, so it will introduce some directional blur.~~

	~~==Resources==~~

	* [[Astigmatism measurement]]
	* [https://endmyopia.org/~~the-definitive-guide-astigmatism/ EndMyopia Blog - The Definitive Guide:~~ What ~~Is Astigmatism] (2013)~~
	* [https://endmyopia.org/astigmatism-the~~-big-guide-summary/ EndMyopia Blog - Astigmatism: The Big Guide & Summary] (2021)~~
	* [https://endmyopia.org/tag/astigmatism-2/ EndMyopia Blog - all astigmatism articles]
	* [https://endmyopia.org/diy-tools-how-to-measure-your~~-astigmatism-diopters/ How To Measure Your Astigmatism Diopters]~~
	* [https://visiontools.netlify.app/ Vision tool]
	~~<!-- * [https://community.endmyopia.org/t/having-trouble-figuring-out-my-astigmatism/4843/6 Astigmatism Assasin's guide] forum access required; not a public link -->~~
	* [https://www.youtube.com/watch?~~v=KDgU4AoFsA4 Fixing Astigmatism - Jake Steiner]~~
	* [https://drboulet.com/wp-content/uploads/2016/07/Forrest-a-new-model-of-functional-astigmatism.pdf Functional astigmatism]

	~~==References==~~
	~~{{reflist}}~~

	~~[[Category:Articles]]~~
	~~[[Category:Eye conditions]~~]

Diopter

Imperial-beard — Tue, 25 Aug 2026 07:49:38 GMT

Link prescription walkthrough

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	~~#REDIRECT~~ [~~[Diopters]~~]
			== Reading your prescription ==
			How diopter figures appear on an eyeglass prescription, and how to self-measure the spherical figure with the centimeter method: [https://endmyopia.org/what-do-the-numbers-on-your-eye-prescription-mean/ What do the numbers on your eye prescription mean?]

Prescription

Imperial-beard — Tue, 25 Aug 2026 07:36:26 GMT

Add Reading the numbers section

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	~~#REDIRECT~~ [[~~Correction]~~]		== Reading the numbers ==
			A full plain-language walkthrough of the prescription fields (sphere, cylinder, axis, ADD, PD), the 1978 US FTC Eyeglass Rule that requires the prescription to be handed over free of charge, and how to self-measure the spherical number with the centimeter method: [https://endmyopia.org/what-do-the-numbers-on-your-eye-prescription-mean/ What do the numbers on your eye prescription mean?] There is also a companion video: [https://www.youtube.com/watch?v=K2pERQemeTM what the numbers on your eye prescription mean (explained by Jake Steiner)].

Bifocals

Imperial-beard — Sat, 22 Aug 2026 07:58:28 GMT

Link new Varilux entry

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	[[Category:Articles]]		[[Category:Articles]]

			== See also ==
			* [[Varilux]] , Essilor progressive lens brand: the 1959 trial data, the Minkwitz constraint, and documented fall risk.

Presbyopia

Imperial-beard — Sat, 22 Aug 2026 07:58:27 GMT

Link new Varilux entry

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	[[Category:Articles]]		[[Category:Articles]]
	[[Category:Eye conditions]]		[[Category:Eye conditions]]

			== See also ==
			* [[Varilux]] , Essilor progressive lens brand: the 1959 trial data, the Minkwitz constraint, and documented fall risk.

Varilux

Imperial-beard — Sat, 22 Aug 2026 07:57:20 GMT

Create Varilux entry: history, Minkwitz optics, documented fall risk, sources

New page

== Varilux ==

'''Varilux''' is [[Essilor]]'s progressive addition lens brand and the first commercially
successful progressive lens. It was invented by Bernard Maitenaz, patented in 1953 and launched
in May 1959. Over 700 million Varilux lenses have been sold since.

=== The 1959 trial ===

Before release, Varilux was tested on 46 people in January 1959. The recorded outcomes were
5 excellent, 29 good, 2 average and '''10 poor'''. The lens launched four months later.
Roughly 22% of the founding trial did badly, so non-adaptation was documented from the start
rather than discovered later by wearers.

=== Why the peripheral blur cannot be removed ===

The distortion at the sides of any progressive lens is a geometric consequence, not a
manufacturing defect. '''Minkwitz's theorem''' (see Sheedy & Campbell, ''Optometry and Vision
Science'', 2005) states that along the umbilical corridor of a progressive surface, unwanted
astigmatism perpendicular to the corridor increases roughly '''twice as fast''' as the mean
power increases along it.

Two consequences follow:
* A stronger reading add, or a shorter corridor, produces proportionally worse peripheral blur.
* The distortion can be '''redistributed''' across the lens surface but '''cannot be reduced'''.

This applies to every progressive lens from every manufacturer. Premium designs relocate the
distortion according to assumptions about gaze behaviour; they do not remove it.

=== Current product lines ===

The current flagship is the '''XR series''', marketed as "eye-responsive" and using three named
technologies: Nanoptix, Xtend and XR-motion. '''XR Comfort Max''' claims an extended near zone.
Older '''X series''' and '''Physio''' lines remain on sale. Street prices range from about
$139 a pair online to $700-$900 or more for XR with coatings through a retail optician.

=== Documented risks ===

* Progressive lens wearers fall at roughly twice the rate of bifocal wearers: adjusted odds
ratio '''2.23''' (Lord et al., ''Optometry and Vision Science'', 2025, n=281). Falls per person
2.31 against 1.61.
* Multifocal wearers fall about '''2.3 times''' as often as non-wearers (Lord, Dayhew & Howland,
''Journal of the American Geriatrics Society'', 2002, n=156).
* Toe clearance becomes more variable in multifocals, though the mean is unchanged
(Johnson, Buckley, Scally & Elliott, ''IOVS'', 2007).
* A randomised controlled trial found that giving single vision distance glasses to multifocal
wearers '''reduced falls in those with regular outdoor activity''', while noting the switch
'''may be harmful for low-activity wearers''' (Haran et al., ''BMJ'', 2010, n=606).
* Peripheral distortion measurably corrupts optic flow, producing a false sense of upward
self-motion on level ground (Sauer et al., ''iScience'', 2021).
* Progressive wearers develop a distinct eye-head coordination pattern, holding the eyes near
centre and turning the head instead (Rifai & Wahl, ''Journal of Vision'', 2016).

The reading segment at the bottom of the lens is focused at roughly 40 cm. Floor distance is
around 150 cm, so the part of the lens used to see the ground is out of focus for the ground.

=== The endmyopia position ===

Two pairs of [[single vision]] lenses, one for distance and a deliberately weak pair for close
work, remove the corridor, the peripheral distortion and the out-of-focus lower field entirely.
See [[Differential Glasses]] and [[Presbyopia]].

=== External links ===

* [https://endmyopia.org/varilux-lenses-review/ Varilux lenses review: what the research actually shows] (endmyopia.org)
* [https://endmyopia.org/progressive-lenses-vs-bifocal-lenses/ Bifocal lenses vs progressive lenses]
* [https://doi.org/10.5281/zenodo.21016339 EndMyopia Case Report Registry, DOI 10.5281/zenodo.21016339]

[[Category:Lenses]]
[[Category:Presbyopia]]