Talk:Accommodation (eye)

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[edit] Simplicity is better than confusion

I have taught this material to medical stduents for 30 years and I think this article will only confuse the lay person who most needs a simple, clear explanation of accommodation. Put simply, in humans, contraction of the ciliary muscle REDUCES tension on the margins of the lens allowing it to relax into a more biconvex shape changing the focal length of the lens allowing the image of the close-up object to be in focus at the level of the neural retina. —Preceding unsigned comment added by 128.143.61.114 (talk) 21:13, 26 October 2007 (UTC)

[edit] Recreation of this article

Accommodation (eye) previously redirected to Accommodation reflex. There is sufficient evidence to indicate that this article deserves to stand-alone, or even be the recipient of the redirect. First of all, given that various google searchs of "accommodation" with "lens" or "eye" reveal hits in the neighborhood of 1,200,000 to 4,250,000 whereas "accommodation reflex" gets a bit over 9,000, common usage dictates "notability" for it having its own article. Secondly, accommodation can be a voluntary process and not a reflex action. AED 08:39, 7 December 2005 (UTC)

[edit] Different theories

What is the degree of support of the various theories in current mainstream ophthamology? AxelBoldt 21:08, 17 November 2006 (UTC)

Helmholtz's theory is almost universally accepted, but Schachar's theory appears to be generating some serious interest. -AED 21:20, 17 November 2006 (UTC)
Thanks! I think it would be good to add that information to the article; it helps the reader a lot. Cheers, AxelBoldt 04:01, 18 November 2006 (UTC)

do we dont get more information about theories?

I am a lay contributor, but not only does th Schachar's theory seem barking from a mechanical point of view, the attributed reference is in fact a rebuttal of the theory. If we are going to include a reference shouldn't it be to Schirars original paper? Also having tracked down various references two of which quote that Schachar's theories have no support in the profession outside his immediate group, then wouldn't it be more appropriate to leave in but play down this section:

"Ronald Schachar has proposed (contrary to Helmholtz's theory) that the ciliary muscle actually pulls on the crystalline lens' equator in an outwardly radial manner, and the consequent changes in lens shape increase the lens power. [ref to Schachar at al. (1993) (Annals of Ophthalmology, 25 (1) 5-9)] and a derived "Scleral Expansion Band" surgical technique for the reversal of presbyopia. However, both the theory and the efficacy of the procedure has gained little support. [reference 4]"
TerryE 17:30, 2 June 2007 (UTC)
A footnote to this issue I see that Ronaldaaron (which I suspect is the given names of RA Schachar) has expanded the Schachar section, which is entirely acceptable because the published and reviewed theories have a right to be presented. However, what really worries me about these edits is that RA has also modified the Helmoltz entry to undermine its validity, even though this is the theory accepted by most ophthalmologists. To me this is crossing the bias line, and is counter to the Wikipedia guidelines. What I find mildly irritating me that in focusing on this dispute, the contributors are focusing on the area of conflict and forgetting to explain how accommodation actually works!
What I suggest is that the article should first explain how accommodation works and then present the alternative theories for how the ciliary muscle act together with zonular tension to vary the curvature of the lens. The pro RAS editors should focus on clarifying the Schachar theory (adding some paragraphing would help readability), and not undermine the counter argument. TerryE 00:19, 23 July 2007 (UTC)
[reeditted TerryE 02:00, 24 July 2007 (UTC)]

[edit] The Content of the Synopsis

Ronaldaaron (22:02, 12 July 2007) replaced the previous intro synopsis with a complete rewrite. The previous synopsis was short and specific to the main theme of this article. The new synopsis:

  • removes discussion of the cornea in accommodation mechansim
  • removes most references to the related Wikipedia pages
  • shifts the content of the paragraph to discussion of presbyopia which is already an existing article
  • is neutral to the Helmholtz / Schachar camps.

All in all I feel that the new intro is not an improvement. If we want to introduce the age dynamics of accommodation then this should be moved to a small linking section. TerryE 02:32, 24 July 2007 (UTC)

How about this:
Accommodation is the process by which the eye varies its optical power to maintain the image of an object in focus at the retina as the object varies in distance from the eye. The optical power of the eye is a result of refraction as light travels within the body of eye, with the interface between the air and the curved cornea accounting for some 45 diopters of this in the human eye, the lens and its interfaces some 20 diopters when focusing on a far object [ref to Hecht, Eugene, Optics, 2nd Ed, Addison Wesley, 1987] . Whilst the cornea is relatively rigid and therefore its power is fixed, the lens is flexible and varies in geometry due to contraction of the surrounding ciliary muscle. This ability to flex the lens is at a maximum in an infant who can add perhaps 20 diopters of optical power enabling objects less than 10 cms from the nose to be brought into focus. This declines steadily with age so that the healthy eye will typically have about 1 diopter accommodation remaining by the age of 70 years. This condition is known as presbyopia.
Given that this article is underthreat of a COI embargo I have asked for a stay until the weekend. If no one has any comments / changes, then I will swap in this intro on Sunday. At the same time I will backout AR's changes to the Helmholtz section and reinstate the pro Helmholtz references here. TerryE 19:16, 26 July 2007 (UTC)
I don't know what you imagine when you say COI "embargo". All I said at Wikipedia:Help desk#Undeleting a Deleted Article was that I might add {{COI}}. This places a template message at the top of the article to warn readers that there may be problems with the content and it can be discussed on the talk page. It does not prevent editing, and the template can be removed when the problem has been resolved. Wikipedia has many templates to tag problematic articles and it's often done. PrimeHunter 23:49, 26 July 2007 (UTC)
OK not CIO "embargo"; how about "CIO warning flag" ? TerryE 01:54, 27 July 2007 (UTC)
Yes, warning flag is a better term for it. Wikipedians usually just say "tag" about templates like this and others in Category:Neutrality templates and Category:Dispute templates. PrimeHunter 10:39, 27 July 2007 (UTC)

Hi, I did my doctoral dissertation on accommodation (I'm in a different area now), and this article doesn't reflect the subject properly. It violates both the conflict-of-interest and no-original-research rules. Essentially the article has become boilerplate from Dr. Schachar's papers. Dr. Schachar is a legitimate researcher, but his theory is by no means mainstream. I think the introduction proposed above by TerryE is a good placeholder, but that the article be rewritten to follow the standard wikipedia format, i.e. Function of Accommodation; Mechanisms of accommodation (There are at least 6 different ways to solve the focusing problem -- change lens shape, change lens distance, change retina distance, change cornea shape, etc -- and there are examples of all of them in the animal kingdom. It's fascinating.) History of accommodation research (in which Dr. Schachar will get an appropriate mention, along with Scheiner, Donders, Young, Helmholtz, Crane, Charman, etc); Neurological Aspects of Accommodation (E-W nucleus, AC/A, etc); Disorders of Accommodation (including presbyopia). Cfneveu 18:59, 25 September 2007 (UTC)

I've modified the introduction suggested above to be less anthropocentric:

Accommodation is the process by which the eye varies its optical power to maintain the image of an object in focus at the retina as the object varies in distance from the eye. There are various ways this is accomplished in vertebrate eyes:
  • Changing the shape of the lens
  • Changing the position of the lens relative to the retina
  • Changing the axial length of the eyeball.
  • Changing the shape of the cornea
Humans accommodate by changing the shape of the crystalline lens. The optical power of the eye is a result of refraction, with the interface between the air and the curved cornea accounting for some 45 diopters in the human eye, and the lens some 15 diopters when focusing on a far object [ref to Hecht, Eugene, Optics, 2nd Ed, Addison Wesley, 1987] . In humans the shape of the cornea does not change with accommodation, but the lens is flexible and varies in geometry due to contraction of the surrounding ciliary muscle. This ability to flex the lens is at a maximum in an infant who can add perhaps 20 diopters of optical power enabling objects 5 cms from the nose to be brought into focuscitation needed. This declines steadily with age so that the healthy eye will typically have about 1 diopter accommodation remaining by the age of 70 years. This condition is known as presbyopia.

Cfneveu 08:16, 1 October 2007 (UTC)