Cataract 白内障

choi

Jane E Brody, Seeing Better, Living Longer; Studies suggest that cataract surgery has benefits far beyond improved vision. New York Times, Dec 5, 2017.
https://www.nytimes.com/2017/12/ ... long-your-life.html

Excerpt in the window of print: Today the procedure is done with a local anesthetic

Quote:

"After 72 very nearsighted years, 55 of them spent wearing Coke-bottle glasses, Jane Quinn of Brooklyn, NY, is thrilled with how well she can see since having her cataracts removed last year.  'It's very liberating to be able to see without glasses,' Ms Quinn told me. * * * Most often, the artificial lenses inserted correct poor visual acuity — Ms Quinn's went from 20/200 to 20/20, her serious astigmatism [散光 in Taiwan; from Greek a- without + stigma mark/ point; causing double vision] was gone, and she now needs only drugstore reading glasses.

"They are the most frequent cause of vision loss in people over 40. * * * Cataract surgery is the most frequently performed operation in the United States, with more than three million Americans having cataracts removed each year, according to the organization Prevent Blindness America. With tiny instruments, the cloudy lens is sucked out of the eye and an artificial lens inserted in its place. After about half an hour in recovery, patients can go home.

"Although there are some risks associated with removing cataracts, 'it's probably the most successful surgery we have — it has a 98 percent success rate'

"There have also been extraordinary advances in cataract surgery since the 1980s. Earlier, the surgery was done under general anesthesia and patients spent nights in the hospital and weeks in bed recovering. Today, the procedure is done with a local anesthetic and the incisions are much smaller, often requiring no stitches. One eye is operated upon at a time, with the second one typically done about two weeks later, and recuperation is fast.  As Ms Quinn put it, the surgery 'was quick and easy — maybe five minutes'

"Specialists now also recognize the wisdom of not waiting until a cataract is 'ripe' and vision seriously diminished before urging patients to consider surgery. Dr Coleman said, 'The longer you wait, the more difficult the operation. It's easier to remove cataracts before they become too dense.'

"The artificial lenses used to replace the clouded ones now come in many varieties that can be geared to a patient's particular lifestyle, desires and medical requirements.

Note: How does a cataract operation relieve astigmatism?  By inserting a special type of artificial lens (mentioned in quotation 2; medical term: intraocular lens (IOL) ) that is toric lens. But toric lens is also used in EYEGLASSES for astigmatic parents.
(a) torus
(i) The en.wikipedia.org page for "torus" is hard to understand, which does contain a gem: "Real-world examples of toroidal objects include inner tubes."
(ii) Torus. Math Is Fun, undated
https://www.mathsisfun.com/geometry/torus.html
(iii) The www.merriam-webster.com for this noun says of its etymology: "from Latin [of the same spelling], protuberance, bulge."

(b) toric lens
https://en.wikipedia.org/wiki/Toric_lens
(i) This Wiki page is also hard to comprehend. Only view the top graph to know how a toric lens is created and reason of the name (by slicing the surface of a torus).
(ii) The takeaway is that if one looks at a toric lens from the apex toward the flat base, it is oval -- not circular.

(c) This is because the cornea of of an astigmatic patient (without cataract) is also oval, not circular, if one looks into the eye of that patient (positioned in front of teh latter, of course).
(i) LRI aka Astigmatism Correction. Florida Eye Specialist Institute, undated
http://www.floridaeyespecialistinstitute.com/services/lri/t
, whose graph shows an eyeball with cornea which is longer horizontally than vertically. (That is dramatized here. In real life, the difference -- between horizontal and vertical meridians --is tiny.)
(ii) Limbal Relaxing Incision (LRI), a kind of LASIK (laser-assisted in situ keratomileusis), also offers relief to astigmatic patient, as do glasses of toric lens.
(iii) astigmatism
https://en.wikipedia.org/wiki/Astigmatism
(section 2 Types, section 2.1 Axis of the principal meridian: With-the-rule astigmatism + Against-the-rule astigmatism + Oblique astigmatism)
(A) The three in section 2.1 describes cornea of an astigmatic patient when one looks into the eye of that patient. In oblique astigmatism, the American football is neither "lying on its side" nor "standing on its end" -- but in between.
(B) "With-the-rule astigmatism – the vertical meridian is steepest (a rugby ball or American football lying on its side)."

"Steepest" because, from the apex (of the cronea), the incline is steep going fown south or north, compared to going down east or west. Besides, the cornea is not a whoel football, but the front half.

(d) In fact cataract operation, followed by insertion of IOL of toric lens type, can not completely eliminate astigmatism in most patients -- there will be some residual astigmatism which, however, is so mild that eyeglasses with toric lens are unnecessary.

Gary Heiting, OD, Astigmatism And Cataract? A Toric IOL Can Fix Both. AllAboutVision.com, updated in September 2016.
www.allaboutvision.com/conditions/toric-iols.htm