Aberropia, Corneal Onlay

Aberropia and HOA

We eyecare professionals have known for quite some time that there are more things that cause a human eye to experience blur and vision distortion than "the big 4" - myopia, hyperopia, astigmatism and presbyopia.

Currently the vast majority of vision correction in the forms of glasses, contacts and refractive procedures deals with the 3 "low order aberrations" (LOA):

1) DEFOCUS (myopia and hyperopia)
2) ASTIGMATISM
3) PRESBYOPIA (this is not really a true LOA, but since it is solvable by some of the same lenses and methods as the 1st 2, I am choosing to group them together for the purpose of this explanation)

So when your vision is blurry and you go get new glasses or contacts or LASIK, most of the time the only thing being corrected is the LOA. But just as I said earlier, thats not all that makes a human eye blurry. There are dozens more distortions of the human eye that cause blur that until recently were not easily measured in the human eye, and therefore were not correctable by any means. Some of them are: SPHERICAL ABERRATION, CHROMATIC ABERRATION, SECONDARY ASTIGMATISM, TERTIARY ASTIGMATISM, COMA and more. For the most part these are mathematically complicated distortions that traditionally have been unfixable b/c the technology was not there to produce lenses to "fit" the HOA.

Well those days are just about to be over. Multiple laser manufacturers have produced devices to correct for HOA in LASIK. At least one glasses and contact lens manufacturer (IZON) can make "super" glasses that correct for HOA. The problem now is that the technology is expensive and therefore not widely available yet. Its coming quickly, though.

Back to the original title of this entry...the new medical diagnosis of ABERROPIA. The definition is "a refractive error that results in a decrease in the visual quality that can be attributable to high order aberration". That would be optical/ocular blur that is not caused by LOA (myopia, etc), but also not attributable to eye disease (such as cataracts, retinal problems, corneal degeneration, ect).

Read more about it here:

http://www.osnsupersite.com/view.asp?rID=23161

Tags: aberropia, loa, hoa, izon | Edit Tags

Wednesday October 31, 2007 - 12:33pm (CDT) Edit | Delete | Permanent Link | 0 Comments

Corneal Onlays

Lo0king for the next big thing in vision correction? This may be it. A corneal onlay is a 6mm diameter synthetic disc about 1/2 the thickness of a piece of paper that can be placed just underneath the corneal epithelium, and is used to change overall ocular refractive error. What that means in English is basically "implantable contact lens". No muss, no fuss. No care. Just like having LASIK w/o the complications...AND its removable/replaceable to boot!

Now if you google "implantable contact lens" (ICL), you'll come up with something totally different: a "phakic IOL". Corneal onlays are totally different. A phakic IOL involves a fairly invasive surgery, and is not easily replaced.

Also don't confuse a corneal onlay with a corneal IN-lay...those are different as well. A corneal inlay must be modified by a laser (like LASIK or PRK) after insertion, and is being tested for hyperopia or farsightedness.

No, a corneal ON-lay is a different animal. This is a procedure that I personally think will be widely performed by optometrists everywhere. In Texas an optometrist can debride a cornea down to the level of Bowman's layer (a layer of the cornea). Thats all this minor procedure requires.

So: you'd go in to your optometrist's office, he or she would take some measurements, then instill an eyedrop to anesthetize (numb) your cornea. Then the doc would remove a little bit of the very top layer of your cornea and place this "corneal onlay" (in your Rx) in its spot. a bandage contact lens would be applied and they'd send you home. The next day you'd come in and the bandage contact lens would be removed...and your own cornea will have regrown over the inlay. VIOLA! Implantable contact lens. Wear it as long as you see well. Don't remove it, don't clean it, don't worry about it. If you start seeing blurry...go back and the optometrist removes it and replaces it with a stronger (or weaker) one. No lasers, no invasive surgery.

http://www.iovs.org/cgi/content/full/43/10/3196