Cornell Study: The Human Eye Can Self-correct Some Optical Faults

[Guest guest]

This is a wonderfully groundbreaking study, and a boon to everyone who is

part of the Natural Vision Improvement movement.

 

Fran

 

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Source: Cornell University

 

http://www.sciencedaily.com/releases/2003/02/030218085515.htm

 

Date:

2003-02-18

 

The Human Eye Can Self-correct Some Optical Faults

 

ITHACA, N.Y. -- While the vision-impaired Hubble Space Telescope needed

optical doctoring from shuttle astronauts, vision researchers back on Earth

were wondering if the human eye was clever enough to fix itself. Now a

neurobiology study at Cornell University suggests that internal parts of the

eye indeed can compensate for less-than-perfect conditions in other parts --

either developmentally (during the lifetime of one individual) or

genetically (over many generations).

 

Results of the study, " Internal compensation for corneal astigmatism and

high-order aberrations of the eye, " were reported to the fourth

International Congress of Wavefront Sensing and Aberration-free Refraction

Correction, Feb. 14-16 in San Francisco, by Howard C. Howland, Jennifer E.

Kelly and Toshifumi Mihashi. Howland is a Cornell professor of neurobiology

and behavior and director of the university's Developmental Vision

Laboratory; Mihashi is the chief scientist at the research institute of the

Tokyo-based Topcon Corp., manufacturer of a wavefront analyzer used in the

study; and Kelly is a Cornell senior who used the wavefront analyzer as part

of her honors thesis by testing the vision of 20 other undergraduate

students.

 

Wavefront analysis is a recently developed technique for " seeing, " with

computer-based mathematical simulation, more precisely what the eye

perceives. A beam of harmless laser light shines through the eye's optics

(the transparent cornea, which begins to focus light, and the lens, which

completes the focusing) toward the retina, where millions of photoreceptor

cones and rods line the rear surface of the eye.

 

As the light rays are reflected back through the internal optics and exit

the eye, the wavefront analyzer measures and computes deviations from a

perfectly formed light beam or test pattern a short distance in front of the

eye. Light rays exiting an optically perfect eye should be perfectly

parallel, but irregularities in the thickness or shape of the cornea or a

less-than-perfect lens can cause the exiting light rays to become

nonparallel. A test pattern (produced by light passing though regularly

spaced lenslets to form a grid, something like the lines on graph paper)

should form a regular array of luminous points in an optically perfect eye,

but a distorted pattern can tell the wavefront analyzer a great deal about

irregularities in the cornea and lens.

 

The Cornell study, which was funded, in part, by Topcon Corp., and built

upon earlier research from Spanish colleagues, looked for ways the eye might

compensate internally for several kinds of optical faults. Among them:

 

* Corneal astigmatism, which is caused by irregularities in the topography

of the cornea and can produce a distorted image;

 

* lateral coma, a so-called high-order aberration that is caused by the line

of sight not being along the axis of symmetry of the eye and produces

comet-shaped images of points of light; and

 

* spherical aberration, also a high order aberration, is what afflicted the

Hubble Space Telescope because its main mirror was too flat on the edge.

Spherical aberration in the human eye is caused by a spherical-shaped cornea

and produces blurring of the retinal image.

 

Howland, who for more than 20 years has studied the development of vision

defects in children, has been particularly interested in the possibility of

" feedback loops " by which the brain might direct parts of the eye to change

shape and compensate for optical aberrations. Reporting on the wavefront

analysis of internal compensation, he says: " We found compensation by

internal optics for three kinds of corneal aberrations of the 12 different

aberrations we investigated. We found no evidence of developmental

compensation for spherical aberration, but we did find some evidence for

developmental compensation for corneal astigmatism. We're beginning to think

that compensation for lateral coma is genetic, not developmental. "

 

He comments that all human eyes, even those that manage to produce perfect

vision, have some deviations from the optically ideal properties in their

constituent parts. " We're talking about living, biological tissue here. The

form and function of anything that's living is a combination of its genetic

background and the environment in which it is born, grows, lives and ages, "

he says, noting that many optical aberrations become more pronounced with

advancing age.

 

" With a system as complex as vision, where so many things can go wrong, it's

a wonder we can see at all. Now we're coming to realize, " Howland says,

" that visual acuity is a result of various component parts 'wanting' to see

better, if you will. They seem to be able to sense aberrations and to change

shape and function, to some extent, to produce a better result. Some of this

compensation occurs early in life, as our visual system is developing -- and

to a lesser degree throughout our lives. Other compensations occurred long

before we were born, as our distant ancestors evolved more perfect senses.

 

" And when our eyes can't compensate internally, " the neurobiologist says,

" that's when we look to those astronauts of the medical world -- the

optometrists and ophthalmic surgeons -- to fix what nature couldn't. "

 

Editor's Note: The original news release can be found here.

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http://www.sciencedaily.com/releases/2003/02/030218085515.htm