Orthokeratology Contact Lenses Work by Flattening Front of Cornea, Not the Entire Cornea.

A contact lens technique called Orthokeratology or ortho-k brings rapid improvement in vision for nearsighted patients. Now a new study shows that Orthokeratology treatment works mainly by flattening the front of the cornea, reports a recent study, "Posterior Corneal Shape Changes in Myopic Overnight Orthokeratology," appearing in the March issue of Optometry and Vision Science.

"This study appears to show that it is only, or primarily, the very front surface layers of the cornea that are altered by Orthokeratology contact lens treatment," comments Anthony Adams, OD, PhD, Editor-in-Chief of Optometry and Vision Science. The study was performed by Jeong Ho Yoon, PhD, of University of Choonhae Health Science, Ulsan, Republic of Korea, and Helen A. Swarbick, PhD, FAAO, of University of New South Wales, Sydney, Australia.


Overnight Orthokeratology Works 
-- But How?

Orthokeratology is a clinical technique to reduce nearsightedness (myopia) using specially designed rigid contact lenses to manipulate the shape of the cornea -- the transparent front part that lets light into the eye. Dr Adams likens Orthokeratology therapy to orthodontic treatment using braces to change the alignment of the teeth.

He explains "Wearing these lenses overnight for about six hours is currently the treatment approach for most clinicians who use Orthokeratology for the temporary correction of low to moderate myopia." But it has been unclear exactly how Orthokeratology works to reduce myopia: Do the contact lenses reshape just the front surface of the cornea, or do they bend and flatten the entire cornea?

To find out, Drs Yoon and Swarbick had 18 young adults with "low" (relatively mild) myopia wear Orthokeratology lenses overnight for 14 days. Using sophisticated techniques, the researchers made detailed measurements of corneal shape and thickness before, during, and after treatment.
As in previous studies, wearing Orthokeratology contact lenses led to reduced myopia, thus improving vision. The changes were significant after the first night wearing Orthokeratology lenses, By 14 days, myopia was almost completely eliminated and the participants had near-normal uncorrected (without glasses) visual acuity.

Results 'Achieved Primarily through Remodeling of Anterior Cornea'

These changes were linked to significant flattening of the anterior (front) portion of the cornea. Like the vision changes, the change in corneal shape was significant after the first night wearing Orthokeratology lenses. Although corneal flattening continued throughout the 14-day treatment period, about 80 percent of the change occurred in the first four days.

In contrast, Orthokeratology lenses caused only a small and temporary change in the shape of the posterior (rear) cornea, and only slight thinning of the central cornea. "Overall, our results support the current hypothesis that the Orthokeratology refractive effect is achieved primarily through remodeling of the anterior corneal layers, without overall corneal bending," according to Drs Yoon and Swarbick.

Overnight Orthokeratology contact lenses provide an effective treatment for relatively mild myopia. It requires custom-made rigid contact lenses designed to accommodate the shape and desired change of the patient's eye. While Orthokeratology lenses provide an alternative to LASIK surgery for correction of myopia, the patient must continue nightly contact lens wear to maintain the improvement.

The authors hope their results "will provide a more complete picture of overall corneal changes during myopic Orthokeratology." In particular, the study demonstrates that overnight Orthokeratology lenses don't change the curvature of the posterior cornea -- "at least in the first two weeks of lens wear."

This article was republished from Science Daily http://www.sciencedaily.com/releases/2013/03/130304123124.htm

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Vitamin B-Based Treatment for Corneal Disease May Offer Some Patients a Permanent Solution

ScienceDaily (Oct. 24, 2011) - Patients in the United States who have the Cornea-damaging disease keratoconus may soon be able to benefit from a new treatment that is already proving effective in Europe and other parts of the world. The treatment, called collagen crosslinking, improved vision in almost 70 percent of patients treated for keratoconus in a recent three-year clinical trial in Milan, Italy. The treatment is in clinical trials in the United States and is likely to receive FDA approval in 2012.

The results of the Milan study are being presented Oct. 24, 2011 at the 115th Annual Meeting of the American Academy of Ophthalmology in Orlando, Florida.

In a session titled Long-term Results of Corneal Crosslinking for Keratoconus, Paolo Vinciguerra, MD will describe the treatment and three-year follow up of more than 250 keratoconus patients who received collagen crosslinking at his clinic. Sixty-eight percent of the 500 eyes treated gained significant visual acuity, with their results remaining stable at the end of the follow-up period. Patients over age 18 were most likely to improve.

In the collagen crosslinking procedure, riboflavin (vitamin B) is applied to the Cornea, which is then exposed to a specific form of ultraviolet light. Collagen fibers regenerate with new bonds forming between them, increasing Corneal stiffness and strength. The treatment also combats the causes of keratoconus, reducing the chance that it will recur. The rest of the eye receives only minimal UV exposure during treatment. Dr. Vinciguerra's new study confirms that adverse effects are rare. Previous research by his team indicated no loss of Corneal endothelial cell, a measurement used to assess the safety of Corneal treatments, in patients who received collagen crosslinking.

"For many people with keratoconus, collagen crosslinking can provide a better and more permanent solution to their vision problems," said Dr. Vinciguerra. "Given that no current treatment in use in the U.S. offers permanent correction, this effective option represents a significant advance for Corneal medicine."

One in 2,000 people in the United States and worldwide are diagnosed with keratoconus, a disease that damages the collagen fibers that form the structure of the Cornea, which is the outer surface of the eye. The Cornea's crucial task is to focus, or "refract," incoming light toward the eye's lens. To perform properly, the Cornea needs to be rounded, like the surface of a ball. As keratoconus worsens and the Cornea becomes thinner, it may bulge outward in a cone shape, causing nearsightedness and/or astigmatism, making clear vision impossible. As the number of fibers and links between them decline, the Cornea loses up to 50 percent of its normal stiffness.

Standard treatments in the U.S., such as specialized eyeglasses, contact lenses, or implanted lenses, cannot permanently correct keratoconus, and none of these treatments address the underlying causes. Severe keratoconus often requires Corneal transplant.

The 115th Annual Meeting of the American Academy of Ophthalmology is in session October 23 through 25 at the Orange County Convention Center in Orlando, Fla. It is the world's largest, most comprehensive ophthalmic education conference. Approximately 25,000 attendees and more than 500 companies gather each year to showcase the latest in ophthalmic technology, products and services. To learn more about the place Where All of Ophthalmology Meets visit www.aao.org/annual_meeting.

 

http://www.sciencedaily.com/releases/2011/10/111024084641.htm

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The above story is reprinted from materials provided by American Academy of Ophthalmology.

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Cornea Gene Discovery Reveals Why Humans See Clearly

ScienceDaily (Dec. 12, 2011) — A transparent Cornea is essential for vision, which is why the eye has evolved to nourish the Cornea without blood vessels. But for millions of people around the world, diseases of the eye or trauma spur the growth of blood vessels and can cause blindness.

A new Northwestern Medicine study has identified a gene that plays a major role in maintaining clarity of the Cornea in humans and mice -- and could possibly be used as gene therapy to treat diseases that cause blindness. The paper is published in the Proceedings of the National Academy of Sciences.

"We believe we've discovered the master regulator gene that prevents the formation of blood vessels in the eye and protects the clarity of the Cornea," said lead author Tsutomu Kume, associate professor of medicine at Northwestern University Feinberg School of Medicine and a researcher at Feinberg Cardiovascular Research Institute.

The existence of the gene, FoxC1, was previously known, but its role in maintaining a clear Cornea is a new finding. Working with a special breed of mice that are missing this gene, Kume and colleagues found abnormal vascular formations, or blood vessels, streaking their Corneas and blocking light.

When Kume discovered the Corneal blood vessels in the mutant mice, he called a collaborator at the University of Alberta in Canada, Ordan Lehmann, MD, professor of ophthalmology and medical genetics.

Lehmann found that his patients who have a single copy of this mutated FoxC1 gene -- and who have congenital glaucoma -- also have abnormal blood vessel growth in their eyes.

"The exciting thing is by showing the loss of FoxC1 causes vascularization of the Cornea, it means increasing levels of the gene might help prevent the abnormal growth of blood vessels, potentially in multiple eye disorders that cause blindness," said Lehmann, a coauthor on the paper. "That's the hope." One possible use might be in corneal transplants, he said, where the growth of new blood vessels onto the transplanted cornea is a major problem.

Kume next plans to test the gene therapy in mice to see if injecting FoxC1 inhibits the formation of blood vessels in the cornea.

The research is funded by National Institutes of Health and Canadian Institutes of Health Research.

http://www.sciencedaily.com/releases/2011/12/111212153121.htm

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The above story is reprinted from materials provided by Northwestern University. The original article was written by Marla Paul.

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