'OK' contact lenses work by flattening front of cornea, not the entire cornea

A contact lens technique called overnight orthokeratology (OK) brings rapid improvement in vision for nearsighted patients. Now a new study shows that OK 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, official journal of the American Academy of Optometry.

"This study appears to show that it is only, or primarily, the very front surface layers of the cornea that are altered by OK contact lens treatment," comments Anthony Adams, OD, PhD, Editor-in-Chief of Optometry and . 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 , Sydney, Australia.

Overnight Orthokeratology Works—But How?

Orthokeratology is a clinical technique to reduce nearsightedness () using specially designed rigid to manipulate the shape of the cornea—the transparent front part that lets light into the eye. Dr Adams likens OK therapy to 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 OK for the temporary correction of low to moderate myopia." But it has been unclear exactly how OK 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 OK lenses overnight for 14 days. Using , the researchers made detailed measurements of corneal shape and thickness before, during, and after treatment.

As in previous studies, wearing OK contact lenses led to reduced myopia, thus improving vision. The changes were significant after the first night wearing OK 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 OK 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, OK 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 OK refractive effect is achieved primarily through remodeling of the anterior corneal layers, without overall corneal bending," according to Drs Yoon and Swarbick.

Overnight OK 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 OK 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 OK." In particular, the study demonstrates that overnight OK lenses don't change the curvature of the posterior cornea—"at least in the first two weeks of lens wear."

More information: To read the article "Posterior Corneal Shape Changes in Myopic Overnight Orthokeratology", please visit journals.lww.com/optvissci/ful… ges_in_Myopic.3.aspx

add to favorites email to friend print save as pdf

Related Stories

Soft contacts designed for cone-shaped cornea

May 17, 2007

Custom-designed contacts improved vision for subjects with keratoconic eyes and offer hope of nonsurgical treatment instead of corneal transplants. University of Rochester researchers describe the custom design techniques ...

Scleral lenses benefit patients with corneal irregularities

Oct 09, 2012

(Medical Xpress)—A UC Davis Health System Eye Center study found that scleral lenses, which rest beyond the limits of the cornea and cover the white part of the eye (sclera), were a good alternative for patients with corneal ...

Recommended for you

Vitamin D link to short-sightedness ruled out

48 minutes ago

New findings from the Children of the 90s study at the University of Bristol suggest that children with low levels of vitamin D in their blood are not at increased risk of developing myopia (short-sightedness).

Multidose eye drop approach approved by joint commission

Dec 14, 2014

(HealthDay)—A policy and procedural approach to the use of multidose eye drops has been approved by The Joint Commission and can reduce costs for patients and facilities, according to an article published ...

User comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.