July 01, 2011
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Study: Overnight ortho-K in children significantly reduces peripheral myopia

After 3 months, relative peripheral refraction moved from relative hyperopia to relative myopia.

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A study of 16 myopic children found that overnight wear with an orthokeratology lens in one eye for a duration of 3 months dramatically reduced myopia in the central 20-degree visual field, leaving the peripheral visual field with relative myopic defocus. The researchers noted that such changes in children are comparable to those reported among myopic adults wearing ortho-K lenses.

Helen A. Swarbrick, PhD, FAAO
Helen A. Swarbrick

“Previous studies have demonstrated that corneal reshaping through the use of overnight ortho-K lens wear can manipulate peripheral refractive defocus toward myopia in adults,” co-author Helen A. Swarbrick, PhD, FAAO, a professor at the School of Optometry and Vision Science, University of New South Wales, Sydney, Australia, said. “Our study was conducted in children and confirmed a similar effect. This was expected but is important to establish because control of myopia progression through manipulation of peripheral defocus is really more relevant for children than adults.”

The study, which was published in Optometry and Vision Science, was part of a larger study investigating the efficacy of overnight ortho-K lenses in reducing the progression of myopic refractive error in children.

“Current theories suggest that the stimulus that may guide eye growth in progressive myopia is the state of defocus on the peripheral rather than central retina,” Dr. Swarbrick told Primary Care Optometry News. “Hyperopic peripheral defocus, which is commonly found in myopic children, is believed to encourage eye growth, whereas manipulation of peripheral defocus toward myopia may reduce this stimulus and thus stabilize eye growth and myopic development.”

The 16 study children ranged in age from 11 years to 16 years (median age: 12.7 years), and the range of myopia was -0.56 D to -3.94 D. “All had demonstrated progression of their myopia over the previous year,” Dr. Swarbrick said.

In addition, the children were of East Asian ethnicity and selected for two major reasons.

“First, we know that in this population myopia is most prevalent and progressive,” she said. “Second, there are features of the East Asian eye, in particular eyelid tightness and morphometry, and corneal shape characteristics that may differ from other ethnicities. Thus, we sought to standardize and control for these potentially confounding factors in a modality such as ortho-K lenses that might be affected by these factors.”

The study design also employed a contralateral eye approach, with one eye being corrected with a conventional alignment fitting gas-permeable (GP) lens (10.6 mm TD, J-Contour, Capricornia Contact Lens, Brisbane), while the other eye was corrected using an overnight ortho-K lens (BE or BE-A, Capricornia) to reshape the cornea to correct myopia, with no lens wear during the day.

“Although the two lens designs and wearing modalities were quite different, the lenses were made in the same high-Dk GP material (Boston XO2),” Dr. Swarbrick said. “This study design allowed us to directly compare changes in the peripheral refraction profile between the two eyes of the same individual.”

The eye assigned to wear the ortho-K lens was chosen by a coin toss. There was also no significant difference at baseline between the GP and ortho-K lens eyes for central refractive error or corneal topography.

“The study demonstrated that after 3 months of lens wear, relative peripheral refraction in the ortho-K lens-wearing eyes moved from relative hyperopia to relative myopia,” said Dr. Swarbrick. “This change is consistent with current theories that would suggest a consequent myopia control effect. On the other hand, there was no change in relative peripheral refraction in the conventional GP lens-wearing eyes, consistent with no effect on progression of myopia in that eye.”

Specifically, ortho-K lens wear reduced central myopia from an average of -2.37 D to -0.54 D after 3 months of wear, along with no significant change in astigmatism. “The wear of a GP lens in the other eye provided daytime correction of myopia and was simply part of this specific research study design, but would not be indicated clinically,” Dr. Swarbrick said.

Dr. Swarbrick and her colleague, Pauline Kang, BOptom, found that the use of an overnight ortho-K lens for the study “induced no adverse events in our cohort of young subjects,” Dr. Swarbrick said.

However, one adverse event was recorded in an eye wearing the conventional GP lens, due to daytime lens binding. Discontinuation of lens wear in that particular patient “led to complete recovery without sequelae,” she said.

Together with the outcomes of the main study (unpublished as yet), “these results provide evidence that the use of overnight ortho-k lenses may represent a means to limit the progression of myopic refractive error in myopic children through manipulation of the peripheral optics of the eye,” Dr. Swarbrick said.

Dr. Swarbrick also noted that the use of GP contact lenses in children “can be very successful. Only two subjects out of 32 who initially enrolled in the main study were unable to adapt to daytime GP contact lens wear,” she said. “The application of overnight ortho-K lenses in this young cohort of patients – as young as 10 years old – was very successful and trouble-free, thus suggesting that GP conventional and ortho-K lenses provide viable options for contact lens wear in children.”

Earl L. Smith, III, OD, PhD
Earl L. Smith

Earl L. Smith, III, OD, PhD, dean of the University of Houston College of Optometry, has also been conducting research in this area.

“Recently there has been a substantial amount of interest in the pattern of peripheral refraction because peripheral vision may contribute to the onset and progression of myopia,” he told PCON. “Moreover, by manipulating peripheral refraction, it may be possible to influence ocular growth and refractive development in a beneficial manner.

“In particular, several lines of evidence suggest that relative peripheral hyperopia may contribute to the genesis of myopia in children,” he continued, “and that optical correction strategies that eliminate these potentially growth stimulating peripheral signals and/or produce peripheral visual signals that normally reduce ocular growth (e.g., relative peripheral myopia) may be effective in slowing the progression of myopia.”

Dr. Smith said that, in this respect, Dr. Swarbrick’s and Dr. Kang’s research shows that, as in adults, overnight ortho-K effectively alters the pattern of peripheral refraction in children. “Specifically, in addition to optically correcting central myopia, ortho-K changes the pattern of peripheral refraction from relative hyperopia to relative myopia in adolescent myopes,” he said.

“In essence,” he added, “this paper extends the results from previous studies of adults to children and, together with recent clinical trials showing that ortho-K is effective in slowing myopia progression in children, emphasizes the need to better understand the potential beneficial role of relative peripheral myopia in controlling the progression of myopia in children.” – Bob Kronemyer

Reference:

  • Kang P, Swarbrick H. Peripheral refraction in myopic children wearing orthokeratology and gas-permeable lenses. Optom Vis Sci. 2011;88(4):476-482.

  • Earl L. Smith, III, OD, PhD, is dean and Greeman-Petty Professor at the University of Houston College of Optometry. He can be reached at (713) 743-1899; esmith@uh.edu.
  • Helen A. Swarbrick, PhD, FAAO, can be reached at School of Optometry and Vision Science, University of New South Wales, Sydney, Australia; (61) 2 9385 4373; h.swarbrick@unsw.ed.
  • Disclosures: Dr. Smith has no direct financial interest in any products mentioned in this article, nor is he a paid consultant for any companies mentioned. He holds patents on lens designs that reduce relative peripheral hyperopia. Dr. Swarbrick has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned.