Orthokeratology, or orthoK, offers successful treatment of myopia to patients averse to surgery, eyeglasses or contact lenses.
Orthokeratology, which gained momentum in the “˜90s thanks to new plastics technology, is experiencing resurgence with new lens designs and improved materials. The corneal reshaping therapy, called orthoK for short, is a fitting technique that helps treat patients with mild to moderate myopia while wearing contact lenses as they sleep. The lenses gently reshape the cornea to provide clear, corrected vision when the contacts are removed. While the technique has been around for decades, it wasn’t until 2002 that a lens was approved by the FDA for overnight therapeutic use.
THE ORTHOK TIMELINE
Contact lenses were mainstreamed in the early ’60s with the introduction of polymethylmethacrylate (PMMA) lenses to market as an alternative treatment for myopia, hyperopia and astigmatism. These lenses are known historically as “hard” lenses. At the time PMMA lenses were introduced to the market, eyeglasses were the only corrective option for millions of people. A few years after the introduction of PMMA contact lenses, patients reported some interesting experiences. Some noted that they could see for a period after they removed their contact lenses without the aid of glasses. They might wear their contact lenses all day and remove them to go to a cocktail party in the evening. Doctors noted that in some cases progressive myopia slowed in people who had repeatedly, year after year, manifested increases in prescription. Doctors discovered that lenses that were fit flatter than the curvature of the cornea were the reason for both phenomena, so they started purposefully fitting the contact lenses flatter. The results were dramatic in some cases. People with generally less than a certain amount of prescription could remove lenses and see, sometimes for an entire day. The resulting corneal reshaping therapy was called orthokeratology, or orthoK for short.
One of the earliest designs for orthoK, “Orthofocus,” was created from PMMA by George Jessen, OD. While interesting and helpful for many patients, PMMA material is not permeable to oxygen, so there were some inherent risks in extending wear of these orthokeratology lenses to achieve the desired effect. Also, fitting them to reduce the patient’s ametropia was an arduous and inexact science.
In the 1970s, plastics for contact lenses were developed that were permeable to oxygen. The fluorosilicone elastomers proved safer and healthier for use as corneal refractive therapy for the eye and reduced the risks associated with orthokeratology, but fitting these lenses was still challenging for the doctors and time consuming for patients.
In the ’90s, plastics had reached new levels of oxygen permeability. These “hyper-permeable” lenses made sleeping in gas permeable contacts much safer. The lens shape known as “reverse geometry” was also developed in the ’90s. It was utilized for post-refractive surgery patients. These lens curves matched the corneal shape of the eye after refractive surgery. When applied for orthoK purposes, these lenses greatly increased the ease of fitting and success for orthokeratology patients. Combining the healthier materials with the reverse geometry dimensions, orthokeratology became mainstream. It provides excellent vision without glasses or contact lenses for thousands of people worldwide.
SAFETY AND EFFICACY OF ORTHO K
Studies have been performed that demonstrate the safety and efficacy of the procedure, and other studies have shown that orthokeratology is successful at managing myopic shift, providing the only known way of myopia control for contact lens wearers. Some of these studies include The SMART study (Stabilization of Myopia through Accelerated Reshaping Technologies), The CRAYON study, (Corneal Reshaping and Yearly Observation of Nearsightedness), The COOKI study (Children’s Overnight Orthokeratology Investigation), CANDY (Controlling Astigmatism and Nearsightedness in Developing Youth) and several others.
TODAY’S ORTHOK LENSES
The first two orthoK lenses to receive FDA approval include Paragon’s Corneal Reshaping Therapy (CRT) and Vision Shaping Treatment (VST) from Bausch + Lomb. Other brands include Emerald Lens, Siesta Lens, Dreamlens, Rinehart”“Reeves and many more.
Corneal Reshaping Therapy
Paragon CRT Contact Lenses can be fit with a 100-lens Diagnostic Dispensing System (DDS), with Paragon CRT SureFit or empirically. There are 14 base curves/treatment zones and a combination of return zone depths and landing zone angles in the 100-lens DDS.
All Paragon CRT lenses are one power (+0.50 D), one diameter (10.5 mm) and laser-marked with the exact lens parameters. Paragon is the only corneal reshaping lens with the lens parameters on each lens, according to the company. Paragon CRT has “AquaComfort” plasma treatment to enhance patient comfort and lens wettability, which is standard on all lenses. The company uses a proprietary “harmonic” front and back surface design, which makes the lens up to 30% thinner than competitors’ lenses, increasing comfort and oxygen transmissibility. Paragon CRT is manufactured with FDA-approved Paragon HDS 100 material (100 Dk).
Vision Shaping Treatment
Bausch + Lomb’s VST lenses are made of Equalens II material, known for its stability and wettability. The lenses come in red and yellow tints, the red for right and yellow for left. VST represents a commercial umbrella, under which orthoK-shaping lenses can be fit using topography-based, diagnostic or empirical fitting. VST is unique in that it encompasses multiple proprietary designs, providing eyecare practitioners with fitting choices. Approved manufacturers apply their own designs (Emerald Lens, Siesta Lens, Orthofocus, etc.), making them incrementally different from one another using the basic VST platform of Equalens II above.
In our clinic we have fit orthoK for over 20 years with tremendous success and continue to promote it as a safe and effective means to control myopia with the added benefit of reducing dependence on eyeglass correction. OO
Alan Glazier, OD, is the owner and founder of Shady Grove Eye & Vision Care in Rockville, MD.
WHERE TO FIND IT:
Bausch + Lomb
800.828.9030 | bausch.com
Paragon Vision Sciences
800.528.8279 | paragonvision.com