Skip to main content
Located on Corner of Buford and North Berkeley, Duluth, GA
Home » Ortho-K /CRT Lenses

Ortho-K /CRT Lenses



Orthokeratology (Ortho-K) is a non-surgical process where a rigid gas permeable (RGP) lens is used to gently reshape the cornea to correct for nearsightedness and lesser levels of farsightedness. As the word rigid suggests, the lens is a hard contact lens, unlike soft lenses that are more commonly worn today. Also unlike soft lenses, ortho-k lenses are worn only night.

If you know of anyone who wears soft lenses, it is a big no-no to sleep in those lenses overnight. This is due to the fact that the eyes breathe through the oxygen in the air. And when the eyelids are closed, oxygen supply is significantly reduced. When there is a chronic lack of oxygen (corneal hypoxia), the cornea begin to swell as a result. This leads to blurry vision, light sensitivity and other unpleasant symptoms. More on the differences between soft and hard contact lenses will be discussed in a later article.

So how are ortho-k lenses approved for overnight wear? Ortho-k lenses are smaller in diameter (between 8-10mm) and are more efficient at oxygen transmission. The smaller diameter also allows better tear exchange, which is another way oxygen can be delivered to the cornea.

Soft lenses, however, are between 14-16mm. Due to the larger diameter, the cornea is completely covered and tear exchange is minimal. For this reason, corneal hypoxia is much more common with soft lens over wear.


With nearsighted patients, the cornea has a higher curvature than normal. The increased curvature causes light to focus in front of the cornea as opposed to on the retina. This causes vision to be blurred in the distance. Subsequently, the myopic person has to get closer to objects in order to see them clearly.

With ortho-k, a rigid hard contact lens is used to flatten the cornea, which decreases its focusing power. Light is then focused on the retina to give a nice clear image when lenses are removed. Patients are then able to maintain clear vision throughout the day. However, once the patient no longer wears the lens at night, vision returns to baseline. Ortho-k lenses can be compared to how braces are used to straighten teeth.

Ortho-k has also been shown to prevent children’s prescription from getting worse form year to year. As myopia increases, there are number of conditions that the child can be susceptible to. These conditions include the risks of developing cataracts, retinal detachment and myopic macular degeneration.


  • Patients with active lifestyles and are hindered by glasses or soft contact lens wear.
  • Children whose prescription increases at a rapid rate year after year.
  • Patients not being able to tolerate soft contact lenses.


  • Provides clear vision throughout the day without the aid of glasses or contact lenses.
  • Can provide better vision for astigmatism than soft contacts.
  • Clear vision can be achieved in as little as a few days.
  • Excellent for athletes, especially swimmers, or any under water activities, as soft contact lenses increase chances of infection, irritation and potentially vision threatening conditions such as corneal ulcers.
  • Great alternative to LASIK for those who don’t want the risk or are not old enough for surgery.
  • Any changes to the cornea is completely reversible.
  • Lenses only need to be replaced once a year with proper care.


  • Initial adaptation to the lens is not as comfortable as soft contact lenses. However, patients do acclimate to the feeling of the lens in about 1 week.
  • Can only correct myopia less than -6.00 and astigmatism level of -1.75 or below.
  • Must continue to wear lenses at night in order to maintain clear vision during the day.
  • Infections: this risk is especially concerning for children and adolescents, who may be less able than compared to adults due to maintaining good hand and contact lens hygiene. However, with close parental supervision, infection rates are low.

If you feel ortho-keratology may be the right option for you, please contact our office at via the form below to schedule a consultation with us.

Schedule an Appointment
Call Our Practice