Orthokeratology, or Ortho-K, is a non-surgical method for correcting vision that uses specialized, rigid contact lenses worn only during sleep. These lenses gently reshape the cornea, the clear front surface of the eye, to provide clear vision throughout the day after they are removed. Ortho-K is a temporary, reversible approach that can be highly effective for many users.
The Mechanism of Overnight Correction
Orthokeratology lenses utilize a unique “reverse geometry” design, meaning the central part of the lens is flatter than the patient’s cornea. This design creates a precise space between the lens and the eye when worn overnight. Within this space, a thin layer of tears is trapped, and the resulting hydraulic forces reshape the cornea.
The gentle pressure and fluid dynamics primarily redistribute cells in the corneal epithelium, the outermost layer of the cornea. For correcting nearsightedness (myopia), the central corneal epithelium is thinned while the mid-peripheral zone thickens. This flattening changes how light enters the eye, allowing it to focus correctly on the retina. The effect is temporary, requiring consistent nightly wear to maintain the reshaped corneal profile.
Measuring Treatment Efficacy
Orthokeratology is a successful vision correction method, especially for individuals with mild to moderate nearsightedness, up to -6.00 diopters. For these patients, the treatment is designed to achieve uncorrected visual acuity of 20/40 or better during the day. Initial vision improvement is noticeable after the first night of wear, with full correction achieved within a week of consistent use.
Correction of astigmatism is also possible, particularly with newer toric lens designs, though correction is generally limited to -1.50 diopters of corneal astigmatism. Ortho-K is widely recognized for its efficacy in slowing the progression of myopia in children. Studies indicate that Ortho-K can reduce axial elongation of the eye by a significant margin, often ranging from 32% to 55% compared to wearing single-vision spectacles.
Ideal Candidates and Contraindications
The most suitable candidates for Ortho-K are children and teenagers, as the treatment is highly effective at managing and slowing the worsening of nearsightedness during their developmental years. Adults seeking freedom from daytime corrective lenses, such as athletes or those working in dusty environments, are also good candidates if they fall within the treatable range of myopia. The procedure is best suited for those with a healthy cornea.
Contraindications
Certain pre-existing conditions or high prescriptions can make Ortho-K unsuitable. Contraindications include:
- Severe dry eye syndrome or other ocular surface abnormalities.
- Active eye infections.
- Significant corneal scarring.
- Diseases like advanced keratoconus.
Safety Profile and Maintenance Requirements
When properly managed, the safety profile of Ortho-K is comparable to, or lower than, that of long-term soft contact lens wear. The primary safety concern is the risk of microbial keratitis, a serious corneal infection associated with any overnight contact lens wear. The incidence of this infection in children wearing Ortho-K lenses is estimated to be between 5.4 and 14 cases per 10,000 patient-years.
Adverse events are directly linked to poor patient compliance with hygiene and care protocols. Patients must commit to a strict maintenance schedule, including meticulous daily cleaning, disinfection, and proper storage of the lenses. Regular follow-up appointments with an eye care professional are necessary to monitor corneal health, assess the fit of the lenses, and ensure the correction is stable.