(Orthokeratology, OK lens, Orthok)
Nighttime contact lens is made of super DK (oxygen permeability) materials. When sleep, nighttime orthok contact lens will reshape cornea to correct vision. *Wearer will enjoy daytime spectacle free vision after taking off of nighttime contact lenses. According to scientific research literature, orthokeratology can retard / stop myopia progression [1]. In addition, it is also used as contact lens option for dry eye cases.
Purpose of nighttime contact lens:
1. *daytime spectacle free vision
2. retard / stop myopia progression
3. reduce contact associated dry eye symptoms
4. sport fanatics
Mechanism of Nighttime contact lens:
New generation of accelerated orthokeratology lenses are made of super-DK (oxygen permeability) materials. By use of the special contour of the back surface, nighttime contact lenses will generate capillary force and suction across the corneal surface. Then the nighttime contact lenses will mold the cornea to reduce myopia.
Effectiveness (in general):
- after 5-10min of trial, the sensation with contact lenses will usually be reduced.
- after 30min of trial, the myopia will usually be reduced by approximately -1.00D.
- after one night of wearing, the myopia will drop 30% to 50% usually.
- *Daytime spectacle free vision usually achieved after 1 week.
**Case Example 1.:
- Calvin had myopia -2.50 binocularly. Since 1o years old, he put on nighttime contact lenses (orthokeratology lenses) every night. At daytime, after removal of lenses, his residual prescription was around farsighted +0.75 to +1.00. He achieved functional vision without spectacles at daytime.
- Eight years later, he went to USA for university education. The nighttime contact lens wearing frequency was reduced to four times per week.
- At 18 years old, Calvin's myopia was right eye -2.50, left eye -2.75.
**Case Example 2.:
- Joan had myopia -3.50 binocularly. Since 13 years old, she put on nighttime contact lenses (orthokeratology lenses) every night. At daytime, after removal of lenses, his residual prescription was around farsighted +0.50 to +0.75. She achieved functional vision without spectacles at daytime.
- Five years later, she went to Australia for medical school training. The wearing frequency of nighttime contact lenses was reduced to five times per week.
- At 22 years old, Joan's myopia was maintained -3.50.
**Case Example 3.:
- June had myopia -5.00 and presbyopia (reading problem) +2.00. since 50 years old, she cannot tolerate soft contact lenses because of severe dryness.
- By use of nighttime orthokeratology lenses, she can manage her driving and reading tasks without spectacles. Her residual prescription was usually +0.25 to +0.50 for right eye and -0.75 for left eye.
- She was very happy without need of reading glasses.
**To comply with privacy regulation, the aforementioned case information was modified.
Fitting procedure (~2 hours):
1. Refraction prescription and ocular health check.
2. Assess the corneal contour and health by use of corneal topographer system.
3. Trial of orthokeratology lenses for 30 minutes.
4. Check up again after removal of orthokeratology lenses. The response of the corna to the orthokeratology lenses will be reviewed by corneal topography.
5. Order lenses oversea.
6. Wearer should have regular follow up monitored by optometrist as the following schedule.
Candidate of nighttime contact lenses:
- beyond 7 years old
- myopia less than -6.00D and astigmatism less than -2.00D.
- people with fast myopia progression
- fanatics of water sports
- people not suitable for LASIK refractive surgery
- people suffering from soft contact lens related dry eye symptoms
Pros:
1. *Usually, wearer can enjoy spectacle free daytime vision after removal of contact lenses.
2. According to scientific research literature, orthokeratology can retard the myopia progression of kids [1] 。
3. Ortho-k can reduce approximately -5.00D of myopia within two weeks. (be reminded that, the effectiveness may vary among people)
5. Avoid some problems related to conventional contact lens wearing, such as dry eye and irritation of trapped sand particles.
6. Vision correction option other than LASIK refractive surgery. No laser, no knife, no dry eye.
7. Can be stopped anytime. It is reversible. Usually, the prescription will rebound within few weeks after stop wearing of the lenses.
Cons::
1. Ortho-k is NOT a CURE for myopia. The Ortho-K effect will wear off gradually after cease of lens wear.
2. Aftercare consultations are necessary to ensure effectiveness and safety.
3. Some contact lens-related problems, such as solution sensitivity, infection, corneal epithelial trauma or ulceration may occur, though the risk of complication is very dependent on compliance.
Attention! *Daytime vision quality may be affected by various factors. Wearer may still have chance to need spectacles with low power for some visual purpose. Remember complications can happen anytime! Minimize the chance of these complications through good communication with your optometrist, strict compliance and regular aftercare consultations. Parents of children who are unable to handle their contact lenses hygienically should be prepared to do these for their children, or if not, SHOULD NOT allow their children to undergo Ortho-k usage.
1. Cho P, Cheung SW. Protective Role of Orthokeratology in Reducing Risk of Rapid Axial Elongation: A Reanalysis of Data From the ROMIO and TO-SEE Studies. Invest Ophthalmol Vis Sci 2017;58(3):1411-1416.
