How the reshaping works
An ortho-k lens is a rigid gas permeable lens with an unusual back surface. A conventional GP lens is flatter at the edge than in the centre. An ortho-k lens uses reverse geometry: the zone just outside the centre is steeper than the centre itself.
Worn overnight with the eyelid closed over it, that geometry redistributes the pressure of the tear film across the corneal surface. The epithelium — the thin cell layer on the front of the cornea — gradually redistributes: slightly thinner in the centre, slightly thicker in a ring around it. The result is a flatter central cornea, which is exactly what corrects short-sightedness.
Nothing is cut and nothing is permanently altered. The epithelium is a continuously renewing tissue, which is why the effect fades when you stop.
The two reasons people are fitted
These are genuinely different goals and it is worth being clear which one applies to you.
Daytime freedom from correction. Adults with low to moderate myopia who do not want to wear glasses or daytime lenses — commonly swimmers, people in dusty or dry working environments, and people whose jobs make daytime lens wear awkward. Here ortho-k is an alternative to laser surgery that is reversible and does not involve a procedure.
Myopia control in children. Short-sightedness in children tends to progress as the eye grows longer. Ortho-k is one of the established approaches to slowing that progression, and the daytime-freedom benefit comes along with it. The measure that matters here is axial length — the physical length of the eye — rather than just the prescription, because axial length is what carries the long-term risk.
Who ortho-k suits
- Low to moderate short-sightedness. Higher prescriptions are harder to correct fully overnight, and the effect may not last a full day.
- Modest, regular astigmatism. Some designs handle more than others.
- Children in a myopia management programme, as one of several options.
- People who cannot wear lenses during the day — dusty trades, swimmers, contact sports, dry environments.
- People who want a reversible alternative to refractive surgery.
It is a poor fit if your prescription is high, if your cornea is irregular (keratoconus is not treated with ortho-k), if you have significant dry eye, or if you will not reliably keep up the hygiene routine and the follow-up visits.
The risk worth taking seriously
Sleeping in a contact lens raises the risk of microbial keratitis — a corneal infection. This is the real trade-off in ortho-k, and no honest page about it should bury the point.
What reduces the risk is unglamorous and entirely within your control:
- Wash and dry your hands before every handling of the lens.
- Use only the solutions your fitter specified. Never water, never saliva.
- Rub and rinse the lens as instructed, rather than just dropping it in solution.
- Replace the case on the schedule you were given, not when it looks dirty.
- Never top up old solution — empty, rinse and dry the case each time.
- Do not wear the lenses when you are unwell with an eye or upper respiratory infection, or if the eye is red before you go to bed.
- Attend the follow-up visits even when everything feels fine. The point of them is to find what you cannot feel.
How the fitting works
- Topography, which maps the corneal surface and drives the lens design.
- Refraction and a full eye health check, including an assessment of the tear film, since dryness affects both comfort and the reshaping.
- A diagnostic lens assessed on the eye with fluorescein, looking at the characteristic reverse-geometry pattern.
- The first overnight wear, followed by an early-morning review — often within an hour or two of lens removal, because that is when the corneal change is clearest.
- Adjustment and stabilisation over the following week or two, with further early-morning checks.
- Ongoing review at intervals your fitter sets, indefinitely, because this is a continuing treatment rather than a one-off correction.
Ortho-k against the alternatives
| Ortho-k | Daytime soft lenses | Soft multifocal (myopia control) | Laser surgery | |
|---|---|---|---|---|
| Correction during the day | No lens worn | Lens worn | Lens worn | None needed |
| Reversible | Yes | Yes | Yes | No |
| Used for myopia control | Yes | No | Yes | No |
| Suitable for children | Commonly fitted | Varies | Commonly fitted | No |
| Involves overnight wear | Yes | No | No | No |
| Main risk | Infection from overnight wear | Infection, lower | Infection, lower | Surgical and irreversible |
Questions worth asking at the fitting
- Is my prescription within the range this design corrects reliably?
- Will the effect last a full day, or should I expect it to fade by evening?
- How often will you want to see me, and for how long?
- Do you measure axial length? (Essential if this is for a child.)
- What exactly should I do if my eye is red when I wake up?