Limits of refraction correction were covered in detail in an earlier blog where I made a case for accepting -4.50D with up to -1.50D of astigmatism as the upper limit on the basis that, while not guaranteeing success, you would be likely to achieve a good outcome. Through accepting a normal distribution for describing the maximum possible change from OrthoK in a population it follows that the likelihood of achieving success increases as lower amounts of myopia are targeted. There is also a lower limit, as while it is technically possible to correct right down to -0.25, achieving a successful outcome again becomes more difficult because the OrthoK lens ultimately ends up becoming closer to an alignment fit standard rigid lens with reducing targeted correction. Accepting this argument, the limits I suggest that you accept will depend on your level of experience:
When starting out
There is no data to support my suggestion, but I’m going to advise that you consider -1.00D as the lowest amount of myopia to consider correcting with OrthoK while you are a beginner. Purely because it will make it easier for you to classify post wear topography patterns and will simplify the whole fitting process. At the upper end of the scale, I suggest you set an initial limit of -2.50D for your first few patients - again this is just to make things simpler as you would be pretty unlucky not to be successful in achieving this amount of change. Getting a few successes under your belt will provide you with a great base to work up from.
Once more experienced
With a few runs on the board, you can start pushing the limits beyond -4.50D and in the opposite direction into hyperopia as long as you accept (and warn your patient) that likelihood of success reduces the further you pass the safe limits described above. The main unknown being the maximum effect that is possible in a given individual. Lens designs that target higher refraction typically include modifications that have been designed to induce greater amounts of corneal flattening (or steepening for hyperopia). However, regardless of design, they can only achieve refractive change up to what the patients anterior corneal surface is capable of providing.
We don’t really know why, but for some reason, younger eyes respond better to OrthoK wear. In a study published in 2005, Jayakumar and Swarbrick reported reduced or delayed response to OrthoK wear in older adults aged 36yrs and above compared to younger people, with evidence of a reduced epithelial response in this older group.1 This doesn’t mean that you shouldn’t fit older people, just that it might take more time to get a good effect, so when you start out I suggest you stick to younger people as you gain confidence.
The professional time taken to fit OrthoK lenses is more extensive than fitting standard soft or rigid contact lenses, and the lenses themselves are generally more expensive than soft lenses, which makes OrthoK relatively expensive up front. But once the full correction is achieved and is stable, there are less ongoing costs than soft contact lenses that require more frequent replacement. In this regard, OrthoK is an investment that pays dividends in reduced upkeep over time. While cost is not a physical limitation to lens wear, if your patient can’t afford the upfront costs then it may as well be and so needs to be considered. There are several ways around this problem though, like spreading payments into regular direct debit amounts that might work in your location, which will be covered in a later section.
The same limitations apply here as to normal CL fitting, which means you need to perform a thorough slit-lamp investigation to rule out any anterior eye disease. No signs of eye infection, uveitis, lid disease. Healthy eyes only, please. That’s not to say anyone with anterior eye disease shouldn’t be fitted, you just need to fix their eye disease first.
Dry eye is the special case here as OrthoK can be a good option for dry eye sufferers who find daytime wear of contact lenses too uncomfortable. You won’t want to be fitting someone with raging dry eye, but patients with signs of mild corneal superficial punctate keratitis that can be attributed to dry eye or incomplete blinking, low tear break up time and mild meibomian gland dysfunction can make good candidates. This is because rigid lenses, once adapted to, tend to be more comfortable than soft lenses in dry eye patients, and besides the lenses are worn during sleep when you don’t generally feel anything anyway, unless dreaming about daemons, but that’s a different matter. Don’t ignore their dry eye though and keep to your usual practice of managing this condition while you progress with their OrthoK fitting. With the plethora of treatment options currently available, there’s a good case to be made that you shouldn’t ignore dry eye in anyone!
Trichiasis also needs some consideration, and by this, I don’t mean the pathological condition that needs to be treated and thus forms an immediate contraindication for fitting with OrthoK, but general in-turned eyelashes that some people suffer. On the face of it, fitting these people with OrthoK is no different to giving them glasses, as during the day their corneas will receive the same eyelash abuse in either case. But a better approach might be to fit them with soft contact lenses for daytime wear, that will have the secondary benefit of providing a barrier effect. It could also be argued that the cornea being compromised from eyelash scratching makes it more susceptible to infection, which carries greater risk in OrthoK compared to wearing glasses. Complicating all of this is the potential benefit of OrthoK for myopia control over soft lens corrections.
If you’re starting out is perhaps best to avoid fitting OrthoK in patients with in-grown eyelashes, unless just one or two that you can easily remove, and instead suggest soft contact lens options. But hopefully, I have given you enough information for you to make up your own mind.
- Jayakumar J and Swarbrick HA. The effect of age on short-term orthokeratology. Optom Vis Sci 2005;82:505-11.