Orthokeratology (Ortho-K) is the process by which the corneal epithelium is reshaped overnight by a gas permeable lens to provide corrected vision during the following day after the lens is removed.
The process is temporary and completely reversible. Normally it is used for the correction of myopia and minor astigmatisms, but it has also been used for the correction of small amounts of hyperopia and even presbyopia.
Myopia Control
Myopia is not just an inconvenience to be corrected by glasses or contact lenses. Higher rates of myopia can give rise to more serious pathologies, such as retinal detachment, and the trend is towards higher and higher degrees of myopia.
Over the past couple of generations, there has been a worldwide increase in the incidence and the severity of myopia (short-sightedness). In the Far East over 80% of children are now short-sighted. In the USA the rate has jumped from 25% to over 40% in a generation.
These figures are repeated around the world. Because of the rapidity of the change, it cannot be an inherited trait. It is due to environmental factors. Today’s children are spending more time than their parents and grandparents in front of computers and in artificial lighting and less time outdoors in natural daylight.
Because of the seriousness of the issue, studies are ongoing to establish the mechanisms responsible for this phenomenon, and into possible ways of controlling its progression. While no definitive cure has been found to date, some lifestyle changes can make a difference. Spending two hours each day outdoors helps, for example.
Certain contact lens modalities have been shown to slow the progression of myopia. Currently the most successful type is Ortho-Keratology (Ortho-K). An Ortho-K lens is worn overnight and removed in the morning. While sleeping, the cornea is moulded by the lens to allow the patient to see clearly throughout the following day. The peculiar shape of the image that this process forms appears to deter the eye from growing excessively, and slows the progression of the myopia.
Scleral lenses are ideal for the correction of irregularly shaped cornea, whether that irregularity has been caused by keratoconus, traumatic injury, laser surgery or a corneal graft.
Scleral lenses are large gas permeable lenses made to fit on the white part of the eye (the sclera). They are designed to vault the entire cornea, and for the weight of the lens to be borne by the white of the eye. Despite their size, scleral lenses are very comfortable.
The bowl of the lens is filled with saline or lubricating drops prior to insertion, and so the scleral lens can also provide effective relief if you suffer from dry eyes. Increasingly, scleral lenses are being used for specialist activities, such as skiing and water sports, where the risk of loss or contamination make other forms of contact lens unsuitable.
The diameter of most eyes falls within a limited range. By carefully selecting the correct base curve and diameter, a manufacturer can customise a lens design for any eye. If you are unlucky enough to fall outside of this stock size, then you may struggle to achieve the comfortable wear that most people experience.
This means that if you have an average shape and size of eye, you have a wide range of moulded products available to you. If you don’t, custom soft lenses can help. For the 20% of wearers that struggle to find a lens to fit them, a lens can be made to measure to accommodate the largest and smallest of eyes. Prescriptions can also be made to cover those unusual requirements that fall outside the standard power range, so no compromise need be made in terms of either comfort or vision.
