Keratoconus is degenerative condition of the eye where the front transparent part of the eye -namely the cornea – becomes progressively thin and cone shaped causing varying levels of visual distortion. This is the most common corneal condition we deal with.
Other corneal conditions we come across include Keratoglobus/Pellucid Marginal degeneration as well corneas that have suffered from trauma/injury or undergone unsuccessful laser refractive surgery.
In the early stages of keratoconus glasses can correct your vision as well as ‘over the counter’ contact lenses.
However, as the condition progresses so does the shape of the cornea which means your visual needs may become complex. In simple terms glasses may become largely ineffective compared to say ‘specialist medical contact lenses’
A specialist contact lens is a lens which is individually tailored to the shape of your eye providing the best vision and comfort possible.
Crucially it is important to know specialist contact lenses will help you see better but NOT slow down or treat the progression of the Keratoconus.
It is also important to know that the process of fitting you with a specialist contact lens is not always a simple task and may require several visits to the practice as the contact lenses are adjusted to optimise the fit (comfort) and vision.
Every keratoconic patient/eye is unique and before choosing which lens option would be most suitable the following must be taken into account: allergies, medical issues, lifestyle/work information and obviously a scan or a map of your eye (Topography) will need to be taken so the size/location/severity of keratoconus can be figured out.
We use advance medical grade equipment such as the Medmont 300 Topographer and Topcon Triton OCT with anterior segment attachment to assess your eyes and the fit of the contact lens in conjunction with a Digital Slit Lamp.
So what options are available?
Customised soft contact lenses
These are usually suitable for mild to moderate keratoconus as they are comfortable/easy to adapt to and are generally made thicker than conventional soft contact lenses so that they retain their shape so as to not conform too closely to the front surface of the eye – this becomes more unavoidable the steeper your cornea becomes, which then renders soft contact lenses not as effective in terms of optimum vision. Soft lenses sit on your cornea and extend well past the limbus (the junction between the coloured and white part of your eye). Soft lenses can attract deposits from the environment via the tear film which can cause discomfort and cloudy vision, so regular planned replacement is commonplace.
Corneal RGP
These lenses are usually smaller than soft contact lenses and ideally should sit centrally on your cornea floating on a very thin layer of tears which aims to neutralise the irregularity of your keratoconic cornea. They very often provide the best level of vision for this very reason and are usually the first choice for many practitioners. These lenses can be uncomfortable to start with as they move with blinks, but a well designed lens should become more comfortable the longer you wear it. If you work in a dusty environment, the lenses can become uncomfortable if dust get in under the lens. Care should be taken in dusty environments.
Piggyback contact lens system
This system combines the comfort of a soft lens with the excellent vision of an RGP lens. The soft lens under the RGP prevents the RGP lens from scratching the cornea and helps to stabilise its movement reducing lid sensation. The soft lens is usually in the form of a daily disposable and the RGP is usually an annual lens. Modern contact lens materials mean despite wearing two lenses at the same time, oxygen getting through to the cornea is no longer an issue.
Hybrid
This lens has a RGP centre with a soft surround or ‘skirt’ joined to it. The soft skirt is designed to improve the centration of the RGP by reducing its movement and at the same time improving the overall comfort. The RGP provides the quality of the vision as in a Piggyback system. It should be noted the soft skirt may be prone to deposits so regular replacement and good contact lens cleaning is of utmost importance.
Scleral / semi scleral
These lenses are essentially large RGP lenses but vary in size depending on the intended strategy of the fit. They predominantly rest on the white of the eye which is insensitive due to the absence of nerves and are therefore are probably the more comfortable lenses on the market. The scleral lens should completely vault the cornea and is designed not to move. Scleral lenses are filled with preservative free saline before inserting on the eyes and therefore can be a challenge to learn how to insert/remove these lenses initially. The smaller scleral lenses especially are light in weight, high in oxygen transmissibility and relatively easy to maintain. Some patients may find a degree of ghosting initially with scleral lenses, but as they are customisable this can usually be minimised.