Specialty Contact Lenses

     Contact lenses have many pros and cons. For most patients  who are contact lens wearers, they find that correcting their vision with contacts is more convenient than glasses. There are many other pros of wearing contact lenses, however one of the benefits that not many are aware of is the use of contacts in management of corneal disorders. At Vespa Vision Centre, we believe in using the most up to date technologies available to us to better serve our patients. One of these technologies is in the use of specialty contact lenses.


     Patients who are affected by corneal disorders often have distorted vision that cannot be corrected well with glasses or conventional contacts. This is due to a misshapen cornea from thinning caused by degenerative corneal disorders. The most common cause is Keratoconus, however there are many other causes as well. When the cornea becomes misshapen due to thinning, a very large amount of astigmatism becomes induced because the cornea is no longer spherical. If the cornea is no longer spherical, the light is then not focused to a fine point and becomes scattered within the eye. When light is not focused to a point, the quality of vision is reduced. This astigmatism can be difficult to correct with glasses, and in some cases the reduction in vision is bad enough that they may not be legally allowed to drive. Most patients have vision in the range of 20/40 to 20/100. With a specialty contact lens, this patient may even be able to see 20/20.


    There are many kinds of specialty contact lenses, these include: Rigid Gas Permeable (RGP), thicker soft lenses, and hybrid lenses (a combination of a rigid center with a soft periphery). RGP's have been used for years, but as of recently there has been in a shift in the design of these lenses. For years the most commonly used RGP lens was a corneal lens, this implied that it would be fitted on the center of the cornea and had a smaller diameter. They provide great vision, but one noticeable downside was the issue of comfort. There was a sensation every time the patient blinked. This is in contrast to a scleral lens, a lens that vaults over the entire cornea and sits on the sclera (the white portion of the eye). While both of these lenses can provide great vision, the advantage of scleral lenses over corneal RGP's lies in comfort. This allows the patient to tolerate the lens much better, and to have longer wear time throughout the day.


     The reason these lenses provide such a vast improvement in vision over glasses and regular contacts is based on the principle of masking the misshapen surface of the cornea with a new spherical interface. When the lenses are placed on the cornea, any gaps between the cornea and the lens are filled with a tear reservoir. This results in the light coming into the eye focusing to a fine point. As mentioned before, because the light is no longer scattered, the patient is then capable of having better quality vision. See the diagrams below to view examples of corneal and scleral RGP lenses.



                                        Corneal RGP


     The RGP shown to the left is known as a lid attached fit. This is because the lens sits under the lid and the lid aids in stabilizing the position of the lens. In some patients a lid attached fit is not possible due to their lid anatomy and so a central corneal fit must be done. As mentioned before, there is a sensation on blink with this lens design but many patients can grow accustomed to this.


Source: http://webeye.ophth.uiowa.edu/eyeforum/atlas/pages/Typical-cornea-rigid-gas-permeable-contact-lens/index.htm

                                         Scleral Lens


     Scleral lenses work similarly, and as can be seen from the cross-section to the right the scleral lens vaults the entire misshapen cornea and the resulting gaps are filled with tears. This allows light to be focused more finely and results in better quality vision. The lens is also noticeably larger than the corneal lenses. As can be seen it rests on the white portion of the eye, the sclera. This results in improved comfort for the patient.

      Overall, specialty contact lenses can provide a huge change to a persons lifestyle. There are many other uses of specialty contacts than we have mentioned here. If you feel that you would benefit from these lenses or are interested in more information, you may book an appointment online with us!

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