Variety of contact lenses is used to correct refractive errors. Soft Contact (hydrogel) Lenses are most often used in various types of refractive errors but they have certain disadvantages. These lenses do not permit adequate Oxygen to pass through which is essential for the health of cornea and hence they can be worn for limited hours, i.e 6 to 8 hours maximum and never while sleeping. The tear proteins get deposited on these lenses which limit their life to about a year. If worn for a prolonged period or proper measures not taken to clean the lenses, the cornea can get an ULCER which at times can result in permanent loss of vision. Disposable daily wear lenses provide a safer alternative but the cost increases significantly. Since soft contact lenses are applied after cleaning with a solution which can be the cause of mild to severe allergic conjunctivitis which can become intolerable. Soft contact lenses are not ideal in eyes with high corneal astigmatism.
Merits of soft contact lenses are that they can be dispensed over the counter or purchased online though it is not ideal. A correct curvature and power of a contact lens are determined by a contact lens specialist/ Ophthalmologist after measuring exact corneal curvature and using trial contact lens. Another merit is that these lenses can be accepted very easily since even on the first day they do not produce much discomfort. These lenses can be worn off and on without any inconvenience. The recent introduction of Toric Contact Lenses has made them more acceptable in cases of moderate corneal astigmatism.
BREATHING CONTACT LENSES-
These lenses are the one which permits a significant amount of oxygen to pass through and hence can be worn for a prolonged interval without any adverse effect on the cornea. These are of two types-
1. Semisoft or Extended Wear RGP Contact Lenses
These lenses are made up of FP 92 which is a semi-rigid soft plastic and is highly permeable to oxygen. These lenses are excellent for high refractive errors, especially in patients who have high corneal astigmatism. Even cases with irregular cornea or Keratoconus, these lenses can be accepted with rewarding results.
These lenses can only be fitted by an expert Ophthalmologist since precise measurement has to be carried out and various trial lenses have to be tried to evaluate the optimum fit. The lenses are made to measurement and the patient has to be precisely trained to fit the lenses and maintain them. As stated, the lenses can be safely worn while sleeping and there is practically no danger of corneal toxicity or infection. These lenses may last for 4-5 years. One of the demerits of these lenses is that they take 5-6 days to adopt and the patient is advised to use them regularly. They are an excellent alternative to LASIK surgery.
2. SILICON HYDROGEL CONTACT LENSES
These are a recent introduction of extended wear contact lenses with the capacity to 'breathe' better than soft or hydrogel contact lenses. Some of the recent Silicon Hydrogel Contact lenses introduced by Alcon and Bausch and Lomb can be worn for a week or so.
Silicon hydrogel lenses though indicated for prolonged wear but can cause mild keratitis and sometimes allergic keratitis if worn overnight. These lenses still need a lot of improvement to be free of complications
Advise: It is ideal to consult an Ophthalmologist specialized in contact lenses for the fitting of proper contact lenses. Advertised lenses some time misguide and can be damaging to the eye.