Post Refractive Contact Lenses
Despite recent advances in refractive surgical procedures, a small proportion of patients still need an optical correction after surgery in order to achieve an optimal visual result. LASIK, LASEK, PRK and other laser vision correction procedures have very high success rates and according to recent studies, more than 95% of patients who have had vision correction surgery are pleased with the results. However, a small percentage of patients remain unhappy with the visual outcome and this can happen for a number of reasons. One of the reasons is the way that individual corneas respond to laser energy and the way the healing process of the cornea takes place.
On some occasions, contact lenses may provide the only option for visual rehabilitation and restoration of binocular vision after refractive surgery. Even if patients are often disappointed with having to wear contact lenses again after they had undergone refractive surgery, correcting their vision with contacts can allow them to drive and continue their everyday activities, in many occasions even allows them to maintain employment.
With low powered induced corrections (low levels of myopia/hyperopia/astigmatism present after the surgery), where correction with glassed provides good levels of vision, conventional soft lenses are fitted in the normal way, giving a good optical result (please also see soft contact lens fitting). In cases where residual astigmatism greater than 0.75DC is present after refractive surgery, then astigmatic soft contact lenses maybe used to correct this astigmatism.
However, there are occasions where conventional soft contact lens designs do not provide a stable fit on the post refractive surgery cornea and therefore do not provide stable vision. This occurs mainly because of the difference in the shape of the central cornea, where the surgical intervention had taken place, in relation to the shape of the peripheral ‘untouched’ cornea. The greater the refractive error to be initially be corrected with the refractive surgery (eg. the greater the amount of myopia), the greater will be the difference in the geometry between the central and the peripheral cornea after the surgery. As the difference in the shape of the central and peripheral cornea increases, the contact lens fit post operatively will become less stable with conventional lenses, and that is exactly the reason why specialized contact lens designs might be required.
In high degrees of astigmatism post refractive surgery, rigid gas permeable lenses might be used in order for the best visual outcome to be achieved. Laser vision correction procedures, reshape the eye’s front surface by removing microscopic amounts of tissue from the cornea. Occasionally this can cause irregularities in the shape of the cornea that can make your vision less distinct after surgery than it was when you wore glasses or contact lenses before the surgery. These irregularities and the high astigmatism that might result after the surgery, can not be corrected with soft lenses, since soft materials conform or ‘wrap around’ the irregular cornea, only to reproduce the same distorted corneal shape at their front surface. As a result, visual distortion is reproduced at the back of the eye, resulting in a blurred image. On the contrary, gas permeable lenses are made of rigid materials and therefore maintain their shape on the eye. As a result, the space between the cornea and the back surface of a gas permeable lens is filled with tears. This reservoir of tears, covers irregularities on the corneal surface that causes distorted vision which is mainly caused by aberrations (inappropriate focusing). The front surface of the gas permeable lens, optically replaces the irregular corneal surface and therefore visual distortion is eliminated and the resulting image formed at the back of the eye, is sharp.
Following LASIK and LASEK, rigid gas permeable contact lens fitting can be done approximately 12 weeks after surgery, provided that the parameters of the cornea have stabilized. However, following PRK, this stabilization might take up to 12 months.
Patients who have undergone older refractive procedures in the past, like surgical radial keratotomies, may present to optometrists with slowly progressing corneal ectasias, usually present in both eyes. This actually means that the shape of the cornea gradually ‘collapses’ leading to distorted and reduced vision, sometimes reported by the patient, years after the surgical procedure actually took place. These cases can be complex to deal with but can be managed with different kinds of specialized contact lenses (please see specialized contact lens page).
Because of the complexities encountered when fitting post refractive corneas, gas permeable contact lens fitting after refractive surgery, are typically more complicated and more time consuming. Modified gas permeable designs, especially designed for the geometry of such eyes, will be selected carefully by your optometrist. Several lens modifications maybe required to achieve the optimum fit, comfort and desired visual outcome. If you are a post refractive surgery patient who needs to be fitted with contact lenses, it is important to know that it is best to be taken care of by an optometrist with special skills in fitting contact lenses on irregular shaped corneas. Moreover, remember that if you have never used, the specialized type of contact lens that has been selected for you post operatively, this may take longer to adapt to and it’s best to follow your optometrist guidelines concerning the caring of your new lenses, the wearing time schedule and the frequency of your contact lens aftercare visits.