The Effect of Ophthalmic Solutions on Contact Lenses Used After Surgery for Congenital Cataract Investigated in Vivo

Contact lenses are frequently used as a part of the treatment in professional hospital eye care with indications such as visual aid in keratokonus and scarred corneas and as bandage lenses shielding the cornea in various corneal diseases. An indication of great importance is the providing the visual correction in infants following surgery for congenital cataract. In Sweden, approximately 40 children are born with congenital cataract every year and more than 100 children develop cataract within the first years of life. The cataract can develop in one eye, unilateral cataract, or in both eyes, bilateral cataract. If the cataract is dense it is of great importance to remove the clouded lens as soon as possible to ensure the influx of light and to enable visual development. If the eye is big enough an intraocular lens (IOL) is inserted but if the eye is to small the child is left without an implanted lens. Visual development however requires not only light influx but a sharp image on the retina and to achieve good visual function contact lenses are fitted following surgery. After cataract surgery anti-inflammatory eye drops containing steroids are prescribed for several weeks and the drops are instilled in the eye with the contact lens in place.The effects of eye drops on the contact lenses and possible secondary effects on the eye are largely unknown. The ophthalmic solutions contain active ingredients as well as preservatives such as benzalkonium chloride. Benzalkonium chloride can increase the ocular permeability but also cause irritation at higher concentrations. The uptake of these substances by the lenses can impair the optical clarity of the lenses, cause discoloration, discomfort and irritate the eye. Some studies have shown accumulation of preservatives in the hydrogel contact lens matrix which could question their use in combination with ophthalmic solutions and have led to recommendations of frequent replacement of the lenses. The effects of ophthalmic solutions on the lens materials are not fully understood and most studies are performed in vitro. In collaboration with the Royal Institute of Technology (KTH) methods for measuring drug and preservative uptake by silicone hydrogel contact lenses and to study the surface morphology changes for contact lenses were developed. An in vitro model study showed that active ingredients from eye drops together with preservatives were taken up by the lenses in significant amounts. The method was further implemented in an in vivo pilot study with contact lenses collected from patients treated with different ophthalmologic preparations with the contact lens in place. No traces of active ingredients or preservatives could be found on the worn and treated lenses. The surface morphology changes were minor regardless of the time the lenses were worn or the frequency of medication, which suggests that insignificant amounts of drugs were taken up and the drugs were probably mostly removed by tear drainage. The results are presented in a manuscript that will be sent for publication.