Eye drops should not be used whilst contact lenses are in the eye (with the exception of preservative-free sodium cromoglycate or preparations indicated for moistening the eye). Many ophthalmic preparations and their preservatives (e.g. benzalkonium chloride) are absorbed by contact lenses, resulting in toxic or allergic reactions. Furthermore, contact lenses, being a foreign body, delay healing. Corneal lesions can be prevented by early treatment. Users who are allergic to pollen should avoid using contact lenses when they have eye symptoms. The use of contact lenses should also be avoided during other allergic ocular manifestations. Dry eyes are a relative contraindication to the use of contact lenses when the condition is mild; in severe cases dry eyes are an absolute contraindication. Contact lenses should not be used in a very dusty environment, or when the air is particularly dry or hot. Intensive computer work is also a relative contraindication. When swimming or diving in unclean water (e.g. swimming pool) contact lenses should not be worn (if single-use lenses are used, they should be removed immediately after swimming and replaced with a new fresh pair). Contact lenses should not be used during coughs and colds. All people using contact lenses should see an ophthalmologist regularly: young (< 20 years) patients with allergies twice a year, other users once a year. An ophthalmologist should individually ensure the suitability of continuously worn contact lenses and the regular controls during the use. Daily-wear contact lenses (interval for replacement 1–3 months) are worn for e.g. 5–6 days a week. As for continuous wear contact lenses, it is safest to wear them only for a limited number of hours per day, and they should be replaced at one-month intervals. If they are worn for longer times uninterrupted, follow-up should take place at an ophthalmologist. Regular ophthalmologic controls are needed 2 times a years in persons using continuous wear lenses.Regular use of contact lenses after refractive surgery is not recommended.Proper hand hygiene
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