eye disorders
Contact Lenses
Soft Hydrophilic Contact Lenses
Soft contact lenses are made of poly-2-hydroxyethyl methacrylate and other flexible plastics (such as silicone hydrogels) and are 30 to 79% water. They are 13 to 15 mm in diameter and cover the entire cornea. Soft contact lenses are often replaced daily (disposable single-use), every 2 weeks, or monthly. Soft contact lenses can improve vision in people with myopia and hyperopia. Because soft contact lenses mold to the existing corneal curvature, anything greater than minimal astigmatism cannot be treated unless a special toric lens, which has different curvatures molded onto the front lens surface, is used. Weighting the lower aspect of the toric lens maintains its orientation by reducing lens spinning. Soft contact lenses are also prescribed for treatment of corneal abrasion, recurrent erosions, or other corneal disorders (called bandage or therapeutic contact lenses). Prophylactic antibiotic eye drops (eg, fluoroquinolone 4 times a day) may be advisable with a bandage lens. Extended wearing of soft contact lenses, especially in aphakia after cataract surgery, is practical, but an ophthalmologist or optometrist should examine the patient regularly. The patient should clean the lenses once a week. Because of their larger size, soft contact lenses are not as likely as rigid contact lenses to eject spontaneously and are less likely to allow foreign bodies to lodge beneath them. Immediate wearing comfort allows for a brief adaptation period. Soft contact lenses have a higher incidence of corneal infections than GPCLs, particularly when soft lenses are worn overnight. When dry, soft contact lenses are brittle and break easily. They absorb a certain amount of moisture (based on the water content) from the tear film to retain adequate shape and pliability. Therefore, patients with dry eye are usually more comfortable wearing lenses that have a low water content. 