CONTACT LENSES - howMed Lectures -Medical Lectures and 隐形眼镜的howmed医学讲座，讲座.pptVIP

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CONTACT LENSES - howMed Lectures -Medical Lectures and 隐形眼镜的howmed医学讲座，讲座.ppt

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CONTACT LENSES - howMed Lectures -Medical Lectures and 隐形眼镜的howmed医学讲座，讲座

Commonest and earliest corneal change Occurs due to hypoxia of corneal epithelium.This occurs when lenses with poor oxygen transmission are worn overnight. Under the closed-eye sleeping conditions, oxygen availability is decreased to a level where endothelial cell dysfunction occurs leading initially to stromal than epitelial edema , finally bullae formation occurs * is more common in patients wearing soft lenses . Immunological origin in which contact lens deposits esp protiens act as allergens. * Ch hypoxia , tight or thick lens. Doesnot extend beyond 2 – 3mm If severe short course of steroids * The pattern of causal organisms is slightly different in contact lens wearers. There are relatively more Gram negative organisms, which reflects the alteration in commensal populations in contact lens wearers which, inturn, is due to the watery extraocular environment in which contact lenses are maintained. For the same reason, contact lens wearers are more susceptible to acanthamoeba keratitis * CONTACT LENSES CONTACT LENSES CONTACT LENSES Optical devices placed directly in front and adjacent to cornea To rectify refractive errors To provide protection To improve cosmetics CLASSIFICATION OF CONTACT LENSES Anatomical position Scleral contact lenses Semi-scleral contact lenses Corneal contact lenses Nature of material Rigid non-gas permeable contact lenses(PMMA) Rigid gas permeable contact lenses(CAB) Soft contact lenses(HEMA) Mode of wear Daily wear contact lenses(hard contact lenses) Extended wear contact lenses(soft contact lenses) Disposable contact lenses CLASSIFICATION OF CONTACT LENSES FDA contact lens classification Group 1 – Low water content (50%),nonionic polymers Group 2- high water content(50%),nonionic polymers Group 3- low water content(50%),ionic polymers Group 4- high water content(50%),ionic polymers Refractive correction Spherical contact lenses Toric contact lenses Bifocal contact lenses(annular,segmental,diffractive,aspheric) Color G