RIGID GAS PERMEABLE LENSES
Rigid contact lenses have evolved from the original hard lenses, that did not allow any oxygen through the material, to highly gas permeable lenses that allow normal corneal metabolism. Side effects caused by oxygen deprivation that many hard contact lens wearers endured from the 1970’s have been all but eliminated.
SOFT CONTACT LENSES
Soft lenses, which were introduced in the United States in 1971, have evolved from single use lenses that required complicated care systems to keep them clean and to extend their usable life, to packages of multi-lenses that make more frequent replacement feasible. Recommended replacement rates vary from quarterly to daily disposable. The use of cleaner and fresher contact lenses has greatly reduced many of the problems patients acquired from wearing old, coated lenses. These multi-packets of lenses are now available in even the most complicated of lens designs, including highly toric for astigmatism, and progressive vision lenses, incorporating reading, distance, and intermediate into one lens.
SILICON SOFT CONTACT LENSES
Recently soft lens materials have been developed that allow enough oxygen through for the cornea to function as if it did not have a contact lens on. These materials are extremely comfortable to wear, and tend not to dry out as much on the eye as earlier materials.
CARE SYSTEMS
The Food and Drug Administration, which took responsibility for soft and gas permeable lenses when they were first introduced, declared that daily cleaning and daily disinfection were necessary and required for any contact lens that would be reused.
Care has evolved from the early electrical heat disinfection units, to multi-purpose care kits that take seconds to use. There are daily disposable soft lenses available that require no care at all.
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Contact lenses are medical devices which sit on the eye, and despite all the advances in care and in materials, there is still potential for problems. Appropriate wearing schedules, proper instruction (both how and why) in lens care, and vigilant monitoring are critical to minimize the occurrence of these problems.
CORNEAL EDEMA
Swelling of the clear layer of the eye, resulting in haziness, if allowed to progress.
NEOVASCULARIZATION
Blood vessel growth into the cornea, in an attempt to help an oxygen deprived cornea. Sight threatening if allowed to advance to the central pupillary area.
GIANT PAPILLARY CONJUNCTIVITIS (GPC)
Transformation of the inner lining of the upper eyelid from smooth tissue to a bumpy, secretion laden tissue. Thought to be caused by a reaction to coatings on the contact lens.
RED EYE
Common causes: dirty, coated contact lenses; poorly fit contact lenses; damaged contact lenses; allergy; infection from bacteria or virus.
CORNEAL ULCER
The most feared and potentially sight threatening complication of contact lens wear. Ulcers that may leave permanent scarring are caused by infections, and are closely associated with overnight contact lens wear. Infections are much more common when basic contact lens care is ignored or trivialized. |
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