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Contact lens has been defined as a medical device and requires a prescription from a doctor. All contact lens should maintain health and be used by the patient without the need for aide or a tool. For safety reasons, contact lens should be remove quickly if any emergency occurs. Contacts lens can be categorized by material, replacement schedule, fitment, and function.
MATERIAL
HARD CONTACT LENS VS SOFT CONTACT LENS – hard contacts are a type of contact lens with made up of a material called Poly Methyl Methacrylate and are not used today. This material did not allow enough oxygen to the cornea which lead to the development of gas permeable contact lens that contain silicone for flexibility and enhance oxygen transmissibility. Gas permeable lenses (GP) or rigid gas permeable lenses (RGP) are still in use today in various functions such as orthokeratology and the larger scleral contact lens. Soft contact lens were developed around the 1960 and comprises the majority of contact lens wear globally. Around the 1990, a newer type of soft contact lens that embedded more silicone became a new category of soft contacts called silicone hydrogels, the standard for modern contact lens.
SCHEDULE
PLANNED REPLACEMENT CONTACT LENS VS DISPOSABLE CONTACT LENS – A planned replacement lens (yearly, 6/4/3/2 month) is a contact lens that is worn multiple times before discarding. A disposable contact lens usually has a shorter schedule of wear with some being a single use contact lens. RPG lens are all planned replacement with dailies are all disposable contact lens. All the other lens fall somewhere between the two modalities.
FITMENT
LARGE VS SMALL CONTACT LENS– RGP contact lens are usually the smallest lens that only covers a portion of the cornea. They are rigid and can be constructed to a wide range of prescriptions and sizes. Scleral contact lens are the opposite in terms of fitment, they are usually the largest lens that lay on the conjunctiva vaulting of the cornea for various corneal abnormalities. Soft contact lens are made to drape over the cornea for superior comfort and fitment. They are usually available with only one diameter size with 2 curvatures. Other soft contact lenses like astigmatic contact lens tends to be bigger and thicker than spherical ones. The size of the lens can but not necessarily affect the comfort and movement of a contact lens.
FUNCTION
HEALTH VS VISION – Almost all contact lens are used to correct the refractive error of the eye but some are used as corneal bandages. When discussing vision, the prescription needs to be as accurate as possible. The other considerations that may affect your vision are the variations of soft lens material, lens design, and the type of contact lens solutions being used. Some materials and solutions can cause irritation to the eye which may affect the vision. Certain lens design can be more conducive with a patient’s prescription and cornea thus enhancing both comfort and vision. As for health, all contact lens are very healthy when used as directed. Sleeping in contact lens is usually not advisable because of the physiological changes that occur from the physical contact with the cornea, but everyone has different levels of sensitivity and resiliency hence an individual approach to fitment provides the best success. For proper maintenance of ocular health, yearly exams for contacts lens are usually mandated by law.