Polymers are used in the manufacture of devices used to correct vision problems.
ID: 174818 • Letter: P
Question
Polymers are used in the manufacture of devices used to correct vision problems. These devices can be temporary and removable (e.g. contact lens) or permanent (e.g. intraocular lens). Contact lenses are placed on the outside of the eye on the cornea (see Figure 1 attached) whereas intraocular lenses are implanted within the eye replacing a diseased or damaged lens of the eye (see Figures 1 and 2 attached) (a) What are the necessary requirements for a polymer used in the creation of a contact lens? Think about the function t transmission and biocompatibility with the eye. at requirements would be the differen for a disposable contact lens versus a reusable contact lens? (b) would polymers in contact lenses be in crystalline, semi-crystalline, or amorphous structures? Why? If they posses an amorphous component, would it be above or below their glass transition temperature? How do you know? (c) Intraocular lenses are used to replace the lens of the eye opacified by disease (e.g. glaucoma or damaged by trauma. What properties required for polymers used to make intraocular lenses are similar to those required for contact lenses? What required properties are different for polymers used to make intraocular lenses in comparison to those required for contact lenses? Why are they different? IExplanation / Answer
a. polymer that used in contact lens, should have transparent, flexibility, low density, tough, unreactive to chemicals on the eye surface, easy to manufacture, hydrophilic, easy to insert or remove and clean and store.
poly(methylmethyacrylate) (PMMA) is used for reusable contact lens as it is a hard and rigid polymer and can last for years. polyacrylamide is used for disposable contact lens as they are cheaper.It also contains high water content and high water content makes lens more fragile, so they cannot use longer.
b. polymers of contact lenses are amorphous in nature. Amorphous polymers do not have a regular structure and it has intermingle polymer chains which gives better optical properties (transparent) and also greater mobility.
This polymer gives three dimensional matrix only below its transition temperature. They formed hard contact lens. For soft contact lens, the polymer is above its glass transition temperature, and typically have a relatively high water content.
c. Silicone is used for the intraocular lenses. Silicone is used for its concerning PCO blocking effect. This lens design is the preferred choice for use with preloaded injectors that allow implantation through incisions.
Intraocular lenses are used generally after removing cataract and often requires post operative treatment for the patient. Therefore, it requires some supportive materials to treat any adverse effects.