![]() Because of the high water content, they have a low refractive index. With a water content of approximately 38%, they are flexible. Poly HEMA containing IOLs are also called hydrogels. Most hydrophilic IOLs utilize the same material as contact lenses: hydroxyethylmethacrylate (HEMA) ( Figure 4). Furthermore, depending on the side-chain chemistry, the flexible acrylic material can be made to be hydrophilic or hydrophobic. The newly formed polymers are now flexible and clear and this is the material that makes newer generation IOLs foldable. However the side chain molecules attached to the main polymer confer certain properties to the IOL. So, substituting the side chains in PMMA to hydroxyethyl or polyethyl groups alters the rigidity of the material. The rigid PMMA lens is acrylic in nature. Of these, the plate haptics have a higher tendency to decenter in eyes with defective anterior capsule. The two kinds of haptics include modified C loop and plate haptics. Silicone lenses are available in two variants depending on the type of haptics. The character of “glistening” is seen in silicone lenses as well. An important point about silicone lenses is that it has poor adhesive property and it is kept in place by the virtue of its haptics and capsule coalescence. ![]() Despite the low posterior capsular opacification (PCO) rate and the good resistance to Nd:YAG laser shots, silicone is less used today because it is not suitable for micro incision cataract surgery (MICS).Īdhesiveness is a property by which the IOL fuses with anterior and posterior capsule and hence reduces the risk of decentration. Although there are injectors available for safe and dry handling of silicone lenses, premature and abrupt opening of the lenses remains a dispute for most surgeons.Īfter implantation, the anterior capsule rim opacifies quickly, while the posterior capsule may remain clear for many years. Such lenses may require an incision of size up to 3.2 mm. ![]() Because of the low refractive index, the optics are rather thick especially for high refractive powers. The refractive index of silicone lens is between 1.41 and 1.46 and the optic diameter is 5.5–6.5 mm. This property allows a smaller incision than the IOL size. Silicone is hydrophobic, that is, it makes a contact angle of 99 0 with the water droplet on its material surface and therefore must be handled dry before implantation. The first foldable silicone IOL was implanted in human eyes in the 1978 by Kai-yi Zhou. ![]() Also, due to its excellent biocompatibility and versatile properties, desired optical clarity and specific viscosity can be attained. The malleable nature of silicone makes it chemically stable as well as imparts diverse mechanical properties. Since 1950s, silicone has been used in a variety of medical device applications including contact and intraocular lenses. This made way for the flexible and foldable breed of IOLs. However, the incision still had to be extended for implantation of the rigid IOL. The obligation of downsized incision was still amateur. This “glistening” phenomenon is rarely seen with PMMA.Īfter the advent of phacoemulsification in 1967, by Charles Kelman, the size of the incision did decrease significantly. Penetration by aqueous humor has been noted to cause small vacuoles within the lens optic. It is said to be three piece when the optics and the haptics are made from different materials and are attached together ( Figure 3). One piece variant of PMMA lens means that optics and haptics are made from a single mold of the same material. Hence PMMA is seldom used today except in developing countries due to economic reasons. Large sized incisions are associated with delayed healing and astigmatic refractive errors. An incision size of about 5.5–6 mm or a large corneoscleral tunnel is required for its implantation. They are usually single piece and have low memory haptics.ĭue to their property of rigidity, a large incision is required for its implantation. The refractive index is 1.49 and the usual optic diameter is 5–7 mm. Hydrophobic nature of PMMA lenses makes them more likely to adhere to corneal endothelial cells during insertion, thus causing potential endothelial loss. One of the first materials to be used for the purpose of intraocular lenses, polymethyl methacrylate (PMMA) is a rigid, non-foldable, hydrophobic material ( Figure 2).
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