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New-concept materials may widen choice of IOLs in near future
Hydrophilic and hydrophobic acrylic lenses as well as light-filtering silicone lenses offer promising options, a surgeon says.
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New materials that are expandable, light-adjustable, thermodynamic and photochromic should increase the selection of IOLs within the next few years, according to a physician.
In the past, IOLs have been manufactured from acrylic or silicone materials. These two families of polymers encompass a wide variety of compounds, Liliana Werner, MD, PhD, director of preclinical research at the Berlin Eye Research Institute, Berlin, Germany, and associate professor at the University of Utah, Salt Lake City, said in an interview with Ocular Surgery News.
“Though we have a general formula to represent the hydrogels [hydrophilic acrylics], each lens design is made of a different copolymer, with different water content, from 18% to 38%, and refractive index, from 1.46 to 1.48,” Dr. Werner said.
Hydrophilic acrylic
A new hydrogel compound, Acryfil CQ, is a proprietary copolymer hydrophilic acrylic with very high water content, at 73%, and a bonded UV absorber.
This is the material used in the Acqua lens (Mediphacos), a new-concept expandable IOL currently available in Brazil.
“The lens is delivered in its dehydrated state, with miniaturized dimensions. It goes through a very small incision and, once implanted in the watery capsular bag environment, it rehydrates, achieving its intended size, shape and optical power,” Dr. Werner said.
Capsular dyes should never be used in conjunction with this IOL because the material absorbs the color like a sponge. The lenses have had to be explanted in the few cases in which this occurred, she said.
 The Acqua (Mediphacos) expandable IOL is implanted in its dehydrated state and expands in the eye. |
 The XACT IOL (Advanced Vision Science) — Eternity (Santen) in Japan — is made of a glistening-free hydrophobic acrylic material with a high water content. Images: Werner L |
Hydrophobic acrylics
Hydrophobic acrylics are another lens variety. Normally, hydrophobic acrylic lenses have very low water content, between 0.3% and 0.5%. However, there is one IOL, the XACT lens (Advanced Vision Science) sold as Eternity (Santen) in Japan, that is made of hydrophobic acrylic with 4% water content. The new material is licensed by Bausch + Lomb to be marketed outside Japan.
“This polymer is hydrated to equilibrium water content and then packaged in 0.9% saline solution. This special treatment makes the lens glistening-free, as proven by scientific studies,” Dr. Werner said.
Glistenings are fluid-filled microvacuoles that form within the optic when the IOL is in an aqueous environment. They are observed in all types of IOLs, but have been mainly associated with hydrophobic acrylic lenses.
The mechanism and causative factors of glistening formation have been investigated in several studies, and temperature changes seem to play a significant role.
“Water absorption rate of copolymers changes according to the temperature. If the lens is placed in warm water and the temperature is then lowered, the water inside the polymer becomes oversaturated. The water surplus gathers inside polymer voids, forming glistening,” she said.
The equilibrium water content that is achieved in the XACT IOL makes the material stable. Although hydrated, it maintains hydrophobic characteristics.
Mentak and colleagues evaluated the effect of hydration on the hydrophobicity of different hydrophobic acrylic materials by measuring the contact angles.
Contact angles for dry IOLs and for IOLs hydrated at 37°C in balanced salt solution up to 28 days were measured. All dry IOLs were hydrophobic. Four-week hydration in balanced salt solution resulted in greater surface wetability for all IOLs.
“There was only a 3° drop in contact angle for the XACT IOLs and a much greater drop, from 16° to 24°, in the other lenses. In other words, the other lenses turned to a much greater hydrophilicity, with consequent changes in surface roughness and morphology,” Dr. Werner said.
The SmartIOL (Medennium) is another lens that changes its state inside the eye. It is made of a thermodynamic hydrophobic acrylic material, packaged as a solid rod. Body temperature turns the solid into a gel-like material within 30 seconds.
“The rod is 30 mm long and 2 mm wide. After implantation it turns into a 9.5-mm wide, 2- to 4-mm thick biconvex IOL. It is a very flexible lens: If compressed, it recovers full shape rapidly. This property gives to the SmartIOL great potential for accommodation,” Dr. Werner said.
The dioptric power and final dimensions of the lens are imprinted in the material before the rod is formed.
 The thermodynamic SmartIOL (Medennium) is packaged as a solid rod that expands with body temperature. If compressed, it recovers full shape rapidly. |
 The dioptric power of the Calhoun Light Adjustable Lens is adjusted in the eye under UV light exposure. |
Light adjustable lens, light-filtering IOLs
Silicone has also shown great potential for innovative IOL concepts.
The Calhoun Light Adjustable Lens (LAL) is made of a silicone matrix polymer containing macromers and photoinitiators. These components allow the lens to absorb light and to undergo adjustable power changes.
In collaboration with Calhoun, Okihiro Nishi, MD, is currently working on an injectable material that fills the capsular bag and can be polymerized within it in one procedure.
IOLs with special blockers allow filtration of light, eliminating potentially dangerous wavelengths. The SN60AT AcrySof Natural (Alcon) has integrated yellow blue-light-filtering chromophores.
 The AcrySof Natural, with integrated yellow dye, filters blue light. |
 The SofPort AO with Violet Shield (Bausch + Lomb) provides a defense from violet light. |
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“Exposure to blue light is a contributor to AMD, according to some studies. The light transmittance of this lens mimics the protection provided by the pre-cataractous human crystalline lens,” Dr. Werner explained.
Other companies offer different options for protecting the retina, such as the SofPort AO IOL with Violet Shield by Bausch + Lomb.
“There are studies suggesting that blue light should not be blocked, as it is vital for scotopic vision, while UV radiation and violet light are phototoxic and provide negligible visual information,” she said.
The SmartYellow photochromic IOL, now Matrix Acrylic Aurium (Medennium), is made of a special hydrophobic acrylic material that is perfectly colorless when the patient is indoors, but upon exposure to UV light, the lens turns yellow.
“These technological advances seem very promising indeed. However, we should not forget that, for any new material, the assessment of long-term uveal and capsular biocompatibility is very important,” Dr. Werner said. – by Michela Cimberle
References:
- Legeais JM, Werner L, Werner LP, Renard G. Les matériaux pour implants intraoculaires. Partie III: Les implants intraoculaires acryliques souples. J Fr Ophthalmol. 2001;24:309-318.
- Mentak K, et al. Hydrophobic character and aqueous wettability of hydrophobic acrylic IOLs. Paper presented at the 26th Congress of the European Society of Cataract and Refractive Surgery; September 14, 2008; Berlin, Germany.
- Werner L, Legeais JM. Les matériaux pour implants intraoculaires. Partie I: Les implants intraoculaires en polyméthylméthacrylate et modifications de surface. J Fr Ophthalmol. 1998;21:515-524.
- Werner L, Legeais JM. Les matériaux pour implants intraoculaires. Partie II: Les implants intraoculaires souples, en silicone. J Fr Ophthalmol. 1999;22:492-501.
- Werner L, Apple DJ, Crema AS, et al. Permanent blue discoloration of a hydrogel intraocular lens by intraoperative trypan blue. J Cataract Refract Surg. 2002;28(7):1279-1286.
- Werner L, Mamalis N, Romaniv N, et al. New photochromic foldable intraocular lens: Preliminary study on feasibility and biocompatibility. J Cataract Refract Surg. 2006;32(7):1214-1221.
- Werner L. Glistenings and surface light scattering in intraocular lenses. J Cataract Refract Surg. 2010;36(8):1398-1420.
- Liliana Werner, MD, PhD, can be reached at John A. Moran Eye Center, 5th floor, 50 N. Medical Drive, Salt Lake City, UT 84132, 801-581-8136; fax: 801-581-3357; e-mail: liliana.werner@hsc.utah.edu.
