**2. Materials**

#### **2.1 Biocompatibility**

The biocompatibility of a material is dependent of a biological response to a foreign body material and it depends on the design and the material of the implant. The material should be chemically inert, physically stable, noncarcinogenic, nonallergenic, capable of fabrication in the required form, and have no foreign body reaction [6]. Materials used in ophthalmology should also be optically transparent for long period of time, have a high resolving power or refractive index, and should block ultraviolet rays.

The reaction of lens epithelial cells and the capsule to IOL material and design is capsular biocompatibility. The uvea's reaction to the IOL is uveal biocompatibility [7]. During cataract surgery the blood-aqueous barrier is disrupted and proteins and cells are released in the aqueous humor. Proteins then adsorb on the IOL surface and this will influence subsequent cellular reactions on the IOL [8].

### **3. Glistenings**

Glistenings are a phenomenon caused by penetration of aqueous humor into the IOL material causing vacuole formation in the IOLs optic [9].

Glistenings are fluid-filled microvacuoles that form within the IOL optic when the lens is in an aqueous environment. They can be observed with any type of IOL more often in association with hydrophobic acrylic lenses.

Factors that may influence the formation of glistenings include IOL material, manufacturing technique and packaging and also the associated conditions of the eye-glaucoma, conditions leading to breakdown of the blood-aqueous barrier and use of ocular medications.

Some theories refer glistenings as a cavitation within the IOL from slow moving hydrophilic impurities within the IOL. An osmotic pressure difference between the aqueous solution within a cavity and the external media in which the lens is immersed leads to growth of the cavity [10].

**15**

*Intraocular Lens (IOL) Materials*

*DOI: http://dx.doi.org/10.5772/intechopen.89985*

**4. Hydrophobicity and hygroscopy**

draw water into their interior a hygroscopy.

**5. Polymethyl methacrylate**

sions used phacoemulsification.

into the vitreous [5].

**6. Silicone**

Glistening develop over time and indicate a dynamic process within the lens/eye

Hydrophobicity is a measure of material's tendency to separate itself from water. Every material has its measurable hydrophobicity that is graded using contact-angle measurements and it is a surface property [13–15]. It ranges from only a few degrees for almost perfectly hydrophilic surfaces, such as bare silica glass prepared with dangling hydroxyl groups [16] to almost 180° for super-hydrophobic surfaces [14]. Hydrophobicity is highly dependent of the material's chemistry since the oxygen– hydrogen bonds in water are highly polar. Partial electric charges on the atoms tend to be attracted to opposite charges. That way water dissolves salts and is attracted to materials that also have partially charged bonds. Polymers consist primarily of nonpolar carbon–carbon and carbon–hydrogen bonds, which is why they are not generally hydrophilic and is attracted to materials with partially charged bonds. Hygroscopy explains a material's tendency to absorb and hold water. A highly hygroscopic material draws water into itself. In ophthalmology the hydrophobicity has been used to describe both the surface and interior of IOLs. The interaction of an IOL's surface with water is a measure of hydrophobicity and the ability of IOLs to

The first IOL, implanted in 1949, was made of PMMA. There have been reports of original lenses implanted by Ridley remaining perfectly clear and centered for more than 28 years [3]. There were also reports of some spontaneous dislocations

It is a rigid, nonfoldable material with less than 1% water content and therefore hydrophobic. PMMA IOLs are usually single pieced, large and therefore nowadays rarely used. They have a refractive index of 1.49 and usual optic diameter 5–7 mm. They are s too rigid to fold and therefore the lens cannot pass through the small inci-

Silicon IOLs were designed to allow implanting through the incision smaller than the optics diameter. Implantation of silicone IOLs was introduced in 1984 [17]. Silicone is a hydrophobic material of refractive index 1.41–1.46 and the optic diameter of 5.5–6.5 mm. Models are three-piece design with PMMA, polyvinyl difluoride (PVDF) and polyamide haptics. The problem with silicone is an abrupt opening in the anterior chamber following implantation which may cause rupture of the posterior capsule. Silicone IOL-s suspected to favor bacterial adhesion and therefore having the higher risk of postoperative infections [18]. Silicone oil droplets adhere well to silicone IOL in patients with silicone oil tamponade used in retinal detachment or

Hydrophobic acrylic IOL have the highest degree of lens glistening in comparison to the silicone and the HSM-PMMA IOL 11.3–13.4 years after surgery. The HSM-PMMA IOL had almost no lens glistenings. Lens glistening do not interfere

system. Causes and long-term outcomes are not entirely clear [11].

with the dioptric power of the hydrophobic acrylic lens IOL [12].

#### *Intraocular Lens (IOL) Materials DOI: http://dx.doi.org/10.5772/intechopen.89985*

*Intraocular Lens*

Current materials used for IOL optics are of two types—acrylic and silicone. Acrylic materials can be rigid (PMMA) and foldable made of hydrophobic acrylic materials (AcrySof - Alcon Laboratories, Sensar – Advanced Medical Optics –

Each foldable acrylic lens design is made from a different copolymer acrylic with a different refractive index, glass transition temperature, water content, mechanical

Hydrophobic acrylic lenses and silicone lenses have very low water content (less than 1%). But there are hydrophobic acrylic materials with higher water content about 4% also available. Hydrophilic acrylic lenses are made from copolymers with

The first silicone material that was used in the industry of IOLs was polydimethylsiloxane, with refractive index of 1.41 while the new silicone materials have higher

Refractive index in foldable acrylics is 1.47 or greater, and for silicone lenses is lower—1.41 and higher. Therefore acrylic lenses are thinner than silicone ones with

The biocompatibility of a material is dependent of a biological response to a foreign body material and it depends on the design and the material of the implant. The material should be chemically inert, physically stable, noncarcinogenic, nonallergenic, capable of fabrication in the required form, and have no foreign body reaction [6]. Materials used in ophthalmology should also be optically transparent for long period of time, have a high resolving power or refractive index, and should

The reaction of lens epithelial cells and the capsule to IOL material and design is capsular biocompatibility. The uvea's reaction to the IOL is uveal biocompatibility [7]. During cataract surgery the blood-aqueous barrier is disrupted and proteins and cells are released in the aqueous humor. Proteins then adsorb on the IOL surface

Glistenings are a phenomenon caused by penetration of aqueous humor into the

Glistenings are fluid-filled microvacuoles that form within the IOL optic when the lens is in an aqueous environment. They can be observed with any type of IOL

Factors that may influence the formation of glistenings include IOL material, manufacturing technique and packaging and also the associated conditions of the eye-glaucoma, conditions leading to breakdown of the blood-aqueous barrier and

Some theories refer glistenings as a cavitation within the IOL from slow moving hydrophilic impurities within the IOL. An osmotic pressure difference between the aqueous solution within a cavity and the external media in which the lens is

and this will influence subsequent cellular reactions on the IOL [8].

IOL material causing vacuole formation in the IOLs optic [9].

more often in association with hydrophobic acrylic lenses.

AMO) and hydrophilic acrylics (Centerflex, Akreos).

higher water content ranging from 18 to 38%.

properties and other attributes.

refractive indexes.

**2. Materials**

**2.1 Biocompatibility**

block ultraviolet rays.

**3. Glistenings**

use of ocular medications.

immersed leads to growth of the cavity [10].

the same refractive power.

**14**

Glistening develop over time and indicate a dynamic process within the lens/eye system. Causes and long-term outcomes are not entirely clear [11].

Hydrophobic acrylic IOL have the highest degree of lens glistening in comparison to the silicone and the HSM-PMMA IOL 11.3–13.4 years after surgery. The HSM-PMMA IOL had almost no lens glistenings. Lens glistening do not interfere with the dioptric power of the hydrophobic acrylic lens IOL [12].

#### **4. Hydrophobicity and hygroscopy**

Hydrophobicity is a measure of material's tendency to separate itself from water. Every material has its measurable hydrophobicity that is graded using contact-angle measurements and it is a surface property [13–15]. It ranges from only a few degrees for almost perfectly hydrophilic surfaces, such as bare silica glass prepared with dangling hydroxyl groups [16] to almost 180° for super-hydrophobic surfaces [14].

Hydrophobicity is highly dependent of the material's chemistry since the oxygen– hydrogen bonds in water are highly polar. Partial electric charges on the atoms tend to be attracted to opposite charges. That way water dissolves salts and is attracted to materials that also have partially charged bonds. Polymers consist primarily of nonpolar carbon–carbon and carbon–hydrogen bonds, which is why they are not generally hydrophilic and is attracted to materials with partially charged bonds.

Hygroscopy explains a material's tendency to absorb and hold water. A highly hygroscopic material draws water into itself. In ophthalmology the hydrophobicity has been used to describe both the surface and interior of IOLs. The interaction of an IOL's surface with water is a measure of hydrophobicity and the ability of IOLs to draw water into their interior a hygroscopy.

## **5. Polymethyl methacrylate**

The first IOL, implanted in 1949, was made of PMMA. There have been reports of original lenses implanted by Ridley remaining perfectly clear and centered for more than 28 years [3]. There were also reports of some spontaneous dislocations into the vitreous [5].

It is a rigid, nonfoldable material with less than 1% water content and therefore hydrophobic. PMMA IOLs are usually single pieced, large and therefore nowadays rarely used. They have a refractive index of 1.49 and usual optic diameter 5–7 mm. They are s too rigid to fold and therefore the lens cannot pass through the small incisions used phacoemulsification.

### **6. Silicone**

Silicon IOLs were designed to allow implanting through the incision smaller than the optics diameter. Implantation of silicone IOLs was introduced in 1984 [17]. Silicone is a hydrophobic material of refractive index 1.41–1.46 and the optic diameter of 5.5–6.5 mm. Models are three-piece design with PMMA, polyvinyl difluoride (PVDF) and polyamide haptics. The problem with silicone is an abrupt opening in the anterior chamber following implantation which may cause rupture of the posterior capsule.

Silicone IOL-s suspected to favor bacterial adhesion and therefore having the higher risk of postoperative infections [18]. Silicone oil droplets adhere well to silicone IOL in patients with silicone oil tamponade used in retinal detachment or

#### *Intraocular Lens*

diabetic retinopathy surgery [19]. Therefore silicon IOL should not be implanted in highly myopic eyes in risk of retinal detachment.

Nowadays the silicone IOLs are less frequently used because they are not suitable for microincision cataract surgery (MICS).

There are also a light adjustable lens-two component silicone IOL where power is adjusted after implantation with UV-exposure in use [20, 21].

Glistenings can happen with silicone optics while the aqueous humor can penetrate the silicon material [12].

### **7. Hydrophobic foldable acrylic**

Acrylic hydrophobic IOLs are modern foldable IOLs most widely used nowadays. They are designed of copolymers of acrylate and methacrylate derived from PMMA. The intention of the new design is to make the IOL foldable. They can be manipulated during the surgery and always turning back to its original shape [22] in a short period of time. First implanted IOL was in year 1993. Hydrophobic Foldable Acrylic can be of three piece and one piece design, with optic diameter 5.5–7 mm, and overall length 12–13 mm, transparent or colored—yellow. Refractive index can be 1.44–1.55.

Single and multi-piece hydrophobic IOLs can be implanted through small incision, not lover than 2.2 mm and have to be positioned properly since they have low self-centering ability. PCO is significantly lower than in PMMA IOLs but generally a bit higher for hydrophobic acrylic lenses compared with silicone [23].

They have higher incidence of photopsias than other acrylic IOLs because of high refractive index and low anterior curvatures and some of them develop glistenings since some are easily penetrated by aqueous humor but are not always clinically relevant unless when are dense or multifocal [24]. New materials of IOLs are prehydrated to equilibrium and will not accept further water, they are hydrophobic with the contact angle with water that of hydrophobic acrylic and are packaged in BSS to absorb the eventual water content before implantation [25].

#### **8. Hydrophilic foldable acrylic**

Hydrophilic foldable acrylic is a combination of hydroxyethylmethacrylate (polyHEMA) and hydrophilic acrylic monomer [26] material and it was introduced in 1980 with several modifications since. The IOLs made of this materials are usually single pieced and designed for capsular bag implantation. Refractive index of the material is 1.43, with water content ranging from 18 to 34% [27, 28].

They are soft, compressible with excellent biocompatibility for its hydrophilic surface. They can be implanted through a small incisions, lower than 2 mm and therefore ideal for MICS [29]. The folding of poly-HEMA chains depends on the level of hydration, and so the physical and optical properties of the polymer change as a function of water content. As the lenses hydrate, they absorb water and become soft and transparent.

The main disadvantage is the higher rate of optic opacification than in other materials and lower resistance for capsular bag contraction [30, 31].

#### **9. The future of IOL s materials and designs**

Considering the new knowledge and technological improvements and achievements, we can expect the new materials and designs of IOLs. In order to improve

**17**

**Author details**

Samir Čanović1

\*, Suzana Konjevoda2

2 General Hospital - Zadar, University of Zadar, Zadar, Croatia

\*Address all correspondence to: suzana.konjevoda@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 General Hospital - Zadar, Zadar, Croatia

3 Clinical Hospital Center Split, Split, Croatia

provided the original work is properly cited.

, Ana Didović Pavičić1

and Robert Stanić3

*Intraocular Lens (IOL) Materials*

*DOI: http://dx.doi.org/10.5772/intechopen.89985*

materials and refractive ophthalmology.

biocompatibility and refractive quality we expect some changes in shape of the IOLs (discoid, plate-lamellar, ball shaped) and therefore some novelties in implantation possibilities. The new neuro-ophthalmological knowledge and knowledge about adaptation and perception, industries based on robotic approach and innovations give us the right to expect some new and completely different IOLs in their shape, materials and functioning principle [32, 33]. In conclusion, in the future, we can expect some new, different and innovative approaches in the IOLs design and

#### *Intraocular Lens (IOL) Materials DOI: http://dx.doi.org/10.5772/intechopen.89985*

*Intraocular Lens*

diabetic retinopathy surgery [19]. Therefore silicon IOL should not be implanted in

Nowadays the silicone IOLs are less frequently used because they are not suitable

There are also a light adjustable lens-two component silicone IOL where power is

Glistenings can happen with silicone optics while the aqueous humor can

Acrylic hydrophobic IOLs are modern foldable IOLs most widely used nowadays. They are designed of copolymers of acrylate and methacrylate derived from PMMA. The intention of the new design is to make the IOL foldable. They can be manipulated during the surgery and always turning back to its original shape [22] in a short period of time. First implanted IOL was in year 1993. Hydrophobic Foldable Acrylic can be of three piece and one piece design, with optic diameter 5.5–7 mm, and overall length 12–13 mm,

Single and multi-piece hydrophobic IOLs can be implanted through small incision, not lover than 2.2 mm and have to be positioned properly since they have low self-centering ability. PCO is significantly lower than in PMMA IOLs but generally a

They have higher incidence of photopsias than other acrylic IOLs because of high refractive index and low anterior curvatures and some of them develop glistenings since some are easily penetrated by aqueous humor but are not always clinically relevant unless when are dense or multifocal [24]. New materials of IOLs are prehydrated to equilibrium and will not accept further water, they are hydrophobic with the contact angle with water that of hydrophobic acrylic and are packaged in

Hydrophilic foldable acrylic is a combination of hydroxyethylmethacrylate (polyHEMA) and hydrophilic acrylic monomer [26] material and it was introduced in 1980 with several modifications since. The IOLs made of this materials are usually single pieced and designed for capsular bag implantation. Refractive index of

They are soft, compressible with excellent biocompatibility for its hydrophilic surface. They can be implanted through a small incisions, lower than 2 mm and therefore ideal for MICS [29]. The folding of poly-HEMA chains depends on the level of hydration, and so the physical and optical properties of the polymer change as a function of water content. As the lenses hydrate, they absorb water and become

The main disadvantage is the higher rate of optic opacification than in other

Considering the new knowledge and technological improvements and achievements, we can expect the new materials and designs of IOLs. In order to improve

the material is 1.43, with water content ranging from 18 to 34% [27, 28].

materials and lower resistance for capsular bag contraction [30, 31].

**9. The future of IOL s materials and designs**

highly myopic eyes in risk of retinal detachment.

adjusted after implantation with UV-exposure in use [20, 21].

transparent or colored—yellow. Refractive index can be 1.44–1.55.

bit higher for hydrophobic acrylic lenses compared with silicone [23].

BSS to absorb the eventual water content before implantation [25].

for microincision cataract surgery (MICS).

penetrate the silicon material [12].

**7. Hydrophobic foldable acrylic**

**8. Hydrophilic foldable acrylic**

soft and transparent.

**16**

biocompatibility and refractive quality we expect some changes in shape of the IOLs (discoid, plate-lamellar, ball shaped) and therefore some novelties in implantation possibilities. The new neuro-ophthalmological knowledge and knowledge about adaptation and perception, industries based on robotic approach and innovations give us the right to expect some new and completely different IOLs in their shape, materials and functioning principle [32, 33]. In conclusion, in the future, we can expect some new, different and innovative approaches in the IOLs design and materials and refractive ophthalmology.
