FLEXIBLE IOLS

SILICONE

 

• Introduced in 1984 as a foldable IOL material 

• Used in order to make corneal incision size smaller during IOL implantation

• Polymers consist of silicone and oxygen

  • ​High refractive index, therefore allowing thinner IOL optics

 

 

 

• Hydrophobic

 

• Wettability angle of 99º

  • ​N.B. Wettability angle is the contact angle

between a solid and liquid

 

 

 

• IOL implantation can be difficult due to the slippery nature of silicone's surface when wet

  • ​Therefore handled dry during surgery

 

• Currently, 3-piece models are used

 

• ​With haptics made of PMMA, PVDF or Polyamide

 

 

 

 

 

 

 

• Injectors have been developed for insertion of these lenses

  • ​Allowing for easier handling

 

 

 

• When silicone IOLs are inserted into the capsular bag, they tend to unfold rapidly and uncontrollably

  • ​This increases the likelihood of intraocular damage

 

• Bacteria adhesion in these lenses has also been known

  • This has lead to an increased risk of post-surgery infection

 

 

• Once implanted, anterior capsular opacification (ACO) and inflammation occurs 

• ​Rate of ACO is higher in IOLs with a plate-haptic design 

  • ​This is due to the large contact area between the silicone material

  and anterior capsule

• ​This stimulates cell proliferation and fibrosis 

 

• The posterior capsule remains clear for several years

  • ​This is due to the low adhesion to extracellular components which cause this form of opacification (PCO)

 

 

• Less commonly used material 

  • Not suitable for Microincision Cataract Surgery (MICS)

  • This is due to the larger corneal incision silicone IOLs require

 

• More recently, a silicone IOL was created, in which UV exposure is used to change the power post-implantation. 

 

•  Silicone oil is used as a tamponading agent

  • This agent, without leaking through retinal tears, 

  acts as a 'plug' in retinal detachment surgery

 

•  However, silicone droplets are known to stick to the

      the posterior IOL surface

•  YAG capsulotomy is used to remove the oil, causing

      silicone droplets to deposit onto the posterior IOL

      surface

 

•  This means the IOL needs to be replaced

 

 

 

ACRYLIC

HYDROPHOBIC FOLDABLE ACRYLIC

 

• Have the ability to be folded, pushed and pulled 

  • No permanent structure changes occur

 

• Copolymers of acrylate and methacrylate are derived from PMMA 

  • Therefore make the material flexible and durable

 

• Lens optic diameter: 5.5 -7.0mm 

 

• Overall length: 12 - 13mm

 

• High refractive index

  • ​ Therefore, thin and foldable

    • Able to pass through a small incision (2.2mm) 

  • Associated with photopsia because of the high index

         and low anterior curvatures 

 

• Wettability angle: smaller than silicone, measuring at 73º

 

• Low water content 

 

 

• Soft copolymers

  • Prone to scratches and permanent fingerprints

  • Known to decentre, therefore surgeons must be extra cautious during implantation

 

• There has been less PCO found, and withstanding considerable damage from YAG capsulotomy 

  • Acrylic IOLs do not attract silicone droplet deposits from silicone oil

 

• 'Glistenings' have been reported

  • Newer materials have been introduced to prevent further uptake of water

 

 

HYDROPHILIC FOLDABLE ACRYLIC 

• Most common material for IOLs

• Consists of a mixture of hydroxyethylmethacrylate (poly-HEMA) and hydrophilic acrylic monomer

 

 

 

 

 

 

 

 

 

 

 

 

• Refractive index: 1.43

 

• Most lenses have a water content ranging between 18 and 26%

 

• Wettability angle of 50º

  • Because of their hydrophilic surface, the IOLs are soft and

         have good biocompatibility

• The flexible surface means that there is minimal damage to the folding and insertion of lens 

 

• For implantation of the IOL, the corneal incision required only needs to measure 2mm or less

  • Therefore, an appropriate choice for MICS

 

 

• These lenses are advantageous to surgeons as they are easier to handle

  • ​Also have been known to rarely dislocate if implanted accurately

 

 

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• Following surgery, PCO occurs at a higher rate that other materials such as silicone and hydrophobic acrylics

  • If YAG capsulotomy is carried out, the lens is more susceptible for laser damage

 

 

 

 

 

 

 

 

 

 

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• The incidence of photopsia is low in comparison to lenses of a hydrophobic nature

  • But there is a concern of optic opacification due to calcium deposits

    • This concern has been associated with, but may not be due to, certain IOL types

 

 

 

 

 

COLLAMER

 

• Combination of 'collagen' and 'polymer'

• Produced by STAAR surgical 

• Water content: 40%

  • Collamer is soft and IOLs are able to unfold slowly

    • Therefore, implantation is easier 

 

 

• Collamer combines the best components of silicone and acrylic lenses

  • Higher refractive index than silicone (1.442), so can be folded into an even smaller arrangement

    • The procedure can be carried out through a smaller corneal incision 

  • It is a negatively charged and hydrophilic material, thus is required to stay wet during surgery

  • Due to the low elastic memory of Collamer, it is 'pushed out' of the injection cartridge, giving more control to the surgeon

 

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• Post-surgical inflammation of the eye is absent with this material 

  •  Collamer attracts a protein known as fibronectin, forming                                                                a layer around the IOL, enabling the lens to be 'shielded' from                                                  attack from the body's immune system