Intra ocular lenses for cataracts
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Intraocular lenses (IOLs) are designed to primarily restore the refractive power of the eye after a cataract surgery. However, with rapid technological breakthroughs, IOLs are now available in various new and sophisticated designs. These advanced models offer specialized functions like multifocality, toric corrections, pseudoaccommodation, blue-light blocking, photochromic operations and what not. Most of these new designs have been triggered by advancement in surgical methods such as very small incisions and wavefront aberrometry. A look at these various IOLs according to their specific features reveals an array of choices.

Multifocal intraocular lenses

There are a few important points to remember before opting for a multifocal IOL:

  • Control of astigmatism is essential.
  • Accurate biometry is needed.
  • Patients must be selected carefully to reduce the high probability of decreased contrast sensitivity and glare caused by these lenses.
  • Surgical method has a direct effect on the outcome on the use of these lenses.

The various multifocal lenses currently available are:

Array

The Array is the first multifocal IOL approved by the Food and Drug Administration (FDA). It is a three-part multifocal IOL made of a silicone material with a refractive index of 1.46. Some studies that compared bilateral implantation of the Array with a monofocal lens (at the backdrop of visual quality and patient feedback) reported the following points:

  • Better uncorrected and distance corrected near visual clarity.
  • Better overall eyesight.
  • Lesser imperfections of visual operations.
  • Reduced spectacle dependency.

However, some other studies failed to report noteworthy changes in contrast sensitivity with average and high glare.

ReZoom

This second-generation refractive, multifocal IOL is an adaptation of the Array. It is a recent product from Advanced Medical Optics, California. This lens is created from a hydrophobic acrylic material with a refractive index of 1.47.

The features of this lens are:

  • Optical design based on the Balanced View Optics Technology, with five concentric zones modified from the Array model.
  • Integrates the new OptiEdge design combining three components:
    1. A rounded anterior edge to decrease glare.
    2. A sloping side edge to reduce the surface area that can trigger internal reflections and to disperse internal reflections away from the retina.
    3. A square vertical posterior rim to help prevent PCO.

ReSTOR

The ReSTOR lens is also a current addition to the multifocal IOL family. This is an apodized, diffractive IOL, adapted from a single-piece AcrySof lens. Its design ensures suitable near and far vision when the pupil is small, for instance while reading. On the other hand, it adjusts to a large pupil condition for instance at nighttime and ensures suitable distance vision while minimizing unexpected visual aberrations.

Tecnis

This lens features the Z-Sharp Optic Technology. It has an anterior aspheric surface that offsets positive corneal aberration. A Tecnis design (model ZM001) with a diffractive posterior surface is currently being developed.

Toric intraocular lenses

TORIC IOLS are designed to correct cataract related pre-existing astigmatism. Hence, they must ensure proper centration, fixation and constancy without rotational movements.

The Staar Surgical

This silicone-made posterior chamber IOL is a single-piece toric (models AA-4203TF and AA-4203TL). It provides cylindrical correction with a spherical optic.

Alcon’s model SA60TT

This recently launched lens is another toric model adapted from a single-piece AcrySof IOL. This lens shows more stability and less postoperative rotation.

Blue Blocking Intraocular Lenses

Some IOLs are specially designed to absorb light that can harm the eye. The human eye becomes more vulnerable to blue light when the natural crystalline lens of the eye yellows with age. The blue light blocking IOLs replicates the transmission ability of the aging crystalline lens and shields the retinal pigment epithelial cells from blue-light hazards. This also reduces the risk for a condition called macular degeneration.

The AcrySof Natural (SN60AT)

This is one such blue blocker adapted to a single-piece AcrySof and provides higher protection than just UV rays. Disadvantages of these yellow IOLs are a probable effect on color and night vision (since blue light is required more for night than for day vision).

SmartYellow IOL

The problem of night vision is being addressed by the SmartYellow IOL. This is a three-piece lens created from a proprietary hydrophobic acrylic substance and more importantly has photochromic properties that can address the problem of night vision with yellow lenses. Studies have suggested that its photochromic changes are reversible, can be replicated and is ensures long-term stability.

Accommodative Intraocular Lenses

IOLs are also designed to restore the accommodation ability of the eye. The Eyeonics CrystaLens (model AT45) is created from a third-generation silicone material (Biosil) with a refractive index of 1.43. It was approved by the FDA in 2003 with the benefit of estimated addition of 1 D of accommodation compared to monofocal lenses.

The Synchrony IOL is a one-piece silicone lens that is based on the conventional Helmholtz’s theory of accommodation. It is now under clinical examination. Bausch and Lomb is also currently developing another single-piece molded silicone dual-optical accommodating IOL.

Aspheric Intraocular Lenses

Aspheric IOLs correct spherical aberrations of the human eye. Z-Sharp Optic Technology has been implemented on the CeeOn Edge IOL, model 911 platform to manufacture Aspheric IOLS. Currently available IOLs like Tecnis also have positive spherical aberration.

The AcrySof aspheric (model SN60WF), adapted from the single-piece AcrySof, has negative spherical aberration. Both the Tecnis and the SN60WF lens offset the average spherical aberration in cataract cases.

The SofPort Advanced Optics (AO) (model LI61AO) from Bausch and Lomb does not add negative spheric aberration to the eye, but it is Aberration-free when compared to the other aspheric IOLs.

Intraocular Lenses For Very Small Incisions

The invention of microincision surgical techniques that enabled cataract removal through clear corneal incisions as small as 1 mm, led to the manufacture of suitable IOLs. One such latest model that can be inserted through a sub 2-mm incision (1.45-mm) is the UltraChoice 1.0.

Another new concept of very-small-incision IOLs called SmartIOL, which can also restore accommodation.

Light Adjustable Lens

Calhoun Vision is developing a three-piece silicone lens with photosensitive silicone subunits. This ensures a non-invasive implantation and definitive refraction to the patient. It also provides correction of higher-order eye deviations like the tetrafoil patter and aspheric conditions, besides hyperopic, myopic, and astigmatic therapy.

Implantable Miniature Telescope

The implantable miniature telescope is an exclusive visual prosthetic gadget that addresses advanced stage age-related macular degeneration. It is developed by VisionCare Ophthalmic Technologies and has the additional feature of ensuring a natural cosmetic look. Another model of the telescope is being adapted for pseudophakic cases.

 
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