The natural lens of the eye helps to focus light on the retina for clear vision. However, our clear natural lens begins to become cloudy over a period of time and this is known as cataract formation. It is a degenerative condition that interferes with vision. This impairment of vision affects the quality of life. Generally, cataract formation is age-related, but very rarely this condition can occur at birth or in younger people as well. If left untreated,  cataract can lead to blindness.

More about Intraocular Lens Implants (IOLs)

The only treatment for this degenerative condition is surgical removal of the cataract. The natural lens is replaced with an artificial lens/ Intraocular Lens Implant (IOL). In the majority of cases, treatment of cataract is effective, and after the surgery, most patients have excellent vision.

Cataract surgery procedure
Figure1. Cataract surgery procedure (phacoemulsification)

Before the surgery, your ophthalmologist or eye surgeon will recommend or ask you to choose an intraocular lens implant or artificial lens to be placed in your eye. An IOL or intraocular lens is a clear medical device designed to replace the natural lens of the eye. Cataract surgery involves removal of the natural lens and implantation of an artificial lens to offer improved colour contrast and clear vision.

Today, these intraocular lens implants are easily available in various materials and designs. With certain artificial intraocular lenses, amazing spectacle-free results are achieved even for presbyopia (age-related farsightedness) and astigmatism. The cataract surgery and artificial lens improve visual accuracy and precision for the majority of the patients.

Types of Intraocular Lenses according to design
Depending on your life-style and visual needs, your eye surgeon will recommend the best intraocular lens for you. Here are some commonly used types of intraocular lenses:

Monofocal IOLs: They are the simplest type of intraocular lenses available in the market.  Monofocal intraocular lenses have a single zone of clear focus and hence offer excellent distance vision. However, you have to depend on reading glasses for near work. If you wish to have excellent distance vision but do not mind using near vision glasses after the surgery, opt for these lenses.

Monofocal IOLs
Figure 2. Monofocal IOLs

Multifocal IOLs: These types of lenses offer good vision for distance as well as near and greatly reduce dependence on spectacles. In Multifocal intraocular lenses, one lens incorporates both near and distance powered segments. The base power segment of the lens bends light from distant objects to a single focal point on the retina. The higher power segments bend light coming from near objects to the same focal point on the retina.

You must also consider certain drawbacks of using multifocal IOLs including the glares when driving at night. Some people may need glasses to read very fine print even after the surgery. Also, intermediate distance vision may not be perfect with these lenses. Thus, Multifocal IOLs are excellent for those who do not like to wear eyeglasses and don’t drive much at night. However, the overall quality of vision is satisfactory.

Multifocal IOLs
Figure 3. Multifocal IOLs

Toric IOL:Unlike other intraocular lenses, Toric IOLs correct pre-existing corneal astigmatism or cylindrical power. These lenses minimise the residual refractive cylinder and thus, improve the quality of uncorrected distance vision. If you have a cylindrical number in the glasses and wish to get rid of the spectacles for distance, opt for the Toric IOLs. Multifocal IOLs also come with a toric design for correcting cylindrical power and providing excellent spectacle free vision. However, the cost of these sophisticated lenses are on the higher side.

Vision with various types of IOLs
Figure 4. Vision with various types of IOLs

Accommodative IOLs: Accommodative intraocular lenses offer good vision for all distances without eyeglasses. They are designed like the natural lens of the eye and are supposed to move in the eye to simulate the natural lens. Though preliminary results are encouraging, more studies are required to know the effectiveness of these lenses in correcting vision compared to monofocal IOLs.

Types of Intraocular Lenses according to structure:
These incorporate the latest technology used to improve the quality of vision:

Aspheric design: These lenses improve the quality of vision and contrast sensitivity at night by reducing or removing the optical aberrations. Today, most of the higher end monofocal, multifocal and toric lenses have aspheric design and it is definitely recommended to choose this design for better quality of vision.

aspheric monofocal vision
Figure 5. Monofocal versus aspheric monofocal vision

Blue light filtering IOLs: Ideally, the natural lens of the eye cuts out blue light which is harmful to the very sensitive macula or central part of the retina. Blue light filtering IOLs are impregnated with yellowish pigment, which blocks blue light. So, people with macular degeneration problem can opt for the blue light filtering IOLs. Blue-light filtering IOLs are available in monofocal, multifocal and toric designs.

Intraocular Lens Materials: Non-foldable Polymethyl methacrylate (PMMA) was initially used as an intraocular lens material. However, with the advancement of technology and science, today, a plethora of intraocular lens materials are used safely. The intraocular lens materials currently in use are foldable materials and include hydrophilic acrylic, hydrophobic acrylic, UV-light filtering, and hydrophobic silicone.

Hydrophilic Acrylic (or hydrogel): This material is heterogeneous and also has high water content. Because of the hydrophilic material, the chances of posterior capsular opacification (a late complication of cataract surgery where the posterior capsule of the lens/ support structure of the lens gets opacified, thus causing deterioration of vision) are higher. This can however, be treated easily with Nd:YAG capsulotomy done in the OPD.

Hydrophobic Acrylic: It is an ideal intraocular lens material because it has a high refractive index, very low water content, and a high memory. Because of the hydrophobic material, this lens is not as much predisposed to cause posterior capsular opacification.

Light Filtering: Most intraocular lens materials contain ultraviolet (UV) light-blocking chromophores. These elements help to filter out the UV light.

Types of Intraocular Lenses according to site of placement: Normally, the artificial lenses are placed in the capsular bag of the natural lens using the natural lens support structure. However, in some cases where the capsular or zonular support is absent/ lost/ insufficient, this is not possible. In such instances, the intraocular lens is fixed to other sites in the eye with the help of advanced special techniques.

Scleral Fixated IOLs (SFIOL): Scleral Fixated Intraocular lens is a brilliant option in people with insufficient capsular support or zonular support. Here the lens is anchored to the sclera (white part of the eye) with or without the use of sutures.

Anterior Chamber IOL: Here the lens is placed in the front portion of the eye.

Iris Fixated IOL: Here the lens is anchored to the iris (coloured portion of the eye) of the eye.

Myths about Intraocular Lens

Myth 1: One of the most common myths about the intraocular lens is that you may not need spectacles after surgery. However, depending on the lens you choose, you may need to use your glasses for reading.

Myth 2: Implantation of the intraocular lens is very risky. Yes, any type of surgery involves risk but the fact is cataract surgery with intraocular lens implantation is the most successfully performed surgery in the word.

Myth 3: Intraocular lens have a shelf life and they may not last. The fact is, once placed intraocular lenses last a lifetime.

Myth 4: I can choose an IOL for the time being, later I can replace it with a better lens. The fact is once implanted it is very risky to try and replace an IOL. So choose your lens wisely!

A wide range of eye lenses is available in the market. Talk to your eye surgeon and choose your lens wisely and make an informed decision to improve the quality of your vision and quality of your life.