Intraocular Lens (IOL)

Intraocular Lens (IOL) implanted after surgery are of different types. Broadly speaking there are five features available in lens design; Lens material, Ultraviolet Filter, Square Edge Design, Aspheric Design, and Focality. Based on these features IOLs can be of different types.

1. Material: Various lens materials such as polymethylmethacrylate (PMMA), Silicone, hydrophobic & hydrophilic acrylic materials are available. PMMA are hard non-foldable lenses which are used in large incision (6 – 10 mm) cataract surgery (MSICS & ECCE). Out of foldable lenses, Hydrophobic acrylic is considered best because of its best long-term effects in preventing posterior capsular opacification (PCO). Foldable lenses are generally implanted after micro incision (2.2 mm) phacoemulsification surgery. PCO present 6 months to 1 year after surgery and is characterised by decrease in vision, which require Nd: YAG Laser Capsulotomy for restoring lost vision. Complications of Nd: YAG Laser Capsulotomy are rare but serious, this include 2% chances of retinal detachment and floaters which are very common. 

2. Ultra Violet (UV) filter: Since the human lens absorbs UV radiation, individuals who have had cataract surgery are at increased risk of retinal injury from sunlight unless a UV absorbing intraocular lens was inserted at the time of surgery. Individuals with retinal dystrophies or other chronic retinal diseases (diabetes, hypertension etc) may be at greater risk since their retinas may be less resilient to normal exposure levels.

3. Square Edge design: IOLs with a square posterior optic edge have been associated with better results in terms of posterior capsule opacification (PCO) prevention, regardless of the material used in their manufacture.

4. Aspheric Design: Higher order aberrations are corrected using aspheric design, which gives greater contrast sensitivity, particularly in dim light, and better vision during night-driving.

5. Focality: 

a. Monofocal lenses correct for distance vision, allowing the person who receives it to do things such as driving and going to the movies without needing glasses. The monofocal lens is the most basic lens available. With a monofocal lens, you will still need glasses for intermediate and near distances, such as when you are working on a computer or reading a book.

b. Multifocal lenses correct for all distances and give you good near and far vision but you may still need glasses for reading very fine print. One possible drawback to these lenses is you may experience halos around lights when driving at night. However, this usually fades over time.

c. Extended Depth of Focus (EDOF) is a new technology, in contrast to multifocal intraocular lenses used in treatment of presbyopia, EDOF lenses work by creating a single elongated focal point to enhance “range of vision” or “depth of focus that provides high-quality vision over a continuous range. With EDOF lenses chances for using glasses is almost nil and driving at night is also comfortable. The reading of fine print usually requires glasses. 

d. Trifocal lenses are the most advanced intraocular lenses available today, providing clear vision for close, intermediate and far distances, without gaps in between. They are designed to enable a high degree of independence from glasses for patients leading an active life and wishing to do without prescription glasses. 

e. Toric lenses correct for astigmatism, which is caused when the cornea is shaped irregularly. Toric lenses can be Monofocal, Multifocal, EDOF or Trifocal.