Intraocular Lens (IOL)
Which Intraocular Lens (IOL) is most suitable for my
from cataract and planning for cataract surgery are
faced with this difficult question & a frustrating
list of choices. I will attempt to make it simple,
let me start by explaining a few characteristics of
the Intraocular Lenses (IOL):
What is Intraocular
In cataract surgery
the natural lens of the eye is removed. This leads a
significant decrease in the optical convergence
power of the eye or hypermetropia. Intraocular
lenses are small lenses made of polymers and
implanted into the eye in place of natural lens to
help focus the light on to retina.
In conventional cataract surgery & in SICS a large
cut / incision is made in the eye to remove the
cataract. This is followed by insertion of a rigid
6.0/6.5 mm lens through the incision into the eye.
These lenses are rarely used these days.
In phacoemulsification the entire operation done
through a small hole of 3.0 mm or less. It is not
possible to implant a rigid lens. This difficulty is
overcome by use of very flexible lenses which can be
folded and loaded in special injectors aninserted
through the small hole into the eye. These are
currently the preferred lens to be used.
(Silicone, Hydrophillic & Hydrophobic Acrylic)
Lenses are commonly made of silicone or acrylic
polymer (hydrophobic or hydrophillic).
Silicone was used in older lenses & gave good
optical results in the immediate post-operative
period. But these lenses were somewhat bulky and
lead to severe thickening of anterior & posterior
capsules (membrane covering of natural lens which is
left behind to provide support for artificial
intraocular lens). This lead to deterioration of
vision and required treatment by YAG Laser
Hydrophillic Acrylic lenses are highly flexible and
slim, therefore, can be introduced through extremely
small incisions. They have good immediate visual
results but suffer from tendency to cause thickening
of posterior lens capsule.
Hydrophobic Acrylic lenses are slightly less
flexible and somewhat thicker than their
hydrophillic counterparts. But they are extremely
inert and do not lead to lens capsule thickening.
Due to these properties they are ideal for use in
children, young adults and the eyes predisposed to
inflammation. Being hydrophobic in nature it is
possible to incorporate a color tint to avoid blue
chromatopsia after surgery.
Spheric are the conventional lenses where both
surfaces of the lens are uniformly curved or are
part of a sphere. These lenses have inherent problem
of spherical aberrations caused by excessive bending
of light at the edges.
Aspheric or advanced optics lenses have their
curvatures flattening out towards the periphery or
edge, thereby, minimizing spehrical aberrations.
Aspheric lenses give much sharper vision and better
contrast but due to decreases depth of focus, the
need for reading glasses becomes more urgent. On the
other hand spheric lenses, though lack the sharpness
& contrast to some extent but have better depth of
focus leading to slightly better near vision.
However, almost all lens manufacturers are replacing
their spherical lenses with aspheric.
have a single focal length and unlike the natural
lens do not possess the ability to change the focus.
Therefore the patient needs to wear reading glasses
in order to focus at near fine print. But these
lenses provide much better contrast and image
Multifocal lenses have 2 foci - a distance and a
near focus. This is achieved by having multiple
optical zones fashioned in the lens in the form of
alternating rings for distance and near. This leads
to splitting of light into distance and near foci.
As a result both the distant and near objects can be
focussed in the eye at the same time. However, the
contrast and sharpness of the vision is reduced
significantly. There lenses are also prone to more
glare and haloes of light during driving at night
So for patients who need sharp vision and better
contrast and do not hesitate in wearing reading
glasses, monofocal lenses are most suitable.
Whereas, those who do not want dependence on reading
glasses but are willing to compormise on contrast
and sharpness of vision, can opt for multifocal
Please note that both eyes should have the same type
of lens - monofocal OR multifocal.
Toric vs. Non-toric
Toric lenses, besides having spherical power, also
have cylindrical power which corrects astigmatism
present in the eye. Non-toric lenses do not have any
cylindrical power. Eyes with no or negligible
astigmatism require non-toric lens and the eyes with
significant astigmatism would benefit from toric
lenses. Toric lenses are especially useful in
patients with high degree of against the rule
corneal astigmatism which is not amenable to
correction but incision placement.
Currently I prefer to use Foldable
Hydrophobic Acrylic Aspheric Monofocal Lens
with a natural color tint and toric where
required. Multifocal is preferred where
cosmetic requirements is more important and
there are no critical visual needs.
Senior Eye Surgeon
New Delhi & Gurgaon, India
Updated on 3 September 2009