INTRAOCULAR LENS IMPLANTATION

Presently, intraocular lens (IOL) implantation is the
method of choice for correcting aphakia. Its
advantages and disadvantages over spectacles and
contact lenses are described in aphakia (see page
31).
The IOL implant history had its beginning on
November 29, 1949, when Harold Ridley, a British
ophthalmologist, performed his first case. Since then
history of IOLs has always been exciting, often
frustrating and finally rewarding and now highly
developed.
Types of intraocular lenses
During the last two decades a large number of
different types and styles of lenses have been
developed. The commonly used material for their
manufacture is polymethylmethacrylate (PMMA).
The major classes of IOLs based on the method of
fixation in the eye are as follows:
1. Anterior chamber IOL. These lenses lie entirely
in front of the iris and are supported in the angle
of anterior chamber (Fig. 8.23). ACIOL can be
inserted after ICCE or ECCE. These are not very
popular due to comparatively higher incidence of
bullous keratopathy. When indicated, ‘Kelman
multiflex’ (Fig. 8.24A) type of ACIOL is used
commonly.

2. Iris-supported lenses. These lenses are fixed on
the iris with the help of sutures, loops or claws.
These lenses are also not very popular due to a
high incidence of postoperative complications.
Example of iris supported lens is Singh and Worst’s
iris claw lens (Figs. 8.24B and 8.25).
3. Posterior chamber lenses. PCIOLs rest entirely
behind the iris (Fig. 8.26). They may be supported by
the ciliary sulcus or the capsular bag. Recent trend is
towards ‘in-the-bag-fixation’. Commonly used model
of PCIOLs is modified C-loop (Fig. 8.24C).
Depending on the material of manufacturing, three
types of PC-IOLs are available :
i. Rigid IOLs. The modern one piece rigid IOLs are
made entirely from PMMA.
ii. Foldable IOLs, to be implanted through a small
incision (3.2 mm) after phacoemulsification are
made of silicone, acrylic, hydrogel and collamer.
iii. Rollable IOLs are ultra thin IOLs. These are
implanted through micro incision (1mm) after
phakonit technique. These are made of hydrogel.
Indications of IOL implantation
Recent trend is to implant an IOL in each and every
case being operated for cataract; unless it is
contraindicated. However, operation for unilateral
cataract should always be followed by an IOL
implantation.

Calculation of IOL power (Biometry)
The most common method of determining IOL power
uses a regression formula called ‘SRK (Sanders,
Retzlaff and Kraff) formula’. The formula is P = A –
2.5L – 0.9K, where:
P is the power of IOL,
A is a constant which is specific for each lens
type.
L is the axial length of the eyeball in mm, which
is determined by A-scan ultrasonography.
K is average corneal curvature, which is
determined by keratometry.
The ultrasound machine equipped with A-scan
and IOL power calculation software is called
‘Biometer’.

Primary versus secondary IOL implantation
Primary IOL implantation refers to the use of IOL
during surgery for cataract, while secondary IOL is
implanted to correct aphakia in a previously operated
eye.
Surgical technique of anterior chamber IOL
implantation
Anterior chamber IOL implantation can be carried out
after ICCE and ECCE. After completion of lens
extraction, the pupil is constricted by injecting miotics
(1 percent acetylcholine or pilocarpine without
preservatives) into the anterior chamber. Anterior
chamber is filled with 2 percent methylcellulose or 1
percent sodium hyaluronate (Healon). The IOL, held
by a forceps, is gently slid into the anterior chamber.
Inferior haptic is pushed in the inferior angle at 6
O'clock position and upper haptic is pushed to
engage in the upper angle (Figs. 8.17 G & H).
Technique of posterior chamber IOL implantation
Implantation of rigid intraocular lens. PCIOL is
implanted after ECCE. After completion of ECCE, the
capsular bag and anterior chamber are filled with 2
percent methylcellulose or 1 percent sodium
hyaluronate. The PCIOL (Fig. 8.24C), is grasped by
the optic with the help of IOL holding forceps. The
inferior haptic and optic of IOL is gently inserted into
the capsular bag behind the iris at 6 O'clock position
(Fig. 8.18F). The superior haptic is grasped by its tip,
and is gently pushed down and then released to slide
in the upper part of the capsular bag behind the iris
(Fig. 8.18G). The IOL is then dialled into the horizontal
position (Fig. 8.18H).
Implantation of foldable IOLs is made either with the
help of holder-folder forceps or the foldable IOLs
injector.