GLUED IOL

Performing a glued intraocular lens (IOL) is a challenge in patients who have either larger or smaller than normal eyes. The challenge in large eyes is to get a sufficient degree of haptic exteriorised, resulting in insufficient haptic tuck and a potentially unstable IOL.

The challenge in small eyes on the other hand is an unnecessary extent of haptic that is exteriorised. Large optics relative to the eye may also become significant in patients who have severe micro cornea.

LARGER THAN NORMAL EYES

As it is the haptic tuck that is responsible for the stability of the glued IOL, obtaining a sufficient length of haptic to tuck is crucial. When planning for a glued IOL, it is important to first measure the horizontal white to white diameter of the cornea and if more than 11.5mm, it may be preferable to opt for a vertically oriented glued IOL.

For this, the surgeon shifts to the temporal side of the patient and the two scleral flaps are created diametrically opposite each other in the vertical axes. Ideally, broad flaps should not be created as this results in a significant length of haptic traversing under the flap and less available haptic at the flap edge to be tucked.

Ideal flaps should not be more than 2 to 2.5mm in width along the limbus (Figure A). This allows a greater length of haptic that can be tucked intrasclerally and thereby increases the stability of the IOL. In case broad flaps have been created, the sclerotomies are skewed to the opposite edges of the flap in such a manner that they still stay 180 degrees opposite each other. (Figure B)

As this brings the sclerotomy closer to one end of the flap, the degree of haptic tuck proportionally increases. If the sclerotomies have already been placed centrally under broad flaps, the intra-scleral tunnel may be initiated through the bed of the scleral flap. (Figure C)

Another option that can be utilised for increasing the degree of haptic tuck is creating the sclerotomy closer to the limbus. A sclerotomy placed about 1 to 1.5mm posterior to the limbus is ideal. Going more posterior to this displaces the plane of the entire IOL backwards towards the posterior pole of the globe, and thereby decreases the length of haptic available for tucking. (Figure D)

With anteriorly displaced sclerotomies, the advancing edge of the needle used to create the sclerotomy passes close to the iris base and unless performed carefully can result in an iridodialysis.

Certain precautions may be utilised to avoid this. A blunt needle should not be used. In case the surgeon is operating with an anterior chamber maintainer (ACM) in place, the flow of fluid from the ACM pushes the iris backwards bringing the advancing edge of the needle close to the iris base.

To avoid this, the ACM should be turned off while creating the sclerotomy. On the other hand, with an infusion cannula fixed through the pars plana, the direction of fluid flow tends to bellow the iris forwards and therefore it is easier to create a sclerotomy without causing damage to the iris base. In this case the infusion may be left on while creating the sclerotomy.

The direction in which the needle is introduced into the eye is also important - the tip of the needle should be facing perpendicularly down towards the floor rather than towards the centre of the eye in order to avoid the iris root. Once the resistance of the eye wall has been crossed, the needle is again pointed towards the centre of the eye till the tip is visualised.

Both sclerotomies should be kept at the same distance from the limbus in order to avoid an IOL tilt. A too posteriorly placed sclerotomy resulting in an inadequate length of haptic exteriorised may be corrected by creating a new sclerotomy anterior to the old one, taking care to utilise all the precautions mentioned to avoid damaging the iris base.

Using the hand shake technique the externalised haptic is then re-internalised into the eye and then again re-externalised through the freshly created anteriorly placed sclerotomy.

Two end gripping micro forceps are utilised in a bimanual manner. One of the forceps is introduced through the limbal paracentesis. The haptic is then internalised through the sclerotomy into the jaws of the first forceps. The second forceps is then introduced through the anterior sclerotomy and the haptic is transferred from hand to hand in a bimanual manner till it is held at the tip and is externalised out through the anterior sclerotomy.

On entering the eye through the anterior sclerotomy, the ACM should be momentarily put off. This anteriorisation of the haptic also brings the plane of the IOL optic anteriorly and therefore the final position of the sclerotomy should be symmetrical on both sides to avoid an IOL tilt.

Care should also be taken to not take it anterior enough to cause optic capture. Another option available for larger eyes is to use an IOL that has a larger overall diameter. The Staar AQ2010V IOL has a larger overall IOL diameter of 13.5mm and thereby increases available haptic to be tucked. Customised IOLs may also be ordered.

In eyes smaller than normal, especially with microcornea, other associated abnormalities may co-exist and might end up requiring placement of an IOL in the presence of defective capsule.

The problem here is exactly opposite - the length of haptic externalised is excessive.

Long intra-scleral tunnels are then required, which are difficult and dangerous to create. This situation may easily be managed by trimming the haptic to the desired length with a Vannas scissor and then tucking the rest of the haptic in. An IOL with smaller diameter optic may also be preferable to avoid crowding of the anterior chamber.

Thus we see, though challenging to perform the glued IOL in smaller and larger than normal eyes, it can be successfully performed provided required precautions are taken.

* Dr Soosan Jacob is a Senior Consultant Ophthalmologist at Dr Agarwal’s Eye Hospital, Chennai, India and can be reached at dr_soosanj@hotmail.com