Secondary intraocular lens implantation and exchange

In lens surgery, we may come across two uncommon situations: either we have to fit a secondary intraocular lens (IOL) or exchange the IOL the patient is wearing which was fitted in a previous surgical procedure. 

Secondary implants are fitted on patients that do not wear an IOL or patients that already wear and IOL and we give them a second lens to correct a graduation error, a refractive error. 

Secondary implants in patients who do not have a crystalline lens are performed in cases where there was an accident that led to the removal of the crystalline lens, a traumatic cataract or else during surgery the surgeon decided not to fit a lens.

Or in cases where the crystalline lens has dislocated from the vitreous chamber, the patient may be operated on by a vitrea and retina surgeon who removes the crystalline lens and the anterior chamber surgeon implants the secondary IOL.

Lens exchanges mean removing a lens that had been fitted on a patient and fitting another. There are multiple causes. 

Generally, lens exchanges are performed when there is an error in the lens calculation or what we call a refractive surprise: the lens has been calculated, implanted and the patient is unhappy with the graduation, something which cannot be corrected by any other means.

Normally, it occurs with large errors, more than 2, 3 or 4 dioptres. Another reason for a lens exchange is that the lens implanted has become opaque over time. This situation is rare and very uncommon, but we have seen over the years that a particular lens model can opacify in some cases.

Secondary implants can be implanted in the anterior or posterior chamber, that is to say, in front or behind the iris, the colour of the eyes. We can fit posterior chamber implants by suturing them to the sclera wall. We implant a lens and we fix it to the sclera wall with two sutures.

These lenses remain there for a long time, generally for the patient's whole life, although over time in special cases the sutures may break and the implants may have to be fixed in place once again in a separate operation. 

An iris-fixated lens may also be fitted. These lenses have two little legs like a crab that are fixed with a pinch to the iris tissue. They can be fitted in front or behind the iris.

We prefer to fit them behind the iris, as they are separate from the cornea and therefore they do not harm the corneal endothelium, although on some occasions, for ease of viewing and to prevent them from falling into the vitreous cavity, we fit them in front of the iris. 

A lens exchange involves removing a lense from its place, generally the capsular bag.

It is not an easy procedure; much precaution and meticulousness is needed to stop the capsular bag from breaking and leaving us without supports for the new lens. If we can remove the lens from the capsular bag properly, we can use it as a support to implant a second lens with the desired graduation.