Surgically implanted lenses, or phakic IOLs, are increasingly being seen as an alternative for people seeking more permanent correction of common vision problems. While there are clear benefits – they cannot be felt in the eye, require no maintenance and can achieve superb quality of vision – careful patient selection is crucial.
While LASIK remains the most commonly performed refractive surgical procedure, there are many patients for whom LASIK is not appropriate. Patients with high myopia, high hypermetropia and thin corneas cannot be safely or predictably treated with LASIK.
For low to moderate myopes and low hyperopes with a thin cornea, I prefer a surfaced based corneal procedure (ALSA, PRK) (Figure 1). However, there is a definite zone in high myopia for which phakic IOLs are my preferred option.
While this makes up only a small percentage of the total number of patients in my practice (Figure 2), these lenses are becoming increasingly more sophisticated and our experience, length of follow-up and confidence in these devices, is growing.
these lenses are becoming increasingly more sophisticated and our experience, length of follow-up and confidence in these devices, is growing.
Options Available
Phakic IOLs differ from standard intraocular lenses (IOLs) in that they are placed inside the eye without removal of the crystalline lens. They can correct both myopia and hypermetropia, however the platform for myopia is more widely used and better developed.
There are basically three types of phakic IOLs, which are categorised by their final position within the eye.
1. Prelenticular: The most widely used is the Staar Visian ICL (intraocular contact lens).
2. Iris Clip: Both the Artisan and Verisyse have the same platform, but are marketed by different companies.
3. Anterior Chamber: The Alcon Cache is the latest and best example of this style of lens.
Each of these lenses has its proponents and clear advantages and disadvantages. The Staar ICL (Figure 3) is probably the easiest for the surgeon to insert and, for any cataract surgeon, the learning curve is relatively short. The main problem with this lens is the incidence of cataract formation over time. Clinically significant cataracts formed in more than five per cent of cases in a 2007 US Food and Drug Administration (FDA) trial. This may necessitate cataract removal in some cases, which would precipitate an increased risk of retinal detachment in these myopes.
The Iris Clip lens (Figure 4) has been my preferred lens for many years. It is more cumbersome to insert but has the capacity for hyperopic and astigmatic correction. The foldable platform has meant the incision size is now comparable to the other styles. Dislocation can occur and the learning curve is relatively steep. Rare cases of un-cosmetic pupillary distortion have been reported, but I have not encountered this problem. Cataract formation is rare with this lens.
The new Alcon Cache (Figure 5) is placed in the anterior chamber and, unlike the other two varieties, does not require a peripheral iridectomy. It is easy to insert and as long as the anterior segment parameters are adhered to, is a safe and reasonable option for myopes. There is no toric or hypermetropic solution with this platform.
Risks Exist
Phakic IOLs are safe – but not perfectly safe. Entering the eye in any operation runs the risk, however rare, of endophthalmitis. The main concern with phakic IOLs, which has prevented them taking over from LASIK for moderate degrees of myopia, is their long-term impact on endothelial cell count. There is still some concern that these lenses may be causing an accelerated endothelial cell loss over a 10 year period.
It is for this reason, and this reason alone, that I am cautious in offering these lenses to my patients. There are, however, patients with high myopia for whom these lenses are appropriate because they are contact lens intolerant or can’t wear glasses or contacts in their chosen occupation. In these situations, the risk/benefit analysis makes sense. The quality of vision these patients achieve is often superb. The elimination of their high myopia removes a minification effect and their uncorrected visual acuity is often better than their best corrected vision prior to the surgery.
If, as the trends are suggesting, endothelial cell loss is flattening out with time, these lenses will become used more widely and with more confidence. There is no doubt that when appropriately used, they can make a significant difference to people’s lives but, at this stage, careful patient selection is necessary.
Dr. Gerard Sutton is the inaugural Sydney Medical School Foundation Professor of Corneal and Refractive Surgery at Sydney University.
