When dealing with post PK astigmatism the literature is heavily populated with several surgical techniques which can be broadly classified in to secondary surgical procedures performed on the corneal graft and intraocular procedures which involves implanting an IOL either in the anterior or posterior chambers. Of the secondary procedures performed on the corneal graft laser procedures like LASIK seem to be more predicable in correcting the post PK refractive error when compared to AK which primary corrects only the cylindrical component of the refractive error.11
However it can lead to flap complications like buttonhole, free cap and also to graft dehiscence. The use of PRK may lead to stromal haze and loss of BCVA.5
Off the intraocular techniques the use of secondary IOL is preferred to IOL exchange as it is considered to be less traumatic. The technique of implanting two IOLs together (piggybacking) was first described in 199312
where it was used to correct hyperopia in microphthalmos. Since then the method of implanting a second IOL (piggyback or add on IOL) in pseudophakic eyes is becoming increasingly popular. The use of piggyback IOLs to correct post PK refractive error was first described by Gayton et al
In their series of seven patients, there was an improvement in the total mean deviation spherical error from 3.41 D prior to surgery to 0.98 D afterwards. Since then Paul et al7
reported six eyes that underwent piggyback IOLs where the mean spherical equivalent reduced from −8.05 D preoperatively to −0.94 D postoperatively with no complications. Nuijts et al14
reported the largest series on the use of toric iris clip AC IOL (Artisan, Ophtec, Groningen, The Netherlands) for the correction of post PK astigmatism. Spherical equivalent was reduced from −4.90 ± 5.50 D before surgery to −0.96 ± 0.86 D at final follow-up. The endothelial cell loss was 7.6 ± 18.9% at 3 months and 16.6 ± 20.4% at 1 year. Although the visual outcomes are excellent, this rigid PMMA lens requires a large 5.3 mm incision. Such an incision after PK can lead to an unpredictable biomechanical response of the corneoscleral tissue to the incision and a greater variability in surgically induced astigmatism may be seen.
Park et al9
were the first to describe the use of a toric piggyback IOL to correct post PK astigmatism. They used a toric plate haptic IOL (Starr IOL, Vision Pharmaceuticals, Macclesfield, Cheshire, UK) through a 2.8 mm incision in a 72-year-old female who although had excellent visual outcome went on to develop corneal graft failure secondary to endothelial rejection 14 months after the piggyback procedure. As specular microscopy was not performed it is unclear whether this patient was at risk of graft failure.
The other previously reported complications of piggyback IOLs include interlenticular opacification and hyperopic shift.13 15
These complications can be avoided by using a acrylic IOL and by placing the second lens in the ciliary sulcus.
The Sulcoflex is a hydrophilic acrylic injectable IOL with undulating haptics and posterior 10 ° haptic angulation which provides excellent rotational stability (). It has an overall length of 13.50 mm with 6.50 mm optic. The lens is supplied in a 0.9% saline solution in a pouched blister pack and is injected using a disposable soft tipped injector. The drawback of the current model is that the maximum cylindrical correction is only up to 6 D. However we are led to believe that the manufacturer is currently working on higher cylindrical corrections. This initial report suggests that this new sulcus fixated injectable toric IOL seems to provide excellent visual and refractive outcomes with good rotational stability. However a larger cohort and longer follow-up is necessary to assess the long-term effect of this lens.
- Secondary toric IOL implantation is a new modality to treat post PK astigmatism.
- Injectable, sulcus fixated ‘add on’ toric lens can be effective treatment option to correct post PK astigmatism in pseudophakic eyes.
- Newer model toric IOL's are currently available to treat high cylindrical corrections.
- Long-term studies are required to monitor the corneal endothelial cell loss following such procedures.