CORNEAL COMPLICATIONS

The best type of keratoplasty to use for treating an eye with corneal complications following refractive surgery depends on the type of complication, said Jose Guell MD, Autonoma University of Barcelona, Barcelona, Spain, in a keynote lecture at the 16th ESCRS Winter Meeting’s cornea day. “The logical approach, when you must consider keratoplasty, is to take out only the layers there that are diseased,†he added. The techniques a corneal surgeon might use in such cases range from a simple epitheliectomy – with or without the use of amniotic membrane – to a deep anterior lamellar keratoplasty (DALK) or a full thickness keratoplasty procedure. In some cases where the only damage is to the endothelium, a posterior lamellar keratoplasty procedure may be indicated, he said. However, the efficacy of each technique is not entirely clear since the amount of published studies on the topic is sparse, he added. Both corneal and lenticular refractive surgery approaches have the potential to cause damage to the cornea. Complications of corneal refractive surgery that require keratoplasty can include flap complications, corneal scars and ectasia. The main complication of intraocular surgery is persistent endothelial cell loss, such as can occur with anterior chamber phakik IOLs. Dr Guell noted that there are only a few refractive surgery complications where he would currently recommend superficial anterior lamellar keratoplasty. They include those cases where there is an anterior opacity with a low degree of topographic irregularity, since using a microkeratome for such procedures will not correct any such irregularities but mimic the irregular surface. Another indication for a superficial approach is any abnormality restricted to the LASIK flap, in which case he would recommend a lenticule substitution, he said. He noted that in a series of 12 eyes of 10 patients in whom he performed superior anterior lamellar keratoplasty with a microkeratome to treat complications after corneal refractive surgery, there was a mean reduction in best corrected visual acuity in about 50 per cent of the cases, although in 85 per cent of the cases uncorrected visual acuity improved. The post-keratoplasty complications included one case of epithelial rejection, which resolved with topical steroids, and one case of lamellar keratitis which resolved with topical steroids and antibiotics. “We had a number of cases with the residual hyperopia and astigmatism resulting in a low best spectacle corrected visual acuity. That is possibly because using this technique will leave some degree of anterior lamellar irregular corneal irregularity,†he added.

DALK most widely applicable

Dr Guell noted that DALK is his preferred technique for the majority of cases of corneal refractive surgery complications that require keratoplasty. “Dissection at Descemet’s or 75 microns pre-Descemet’s is my procedure of choice when keratoplasty is indicated and the endothelium is healthy, because we preserve the endothelium and visual quality and acuity are the same as with penetrating keratoplasty [PKP]. The endothelial cell loss is also much less with DALK as is the number of rejection episodes,†he said. The main contraindications to DALK are eyes where the health of the endothelium is in doubt and eyes with very thin, previously perforated corneas. The most common complications after DALK are perioperative perforation – with reported incidences ranging from zero to 17 per cent – and the formation of a double anterior chamber between the Descemet’s membrane and the endothelium after the surgery. “Sometimes you're not aware of the perforation until the part Descemet’s dissection is being performed, but we all need to be aware that in very thin postoperative corneas the rate of perforations is higher. The result is that sometimes we will have a double anterior chamber, although most of the cases are solved with time and/or the injection of air/gas in the anterior chamber. He added that injecting viscoelastic material directly rather than air beneath the stroma when performing the dissection with the “big-bubble†technique can reduce the chance of perforation and anterior chamber perforation because it is a slower and more easily controlled process. It also provides superior visualisation of the process, he said. Dr Guell recommended restricting the use of PKP to those refractive surgery patients whose complications damage the stroma and also damage or obscure the endothelium to a point where its status cannot be confirmed. Finally, Dr Guell noted that endothelial complications of refractive surgery have become more common in recent years because of problems with some models of anterior chamber phakic IOLs (angle supported). In such cases he said that he prefers DMEK rather than DSAEK in order to provide optimum visual outcome. In patients older than 55 years, simultaneous refractive lens exchange can enhance patient satisfaction in such cases, he added.