Preoperative slit-lamp appearance (left) of the right cornea of a 31-year-old patient showing endothelial decompensation observed three years after implantation of an iris-supported phakic IOL (iris-claw style). Two years after a procedure (including removal of the phakic IOL, phacoemulsification, implantation of a posterior chamber IOL in the capsular bag, pupilloplasty and DSAEK), the right picture shows a perfectly clear cornea with a perfectly attached DSAEK graft and a round pupil. Vision was 1.0
Massimo Busin MD
Corneal refractive surgery generally poses little risk to the corneal endothelium, but phakic intraocular lenses (IOLs) currently in use are associated with a minor risk of corneal decompensation, according to Massimo Busin MD, Villa Serena Forlì Hospital, Italy.
“In general, with corneal refractive surgery we have some endothelial cell loss (ECL) but no progression and no corneal decompensation,” Dr Busin said in a keynote lecture at a Cornea Day session during the 21st ESCRS Winter Meeting in Maastricht, The Netherlands.
In the early days of refractive surgery, the delicate nature of the corneal endothelium was poorly understood. In fact, the first type of radial keratotomy (RK) developed in the 1940s involved radial incisions on both the anterior and posterior surface of the cornea.
The treatment often led to corneal oedema and decompensation. However, the mean time between the procedure and the development of bullous keratopathy was around 27 years, which highlights the follow-up needed to judge a procedure’s safety.
RISK FACTORS
With a more familiar type of RK, central ECL was only 3-10% in the 10-year-long PERK study involving patients who underwent the procedure from 1982-1983. Risk factors for ECL included increased number of incisions and smaller optical zones, he said.
Despite some theoretical dangers of corneal photoablative procedures such as photorefractive keratectomy (PRK) and LASIK, overall the evidence suggests that excimer laser refractive surgery does not cause progressive loss of corneal endothelial cells.
And although an early study by Prof Ioannis Pallikaris reported an ECL of 9-10% after LASIK or PRK for high myopia, most subsequent studies have not shown a progressive ECL.
A more recent study showed that the mean rate of ECL was the same among patients who underwent LASIK or PRK as it was in control eyes, 6.0% at nine years
(Patel et al, Arch Ophthalmol. 2009;127:1423-7). Different ablation frequencies also do not appear to differ in their effect upon the endothelium, and femtosecond laser LASIK flap creation appears to have little effect on the endothelium.
He noted that research shows that a residual stromal bed of 200μm or more prevents ECL following excimer laser photoablative procedures. A residual stromal bed of 250μm or more is currently recommended to avoid corneal ectasia.
NO SIGNIFICANT EFFECT
Even PRK plus mitomycin-C has no significant effect on the endothelium, although research has shown it can enter the anterior chamber. Dr Busin noted that, because of its anti-proliferative mode of action, mitomycin-C is unlikely to damage the naturally non-proliferative endothelial cells. Intracorneal inlays and intracorneal ring segments also appear to leave the endothelium without damage, even when explantation is necessary.
Perhaps the best evidence that LASIK and PRK treatment is not unduly harmful to the cornea is that, according to current Eye Bank Association of America (EBAA) guidelines, corneas that have undergone the laser photoablative procedures can be used as donor corneas for posterior lamellar keratoplasty.
He added that corneas with intracorneal ring segments can be used for Descemet’s membrane endothelial keratoplasty (DMEK), but not for Descemet’s stripping automated endothelial keratoplasty (DSAEK), because of the loss of integrity of the deep stroma. Instead, corneas that have undergone RK have been used successfully for ultra-thin DSAEK.
However, the story is different with regard to anterior chamber phakic IOLs, especially some of the now discontinued angle-supported models. Iris-supported IOLs have been involved in a much smaller number of cases of postoperative complications. Most studies show a slow rate of ECL, although cases of severe ECL occasionally occur with the lenses.
However, good visual recovery is possible for most patients through phakic IOL explantation, phacoemulsification, posterior chamber IOL implantation, and DSAEK.
Massimo Busin: mbusin@yahoo.com
