PHACO IN MYOPES

In patients with moderate to high myopia undergoing cataract surgery, steps taken to avoid intraoperative complications can help reduce the risk of postoperative complications as well, said Oliver Findl MD, Vienna Institute for Research in Ocular Surgery, Hanusch Hospital, Vienna, Austria.

“In these patients we not only have the problem of retinal detachments after surgery being much higher, but we also have a higher rate of intraoperative complications, especially among those in the younger age group, patients in their 50s, who have high myopia,” Dr Findl told a Young Ophthalmologists symposium at the 19th ESCRS Winter Meeting in Istanbul, Turkey.

Dr Findl cited a retrospective review involving 1,793 eyes of 1,547 patients which showed that the risk of rhegmatogenous retinal detachment by the 10th postoperative year was 4.9 times higher in eyes with an axial length of 24mm or greater than it was in shorter eyes.

“Posterior vitreous detachment (PVD) is the predisposing event to the development of a break and then a retinal detachment. Approximately 10 per cent of patients with a symptomatic PVD have retinal breaks or retinal detachments requiring immediate treatment," Dr Findl said.

The older the patient, the more likely they are to already have had a PVD, which reduces the risk of postoperative retinal detachment. But research suggests that over a third of younger patients will develop a PVD within the first three postoperative years after cataract surgery. Similarly, those with high myopia have a higher incidence of developing a PVD after cataract surgery. Recent research has shown that another risk factor for retinal detachment is the presence of an adhesion of the anterior vitreous face to the posterior lens capsule around the ligament.

During cataract surgery the risk of posterior rupture and vitreous loss is approximately twofold among myopic eyes with an axial length greater than 26mm than it is in normal eyes. That in turn can set the rhegmatogenous retinal detachment process in motion, Dr Findl noted.

“If you have capsule rupture during surgery, you will typically induce a PVD. And obviously if you have vitreoretinal adhesions, these will then cause breaks leading ultimately to retinal detachments. We know that the retinal detachment rate in eyes that have had a capsule rupture and vitreous loss during surgery is about 12 to 15 fold higher than in it is in eyes that do not have this complication,” Dr Findl said.

The particularly difficult nature of cataract surgery in highly myopic eyes is an important factor in their higher rate of intraoperative complications. One problem commonly contributing to that difficulty is lens-iris diaphragm retropulsion syndrome.

That occurs when the anterior chamber infusion displaces the lens-iris diaphragm posteriorly, because of the thin and stretched zonules and underdeveloped ciliary body common in myopic eyes. That in turn causes reverse pupillary block with a marked deepening of the anterior chamber, and a posterior bowing of the iris.

“If the pupillary block is not relieved in some way, the surgeon will have a very steep axis in which to work, and on a nucleus which, in a long eye, is already far back eye to start with,” he said.

In such cases, Dr Findl relieves the block by lifting the iris with a spatula, thereby creating some space between the iris and capsule and allowing the lens to come forward.

He noted that myopic patients often need some additional anaesthesia because of the greater discomfort the surgery causes them. Studies show that intracameral anaesthesia may be effective in that regard. A sub-Tenons block is another alternative and can be safely performed by placing the sub-Tenons cannula through a small opening in the conjunctiva, eliminating any risk of perforating the eye.

Preoperative checklist

Dr Findl said that he has a preoperative checklist that he uses in all his myopic cataract patients. First, he insures that the patient is thoroughly informed and cognisant of the risk of retinal detachment.

Second on the list is to decide on the planned refraction, which is not always emmetropia because some patients will want to continue reading without glasses.

Dr Findl said that he will compare the lens powers indicated by different formulas, usually the SRK T, Haigis, and the Holladay formulas, and try to find a good mix. If it is the second eye in which the patient is to undergo cataract surgery, the power of the IOL should be adjusted in accordance with any refractive surprise in the first eye.

Oliver Findl: oliver@findl.at