PSEUDOPHAKIA

Pseudophakic patients might seem good candidates for presbyLASIK, which creates a multifocal cornea to restore near vision. However, eyes with monofocal intraocular lenses (IOLs) may require more near vision add than corneal ablation can provide, particularly since pupils in elderly patients may be too small for a multi-zone multifocal cornea to properly function, Thomas Kohnen MD, PhD told Refractive Surgery Day at the 2014 American Academy of Ophthalmology annual meeting in Chicago.

“Therefore we think it is questionable to treat pseudophakic patients with presbyLASIK, even though the problems of presbyopia progression and future IOL calculation no longer occur,” said Prof Kohnen, of Goethe University, Frankfurt, Germany.

Also, very little data on presbyLASIK in pseudophakic patients is available, though a few cases have been performed, he added.

Indeed, some studies suggest that five-seven per cent or more of patients undergoing presbyLASIK lose two or more lines of best corrected distance vision, raising safety questions for any population, Prof Kohnen noted. However, the procedure is still developing and appears to be improving as treatment algorithms are adjusted.

MULTIFOCAL APPROACH

Prof Kohnen defines presbyLASIK as multifocal corneal surgery, as opposed to monovision, which combines monofocal corneal surgery of different power in each eye. PresbyLASIK always
uses monocular multifocality and thus simultaneous imaging of two or more foci on the retina.

Early theoretical studies showed a central corneal add zone increases visual acuity at shorter distances, Prof Kohnen said. It also increases spherical aberration, resulting in more light reaching the retina at a point (Ortiz D et al. J Refract Surg. 2007;23:39-44). More recent research also suggests induced corneal wavefront aberrations from PresbyMAX treatment with the Schwind Amaris laser also increases both uncorrected and distance corrected monocular near vision.

Multifocal corneas can be shaped with a central near add with peripheral distance focus, or vice versa, and both have been tried using various modalities, Prof Kohnen said. Lab science suggests a central steep island producing a near add is most effective. However, it is highly dependent on centration.

Systems including the PresbyMAX now make it possible to surgically reverse the central add, Prof Kohnen noted. “But we have to look at this critically. When we have this cornea there is nothing we can do with correcting it with glasses postoperatively,” he said.

In reviewing presbyLASIK for use in Germany, Prof Kohnen and colleagues found several articles showing an improvement in uncorrected near and distance vision. However, a closer look also often revealed loss of distance corrected visual acuity.

Prof Kohnen’s ongoing unpublished research on phakic patients undergoing PresbyMAX, with -0.75 micro monovision in the non-dominant eye, shows a similar pattern. Six-month results from the first 15 patients show increases in uncorrected near vision, with 60 per cent of dominant eyes and 87 per cent of non-dominant eyes at 20/25 or better at 40cm after surgery, up from seven per cent and zero per cent before surgery. Three-quarters of dominant and 80 per cent of non-dominant eyes gained three or more lines.

However, uncorrected distance visual acuity was worse than corrected visual acuity after surgery, with 100 per cent at 20/25 corrected before and 50 per cent 20/25 uncorrected afterwards. Even more concerning, 46 per cent lost one or more line of best corrected distance vision, with 20 per cent losing two or more lines in the dominant eye, and 26 per cent one line and 20 per cent two lines in the non-dominant eye. “Basically we are losing vision here,” Prof Kohnen said.

On the other hand, vision improved over time with patients more satisfied at six months than one month after surgery. Refractive astigmatism also increased after surgery in some cases. This may be due to irregularities in ablation in the central zone as noted on topography. All these procedures are evolving so this can be changed in the future, Prof Kohnen said.

On a scale of one to six, with one best, patients rated distance vision worse, in the three to four range for activities such as watching TV and night driving, but in the two to 2.5 range for near tasks such as cooking and reading newspapers. Overall, 80 per cent said they would have the surgery again and would recommend it to a friend.

Regarding use of presbyopia in pseudophakic patients, Prof Kohnen noted no reports in the literature and is using it himself only on phakic patients. Patients with monofocal IOLs need a full add of up to 2.5 dioptres, and this might be difficult to achieve using corneal ablation given the small pupils of many older patients.

Thomas Kohnen: kohnen@em.uni-frankfurt.de