New corneal inlay technology seems promising, but long-term results should be carefully monitored, reports Roibeard O h'Eineachain
There is as yet no clear answer regarding the longevity of new corneal inlays for presbyopia, as past experience has shown that visually significant complications can take years to occur, according to Béatrice Cochener MD, PhD, University of Brest, France.
“The current limitations with inlays are the short follow-ups. It is too soon to assume perfect bio-tolerance of the materials,” she told the 21st ESCRS Winter Meeting in Maastricht, The Netherlands.
She pointed out that some serious complications with the first hydrogel corneal implants for hyperopia did not occur until six years after surgery. With these first-generation inlays, late haze and deposits occurred in more than 80% of eyes and around half of patients required explantation of the implants within the first five years.
The haze deposits and corneal necrosis that occurred with the implants appeared to be related to postoperative inflammation around the implant. And although the complications can be modulated through the use of a tapered topical steroid regimen, the scars may be irreversible, but most often they do not result in long-term visual acuity disturbances.
The current intracorneal inlays which are indicated for presbyopia include the KAMRA Inlay (AcuFocus, Irvine, California, USA) which uses the pinhole effect, the Flexivue Microlens (Presbia, Irvine, California, USA) bifocal corneal inlay, and the Raindrop Near Vision Inlay (ReVision Optics, Lake Forest, California, USA), which reshapes the cornea.
They are composed of a soft material in order to easily conform to the cornea. Long-term studies out to five years have shown promising safety and efficacy outcomes, with no severe corneal complications; however, patients were monitored closely in these controlled trials. When a patient was explanted in these studies, the patient returned within one line of best-corrected distance vision from their preoperative measurements.
Depth of implantation appears to be a factor in the development of late haze. There is some evidence that the complication is less likely for the Raindrop inlay when implanted at 30% or greater central corneal depth. The KAMRA and Flexivue inlays fare best when implanted at about 200 microns or deeper in the cornea.
Dr Cochener noted that the age-group receiving the implants are at an increased risk of ocular surface dryness. Changes in corneal shape and the transection of corneal nerves during surgery can exacerbate the condition. Therefore, dry eyes should be carefully screened preoperatively and aggressively treated after surgery.
Decentration of the implants should be treated at an early stage. In the case of the Flexivue and Raindrop inlays, this is less of a problem than for the KAMRA inlay, which depends on perfect centration for optimal effect. When replacing an inlay, an interval between explantation and implantation of a new inlay can diminish the imprint of the initial inlay, she advised.
The new implants have an explantation rate of around 10%. Refraction following implant removal is generally within 1.0D of preoperative values. Reasons for implant removal include lack of effect, loss of effect, or most commonly progressive treatment-resistant haze.
Unlike other refractive procedures, inlays are foreign bodies implanted into the cornea. Implanted patients should be closely monitored every six to 12 months so that complications are diagnosed and addressed early. Drastic changes in vision, refraction, topography, patient satisfaction, or inlay appearance (slit lamp, optical imaging) are clinical red flags that require treatment. In treatment-resistant cases, explantation should always be considered.
“Corneal inlays are another technology we can offer our presbyopic patients, but vigilance should be practised to monitor for long-term complications,” added Dr Cochener.
Béatrice Cochener: firstname.lastname@example.org