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NUERNBERG - Intracorneal lamellar implants may become a viable option for hyperopia correction up to +6.0 D but more clinical experience is needed to perfect their use, reported Michael Knorz MD at the Congress of German Ophthalmic Surgeons.

Dr Knorz implanted 22 Permavision intracorneal lenses (Anamed Inc) as part of a prospective multicentre study. Since 1999, 106 eyes in 16 centres have received the implants.

The average age of patients was 46. The mean preoperative visual acuity was 3.8 D and the mean cylindrical refraction 0.5 DT.
Dr Knorz implemented the Amadeus microkeratome which produces a flap thickness of 180 microns, a flap diameter of 9.5 mm and a six o'clock hinge.

He reported that the thicker flap produced by the Amadeus microkeratome, compared to the Hansatome, allowed him to remain at a safe distance from the corneal surface and thereby avoid superficial trophic corneal complications.
He performed the cut from the 12 o'clock to the six o'clock positions. The advantage of cutting in this direction was the creation of an inferior hinge. This avoided a decentration of the implant and would keep it from slipping out from below, he explained.

After the lenses were transferred into the corneal stroma, Dr Knorz waited several minutes to allow the implants to settle. He then flipped the corneal lamellae back into place.
At one week following surgery, all 106 patients appeared for follow-up monitoring. Further examinations took place between two and six months time. Dr Knorz saw 16 of the 45 patients examined worldwide at six months postoperatively.
The researchers calculated a mean postoperative visual acuity of 0.7 D at six months revealing a slight undercorrection.

There was no indication of induced astigmatism since the cylindrical refraction was basically unchanged postoperatively.
A total of 67% of the study participants had visual acuity within 0.5 D of the target and 84% were within 1.0 D.

Dr Knorz reported decentration by 0.5 mm or more in four of the 16 implantations he performed. These occurred in the early postoperative stages. Decentration frequently results in irregular astigmatism. He surgically removed two of these implants.
A white lipid-like deposit along the edges of the implants was observed in all patients monitored. There was no reaction to steroid treatments.
Although most of the patients manifesting these vague whitish deposits had no symptoms, two lenses needed removal due to the deposits. Dr Knorz is still unsure of their exact nature.

The stability of the procedure is not unlike LASIK. There is an initial phase of epithelial healing with an associated "overshoot" that results in a slight myopia.
The regression of this epithelial growth over the next few months generally leads to emmetropia and sometimes slight hyperopia.
He was not satisfied with the predictability of the implants since many patients reportedly lost greater than two lines of BCVA. Only a few patients gained lines of vision.

Ten patients reported halos, particularly at night. Four cases were mild while six were substantial. Dr Knorz explanted the lens in one especially irritating case. The 6.0 mm implants appeared to reduce the incidence of halos, he noted.
Halos are a complication well known to LASIK in the higher hyperopia cases. Dr Knorz pointed out that the halo effect experienced by LASIK patients cannot be reversed.
In this case, removal of the intracorneal implant alleviated the halo effect and the preoperative acuity values were regained within only a few days.

Compared to LASIK, the Permavision lens ensures increased precision in high hyperopic cases. LASIK is limited to very low hyperopes and myopes.
As such, myopia correction is close to 90% glasses-free with LASIK while intracorneal implants provide only an unsatisfactory 60% to 70%.

"In my opinion, the Permavision intracorneal lamellar implant offers a more logical way to correct hyperopia than with the use of ablation. Tissue does not need to be removed in hyperopes. What they need, in fact, is a central elevation and these lenses provide just that.

"The complication rate we observed in this Phase I-II trial is still too high for the general clinical introduction of this procedure. We could not expect to see as refined results as with LASIK or other procedures we have been improving and learning from over time. We have yet to discover the ideal operative technique and lens diameter," Dr Knorz said.
The Permavision lens is a hydrogel lens with 78% water content. It has a 1.376 refractive index much like the corneal refractive index and is available in 5.0 mm or 6.0 mm diameters.

The central thickness of the lens varies between 25 to 60 microns which is relatively thin. The lens lies on a fine spoon-shaped plate from which it is transferred to within the cornea.
Although experiments with intracorneal implants date back as far as the 1950s when surgeons implanted glass lenses, it was the advent and accessibility of highly permeable, soft and gel-like substances that incited the renewed enthusiasm of ophthalmic surgeons.

There are currently several different intracorneal implants undergoing FDA approval studies.

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