SEM of IOL surfaces reveals gentler impact of injectors

Forceps caused irreversible alterations to the surface of acrylic lenses, possibly leading to postoperative complications.

ByMichela Cimberle

At various magnifications, SEM showed the profile of the edge-loop junctions appeared morphologically unaltered.
The forceps were tightened very delicately and progressively until the lenses were folded correctly along the 6-to-12 o’clock axis.

At a low magnification, five of the nine lenses showed linear and parallel alterations in the area compressed by the forceps.

At high magnification, these irregularities appeared as marks and scratches in the profile of the optical disk. The edges and the edge-loop junctions did not show alterations after folding.

FLORENCE – Making the right choice among different IOL folding systems may be crucial in preventing complications and in determining the long- term optical performance of lenses.

Scanning electron microscopy (SEM) was used to evaluate the optic surfaces, edges and edge-loop junctions of two types of acrylic IOLs before and after folding, and the effects of the two standard folding methods – injector and forceps – were compared. The study was conducted here by Rita Mencucci, MD, and colleagues.

“Recently, acrylic has met with considerable success. It has been calculated that it is used in about 50% of IOLs. Acrylic helps in making thinner lenses with large optic disks, which are flexible, easy to fold and distend well in the capsule,” said Dr. Mencucci, an assistant clinical professor of ophthalmology at the University of Florence.

“Nevertheless, these lenses are more fragile and thus more susceptible to marking and scratching than silicone lenses. And we should not underestimate how much these alterations of the integrity of the surface may influence postoperative inflammation, anterior and posterior capsule opacification and visual quality.”

Before folding

SEM was used to examine 12 Sensar AR 40 IOLs from Allergan and 6 AcrySof MA60BM lenses made by Alcon.

The Sensar lenses are characterized by an optical surface made of soft foldable transparent acrylic with a UV covalent-bond absorber. Relative density is 1.16 and the refractive index is 1.47 at 25° C. The PMMA loops have a modified C configuration.

The AcrySof lenses are made of a methacrylate acrylate copolymer with a UV filter. The refractive index is 1.55. The loops are equally of PMMA, with a modified C design.

The Unfolder Sapphire Implantation system was used to fold the several Sensar lenses and results with the Unfolder were compared to folding of both types of lenses using folding forceps J2188.20 and J2186.2 by Janach.

After washing with balanced salt solution (BSS), the lenses were attached to the sample holder by using two-sided adhesive tape. They were then covered with 15 nm-thick metallic conductive film, using the sputtering technique. A Polaron SEM coating system with a palladium gold anode was used. The prepared samples were observed at SEM (515 Philips); acceleration voltage was 15 to 18 kV and magnification varied from 1.1 E1 to 4.2 E2.

After folding

Five Allergan IOLs were investigated after folding with a cartridge and an Unfolder Sapphire hand piece for 20 seconds at 20° C.

“We coated the cartridge with a drop of Healon viscoelastic, then inserted the lens into it with the aid of straight clamping forceps. The cartridge was closed and the lens was held there for 10 seconds. We then inserted the cartridge into the hand piece and the lens was gently pushed out according to the manufacturer’s instructions,” Dr. Mencucci said.

At various magnifications, SEM showed no significant alteration of the optical surface of these lenses. Also the profile of the edge-loop junctions appeared morphologically unaltered (figure 1).

A total of nine lenses, five Allergan and four Alcon, were analyzed after folding with acrylic forceps for a total of 20 seconds at 20° C. The forceps were used following the manufacturer’s guidelines.

“We inspected the forceps to ensure that the tips were meticulously clean and in perfect condition to prevent damage to the surface of the lenses. We used a pair of straight clamping forceps to remove the lenses from their original packaging, and each lens was removed by grasping the middle end portion of the loops,” Dr. Mencucci said.

The lenses were bathed in BSS and coated with a drop of Healon viscoelastic, then correctly positioned in the folding forceps.

The forceps were tightened very delicately and progressively until the lenses were folded correctly along the 6-to-12 o’clock axis. They were maintained in this position for 10 seconds. Each lens was then grasped by the holding forceps for 10 seconds.

“At a low magnification, five of the nine lenses (three Sensar and two AcrySof) showed linear and parallel alterations in the area compressed by the forceps,” she said (figures 2 through 4).

“At high magnification, these irregularities appeared as marks and scratches in the profile of the optical disk (figures 5, 6). The edges and the edge-loop junctions did not show alterations after folding.

Fewer problems with injectors

“It was evident that the IOL injector caused fewer problems in comparison with the acrylic lens forceps. Forceps were shown to cause irreversible alterations on the surface of acrylic lenses, which may predispose the eye to inflammation, cause cellular adhesion and secondarily facilitate posterior capsular opacification,” Dr. Mencucci said.

“We do not know how much influence these alterations can have on the patient’s visual quality once the IOLs are introduced into the eye. Further studies will have to be made to evaluate this aspect. Nevertheless, the peripheral interruption of the optical surface can cause diffraction of light and dazzling, especially during nocturnal mydriasis,” she said.

The injector, on the other hand, is gentler with the lens and causes no alteration of the surface, she noted. It also protects the lens during its passage from the nonsterile outside environment to the inside sterile anterior chamber through the corneal incision.

“When using forceps, the lens is uncovered and is more exposed to contamination as it will most probably come into contact with the conjunctiva,” she said. “Lastly, the folding-injection system has a more homogeneous distribution of pressure on the lens itself. Greater standardization of IOL insertion procedures is therefore possible.”

For Your Information:

Rita Mencucci, MD, can be reached at Università degli Studi di Firenze, Clinica Oculistica II, Viale Morgagni 85, 50134 Firenze, Italy; +(39) 055-411-765; +(39) 055-437-7749; e-mail: oculist@unifi.it. Dr. Mencucci has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned.

Alcon can be reached at 6201 South Freeway, Fort Worth, TX 76134 U.S.A.; +(1) 817-551-6828; fax: +(1) 817-241-0677.

Allergan can be reached at 2525 Dupont Drive, Irvine, CA 92612 U.S.A.; +(1) 714-246-4297; fax: +(1) 714-246-5913; Web site: www.allergan.com.