July 2009

 

CATARACT/ IOL

 

The difference between IOL injectors


by Matt Young EyeWorld Contributing Editor

   
IOL injectors are key components of cataract surgery, oval ones—as opposed to hexagonal ones—may help better ensure IOLs are unscathed when delivered to the anterior chamber Source: Robert H. Osher, M.D.

Clear corneal incisions, microincisions, and foldable intraocular lenses (IOLs) have allowed ophthalmologists to perform minimally invasive cataract surgery, reducing the potential for astigmatism and optimizing visual quality in refractive lens exchange. The quest to maximally reduce incision size, however, has not come without a fair share of trouble. “We have ... moved away from the relatively simple insertion of rigid PMMA lenses with forceps to a much more complex affair, in which soft silicon or acrylic lenses are either folded or rolled and are then injected,” according to a scientific report by Steven Harsum, M.D., Moorfields Eye Hospital, London “As a consequence of this increased manipulation, intraocular lenses are more prone to damage.”

The extent of such possible damage with hexagonal injectors, noted by Dr. Harsum in the journal Eye online in February 2009, is intriguing. Fortunately, technological innovation has allowed ophthalmologists to move away from hexagonal injectors and embrace oval injectors instead, which appear to have eliminated many of these problems. Dr. Harsum’s research is far from antiquated, however. It provides a good reminder of how small the ophthalmologist’s surgical world is, and—even with the latest advances—how brittle it can be without continuous oversight. An enlightening experiment Dr. Harsum analyzed nine Rayner C-flex (570C) IOLs (Rayner Intraocular Lenses Limited, East Sussex, England) (three each of high, middle, and low power) injected with a manufacturer-supplied hexagonal nozzle into a petri dish and the same nine types injected with a manufacturer-supplied oval nozzle. The C-flex is a single-piece, closed loop, non-vaulted IOL of hydrophilic acrylic material, Dr. Harsum noted. “When injecting lenses through the original injector with the hexagon-shaped nozzle and the small hard plunger, eight of nine lenses had identifiable surface abnormalities visible at high magnification, with both the operating microscope and the SEM,” Dr. Harsum reported. “All surface abnormalities were linear, on the posterior surface of the lens, and in the direction of injection.”

Only one lens showed no signs of abnormalities. Four had significant abnormalities, two had minor surface ones, and two had imprints or crease-mark appearances on the posterior surface. “At high power these surface abnormalities appear to be of three types: fine irregular wavy filaments, triangular surface abnormalities, with the apex nearer the leading haptic, and the base towards the trailing haptic,” Dr. Harsum reported. “These tended to curl as they lengthened and could break free to resemble foreign bodies.”

Meanwhile, the oval injector set of lenses demonstrated better structural integrity. “When the newer injector with its oval-shaped nozzle and larger compressible soft-tipped plunger was used, only one of the nine lenses was thought to have a visible surface abnormality under the operating microscope,” Dr. Harsum reported. “Scanning electron microscopy, however, revealed the three lenses to have very minor surface abnormalities with the occasional wavy filaments.”

Given this research and that of others, Dr. Harsum believes the shape of the injector tip is directly responsible for whether lens surface abnormalities are present or not. “One other study has described a similar phenomenon, whereby injections through a hexagonal tip caused the nozzle to fracture and linear posterior surface abnormalities to appear on the IOL optic, whereas injection through a round tip did not,” Dr. Harsum reported.

This study is also unique in eliminating other possible causes for lens abnormalities, including nozzle fractures, stress lines, and nozzle exfoliations. “To reinforce that our surface abnormalities were not onlays, we recalled five patients who were identified in our audit as having pronounced lens abnormalities visible at the time of surgery,” Dr. Harsum reported. “In all cases, the surface abnormalities were still present three months postoperatively.”

Finally, Dr. Harsum emphasized the importance of understanding and eliminating lens defects. “It is well known that lens defects may cause dysphotopsia, be more proinflammatory, and are associated with greater bacterial adhesion and should therefore not be taken lightly,” Dr. Harsum noted. Interestingly, Bjorn Johansson, M.D., Linkoping University Hospital, Linkoping, Sweden, said he has not used hexagonal injectors, but nonetheless has experienced something akin to scratches on hydrophilic acrylic IOLs using round or oval injectors. “I have also observed small linear deposits on hydrophilic acrylic IOLs that I use,” Dr. Johansson said. Dr. Johansson said he has discussed this phenomenon with other surgeons, who have had similar experiences. Borrowing an idea from an ophthalmologist colleague, Dr. Johansson explained, “Because the IOL is compressed when folded and rolled into the injector and passed through the opening of the injector, it could be that the water content of the hydrophilic IOL is squeezed out through the surface of the lens, and as it goes through, this creates linear marks.”

Dr. Johansson also suspects the lubricant—or the lack thereof if the injector is reused—may be a factor in how linear marks are created on such IOLs. “I think it is important to know that if you choose to reuse the lens with the injector if the first attempt is not successful, then the used injector might be behaving differently because the lubricant might be used up, so to speak,” Dr. Johansson said. Nonetheless, Dr. Johansson has found that such marks always disappear by day one post-op, and in his opinion, have no impact on visual performance. h

Editors’ note: Dr. Harsum reported no financial interests related to this study. Dr. Johansson has no financial interests related to his comments.

Contact information

Harsum: +44 20 7253 3411, harsum@doctors.org.uk
Johansson: bjorn.johansson@lio.se

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