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IOLs cause variety of tissue reactions, biomicroscopy study demonstrates
Cell behavior on IOL surfaces, observed in vivo, offers an objective evaluation of the biocompatibility of several foldable and non-foldable lenses.
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NAPLES — A study conducted at the University of Trieste used biomicroscopy to investigate the interactions between ocular tissue and the surfaces of different types of IOLs, giving a visual demonstration of how tissue response varies according to the lens material.
“There are two main types of cellular reaction to IOL implantation after cataract surgery,” said Daniele Tognetto, MD, author of the study, who spoke at the Italian Ophthalmologic Society meeting here.
“One is the inflammatory reaction, which is the eye’s attempt to eliminate any foreign bodies that have been introduced. At first, small, round or spindle-shaped macrophage-type cells appear on the anterior surface of the lens. They move around on the surface swallowing up bacteria, pigment and debris. They reach a maximum density 1 month after surgery, then progressively diminish until they disappear between the third and sixth month.”
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“One month after surgery, some larger, epithelioid cells may appear. They secrete enzymes in an attempt to decompose foreign bodies. Later they may merge with smaller cells to form giant, multinucleated cells. Having given up attempts to destroy the lens, they then try to isolate it from the ocular tissues,” said Dr. Tognetto.
The second type of cellular reaction comes from the lens epithelial cells, involving the anterior and, at a later stage, posterior capsule. Cell proliferation and migration may generate fibrosis, membrane formation over the IOL optics, posterior capsule opacification (PCO) and Elschnig pearl formation.
Both types of reaction indicate the degree of biocompatibility of the IOL material.
PMMA and silicone
PMMA, which is still widely used in intraocular implants, proved far less inert than was initially believed. Biomicroscopy observation on heparin surface-modified IOLs confirmed this assumption.
“During implantation, the IOL surface is sometimes accidentally scratched. On heparin-coated PMMA lenses, a small portion of the heparin layer is removed and the PMMA exposed. We have observed that in diabetic patients, where the cell reaction on the IOL surface is more intense, inflammatory cells accumulate deep within the scratches, where the PMMA is exposed,” said Dr. Tognetto. This finding confirmed the efficacy of the heparin treatment of the lens in reducing postoperative inflammation and improving PMMA biocompatibility, he said.
Silicone is known to have good biocompatibility. In Dr. Tognetto’s experience with the Allergan SI40NB IOL, biomicroscopy showed a reduced presence of inflammatory cells on the IOL surface from the initial days after surgery. “However, cell reaction on this type of material can be more intense in presence of pathologies which predispose to postoperative increases in the breakdown of the blood-aqueous barrier, such as pseudo-exfoliation syndrome, diabetes and uveitis,” Dr. Tognetto noted. “In these cases, we could observe the presence of giant cells near the iris and the proximity of posterior synechiae.”
When the capsulorrhexis margin lies over the IOL optic, silicone almost invariably produces fibrosis of the anterior capsule, he said. However, membrane formations are rarely observed.
Hydrophilic and hydrophobic acrylics
The high biocompatibility of hydrogel lenses is shown by the scarcity or absence of cells on their surfaces during the early days after surgery, but significant differences can be observed through biomicroscopy on the surface of different types of the same category of lenses.
“In most hydrogel IOLs we observed a proliferation of epithelial cells (Bausch & Lomb Hydroview H60M, Corneal ACR6D and HP58, CIBA MemoryLens, Bausch & Lomb EasAcryl, PMS E48500 and IOLTech Stabibag). They formed a membrane that extended from the capsulorrhexis margin to the lens optic. This growth was visible from the first week postoperatively, expanded during the following weeks and stabilized around the third month. With some types of hydrogel lenses we found a higher incidence of anterior capsule fibrosis, and again with others, fibroses and membrane growth were associated,” Dr. Tognetto explained.
Among hydrophobic acrylics, Dr. Tognetto found Alcon AcrySof “highly biocompatible.” In his experience, he said, the presence of cells on the surface of this material is very low. Some small, round or spindle-shaped cells may appear in the early postoperative period, but they are quite rare and sparse. Epithelioid or giant cells may appear in the case of pathologies that tend to provoke rupturing of the blood-aqueous barrier.
“Using these lenses the anterior capsule, when placed over the IOL optic, remains quite transparent and, in most cases, does not develop fibrosis, which is so common with other lens materials. No membrane growth takes place over the optics,” he said.
AcrySof IOLs have square-edged optics. This design was conceived to prevent the migration of epithelial cells from the equator to the posterior capsule, reducing PCO rates. However, the shape of the lens may not be the only factor in preventing opacification.
“After implantation, the epithelial cells under the anterior capsule are in direct contact with the IOL. The processes of fibrosis and cell proliferation could therefore take place irrespective of the lens shape. I believe that the material of the lens may be an important inhibitor of epithelial cell proliferation,” Dr. Tognetto said.
For Your Information:
- Daniele Tognetto, MD, can be reached at Ospedale Maggiore, 34129 Trieste, Italy; tel./fax: +(39) 040-772449; e-mail: tognetto@univ.trieste.it. Dr. Tognetto has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.