Abstract
This study was undertaken to identify mechanisms of adhesion of intraocular lenses (IOLs) to the
capsular bag after cataract surgery and IOL implantation. It was also done to challenge the sandwich
theory presented for posterior capsular opacification (PCO): If the IOL is made of a bioactive material
it would allow a single lens epithelial cell layer to bond both to the IOL and the posterior capsule at
the same time. This would produce a sandwich pattern including the IOL, the cell monolayer and the
posterior capsule. The sealed sandwich structure would prevent further epithelial ingrowth. The degree
of bioactivity of the IOL could explain the basic difference in the incidence of PCO and capsulotomy
rates with different IOL materials.
The sandwich theory was put forward on the basis of a search for a keratoprosthesis material,
which would allow maximal adhesion of the prosthesis to corneal tissue. Titanium and glass-ceramic
coated titanium were found to develop better adhesion than poly (methyl methacrylate) (PMMA). The
adhesion of PMMA to the corneal stromal tissue was loose, and down growth of corneal epithelial cells
was seen around the prosthesis.
The differences between various IOL materials were first tested with rabbit corneal tissue
cultures. There was better adhesion of corneal tissue to soft, hydrophobic acrylate than to PMMA,
heparin surface modified (HSM)-PMMA, silicone or hydrogel IOLs.
To assess differences in protein adhesion to IOL surfaces, different IOLs were incubated for 24
hours with radioactive iodine labeled fibronectin. Soft hydrophobic acrylate (AcrySof®) showed the
highest binding of fibronectin, and the differences relative to all the other materials were significant
(p < 0.01-0.001), except to PMMA (p = 0.31).
The sandwich theory and the results with rabbit corneal tissue cultures and the protein adhesion
study in vitro were evaluated against the results found in pseudophakic autopsy eyes. Altogether, 70
autopsy eyes were analyzed. From 38 autopsy eyes containing PMMA, silicone, soft hydrophobic acrylate or
hydrogel IOLs histological sections were prepared from the capsular bag and immunohistochemical analyses
were performed for fibronectin, vitronectin, laminin and collagen type IV. A total of 152 specimens were
analyzed. From 32 autopsy eyes containing IOLs made of PMMA, silicone, acrylate or hydrogel, IOLs were
explanted from the capsular bag and immunohistochemical analysis was done on both sides of the IOLs for
fibronectin, vitronectin, laminin or collagen type IV. Soft hydrophobic acrylate IOLs had significantly
more adhesion of fibronectin to their surfaces than PMMA or silicone IOLs. Also, more vitronectin was
attached to acrylate IOLs than to the other IOL materials. Silicone IOLs had more collagen type IV
adhesion in comparison to the other IOL materials studied. In histologic sections a sandwich-like
structure (anterior or posterior capsule-fibronectin-one cell layer-fibronectin-IOL surface) was seen
significantly more often in eyes with acrylate IOLs than in PMMA, silicone or hydrogel IOL eyes.
These studies support the sandwich theory for posterior capsule opacification after
cataract surgery with IOLs. The results suggest that fibronectin may be the major extracellular protein
responsible for the attachment of acrylate IOLs to the capsular bag. This may represent a true bioactive
bond between the IOL and the lens epithelial cells, and between the IOL and the capsular bag. This may
explain the reason for clinical observations of less posterior capsular opacification and lower
capsulotomy rates with the soft hydrophobic acrylate material of AcrySof® IOLs compared to the
other IOL materials studied.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn951-42-5979-3 |
| Date | 04 May 2001 |
| Creators | Linnola, R. (Reijo) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 2001 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/0355-3221, info:eu-repo/semantics/altIdentifier/eissn/1796-2234 |
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