Intraocular lens material evaluation by iris abrasion in vitro: a scanning electron microscope study

Prosthetic posterior chamber intraocular lenses can abrade the iris pigmented epithelium, resulting in pigment dispersion, callus formation, and iris adhesions. To evaluate iris abrasion from intraocular lens materials, we developed an in vitro test and studied three materials: polymethylmethacrylate (PMMA), silicone, and PMMA surface-modified by covalent binding of a hydrophilic polymer (surface-modified PMMA). Each lens was rubbed 1,000 times on the posterior iris of pigmented rabbits using a total force of 0.5 gram. Scanning electron micrographs of the abraded irides were scored using a subjective, nonparametric numerical scale. Polymethyl-methacrylate lenses removed iris epithelium completely, exposing underlying connective tissue. Silicone lenses damaged an area longer and narrower than the PMMA lens and also exposed connective tissue. Surface-modified PMMA lenses caused only slight surface damage, including flattening or breaking of protruding suspensory ligaments. The test conditions used cannot precisely mimic prolonged lens implantation in living subjects. Nevertheless, the results indicate that iris-lens interaction may be reduced in vivo by using a surface-modified PMMA lens. This hypothesis should be further verified by animal implantation studies.

Fibronectin in corneal wound healing

Fibronectin is an extracellular structural protein with the unique ability to bind to both cells and collagen. It plays a major role in the development of the cornea. The universal appearance of fibronectin within 8 hours of corneal wounding has promoted major interest in its wound healing properties. The early clinical evidence for fibronectin treatment of recurrent corneal erosion and certain forms of keratitis sicca is strong. The current major problem preventing commercial use is the antigenic nature of fibronectin derived from separate species. Human pooled fibronectin has been suggested as a commercial source of this ubiquitously occurring protein.

Cytoplasmic origin of an intranuclear DNA virus (duck plague virus)

Electron microscopic and autoradiographic studies have revealed that the assembly and maturation of duck plague virus (DPV, an intranuclear DNA virus) occur both in the nucleus and in the cytoplasm. A dense cytoplasmic matrix (tentatively called viroplast) is the basic organelle in which the assembly of nucleocapsids occurs. At the early stage of virion maturation, dense particles, approximately 40 nm in size, appear and become assembled nucleocapsid structures later on. As capsids become mature, they obtain a diameter of 95-105 nm. The viroplast matrix gradually decreases in size, and a loose structure appears inside as the nucleocapsids increase in number. When viroplast has almost disappeared, nucleocapsids become abundant, regularly arranged around the cytoplasmic vacuoles. They bud into these vacuoles, thereby acquiring their envelopes. These nucleocapsids differ from those found in the nucleus both in morphology and in distribution. Electron microscopic autoradiography has shown that there is a huge amount of DNA in viroplast. DNA for the assembly of the nucleocapsids in the cytoplasm is derived from the very viroplast.