Metals and plastics as functioning replacements are becoming an important and interesting development in modern surgery. Attempts to substitute chemically inert materials for defective organs or parts of organs were made in early medical history, but only in the past 20 years have these efforts met with any consistent success. It is interesting that eye surgeons were among the first in this field, although the size and delicacy of the usable structures in the eye would seem inconsistent with such work.

An important basic problem in the development of implants is the retention in tissues of the “incompletely covered foreign body.” This was first described and studied (for the past 15 years) in eye tissues. The concept of the incompletely covered foreign body has application in nearly every field of surgery.

Previously, it was believed that, for a would to heal, like epithelial cells must meet and join like cells. With the plastic artificial cornea it has now been shown that a wound can heal and create a barrier to bacteria and fluids with epithelial cells ending at a connective tissue barrier. The principles making possible the retention in tissues of the incompletely covered foreign body are discussed.

The utilization in tissues of the post-enucleation movable implant and plastic artificial cornea is described, and the uses of methyl methacrylate, silicones, Teflon, and hydrophilic polymers as related to the implantation of plastic artificial corneas, retinal detachment surgery, glaucoma drainage tubes, the repair of bony defects, replacing the vitreous of the eye, and substitution for the eye's crystalline lens are reported. Also mentioned are the problems which are encountered in implant material and fabrication.

The possibilities of the incompletely covered foreign body, especially in other branches of surgery, are pointed out.