Characteristics of eye protheses materials
Wettability - Comparison between glass and plastic (PMMA)


The illustrated photographs have been published thanks to the kind permission of Dr. med. F. Härting [1].

Images 1 - 3: Flow properties of watery liquids on a glass surface: You see the immediate, natural spreading of the fluorescent liquid on the glass surface. This is known as "hydrophilic" behaviour. When the prothesis is inserted, the tears can form a gliding film between the prothesis and the lids or the conjunctiva respectively. This supports the moveability of the artificial eye and the closing of the lid and further reduces all the friction.

Images 4 - 6: Flow properties of watery liquids on a plastic surface: The deposited, fluorescent liquid remains in place in the shape of a drop. It does not spread well over the surface. A continuous film of tears can hardly form on an applied plastic prothesis. This rather promotes 'mechanical' irritations of the conjunctiva.

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Discussion:
Glass has "hydrophilic" properties, while plastic protheses (PMMA) roll away due to the "hydrophobic"
properties of human tears. The lack of shortage of available natural lubricant between the prothesis
and the conjunctiva frequently leads of "mechanical" irritations. This is why many people wearing
plastic prostheses must regularly apply drops of "artificial tears".





Copyright © 1999 Swiss Institute for Artificial Eyes, CH-Lucerne. Reprinting subject to the permission by the author.