EFFECT OF SILICONE OIL COMPONENTS ON CORNEAL ENDOTHELIAL PASSIVE PERMEABILITY AND ION-TRANSPORT

Silicone oil currently employed as a retinal tamponade is a complex mi xture of monomeric to long-chain polymers, and different components ma y be responsible for corneal endothelial or retinal toxicity. This stu dy on the corneal endothelium had two aims. First, to identify which s pecific component of a linear series of low-molecular-weight compounds caused the greater permeability increase, because when given collecti vely in earlier experiments they increased endothelial passive permeab ility. Passive permeability changes were determined by in vitro measur ements of inulin and dextran permeability following 1 week of in vivo exposure to oil containing different additives. Permeability was found to be increased after three of four linear compounds varying in lengt h from 1 to 10 silicone atoms (MDM [octamethyltrisiloxane] to MD(10)M [hexacosamethyldodecasiloxane]) were added to purified silicone oil. T he linear series offers no individual candidate for maximal effect, su ggesting that there is either an interactive or concentration-dependen t effect when these compounds appear together at high concentration in an oil compared to being present individually. The second aim was to determine if previous observations on permeability and overt corneal c hanges using various additives could be explained by differences betwe en passive permeability increases alone versus passive permeability in creases coupled with ion transport inhibition. This was achieved by me asuring unidirectional bicarbonate fluxes in vitro after 7 days of in vivo exposure to oil plus additive. Passive bicarbonate flux was incre ased after exposure to a catalyst, a representative of the linear seri es (MD(10)M), and a cyclic series of compounds. Only the cyclic series also decreased active ion transport. A direct interaction between the se additives and corneal components may offer a better explanation for the differential effects of additives on corneal opacity rather than effects on permeability and/or ion transport.