Structural basis of contraction in vitreal fibrous membranes.

A combined ultrastructural and immunofluorescent study was conducted on experimentally induced fibrous membranes in the vitreous of adult rabbits. Autochthonous tissue cultured fibroblasts were injected into the mid-vitreous of one eye of each of 25 rabbits. The animals were monitored routinely with an ophthalmoscope and slit-lamp and were killed at various time periods between 5 minutes and 6 months. Appropriate tissue was taken for light microscopy, transmission electron microscopy, scanning electron microscopy, and indirect immunofluorescence. With this model we were able to show that the contractile elements in fibrous membranes are probably modified fibroblasts called myofibroblasts which are most abundant 3 to 6 weeks after injection. This is the time when retinal detachment usually occurs. It is our impression that, as traction membranes develop, there is not so much an increase in the contractile elements of the constituent cells as a rearrangement of the existing cytoplasmic microfilaments into compact highly organised bundles called stress cables. The behaviour and ultrastructural characteristics of intravitreal fibroblasts compare with the action of fibroblasts in the healing of wounds.