|Viscoelastics can be divided
into 2 types:
There is a spectrum ranging
from most cohesive to most dispersive.
high molecular weight, high surface tension, for example Healon. It tends
to be big and bulky and do not coat tissue.
Dispersive with low molecular
weight, low surface tension, for example: Viscoat. It is smooth and likes
to coat others
Viscoat and Ocucoat (most
dispersive)....Provisc...Amvisc...Amvisc plus...Healon....Healon GV (most
Advantages and disadvantages.
Cohesives best for maintaining
anterior chamber, capsulorrhexis and creating space. Easy to remove because
of high surface tension. Can lose a large amount through wound during capsulorrhexis
if the wound is open. Tend to go away with the first vacuum. Do not protect
Adhesives best for protecting
the corneal endothelium, sealing capsular tear and keeping iris at bay.
Do not maintain space well. Attract particles to endothelium and increased
risk of burn.
Note: Both cohesive
and dispersive can be used together during cataract surgery. In the 'soft
shell' technique, dispersive is first injected to coat the endothelium
and cohesive injected next to fill the anterior chamber. This improves
endothelium protection in cornea with low endothelium count.