Appendix 2 - Viscoelastic

Appendix 2
Viscoelastic

Two basic kinds:

Cohesive:	high molecular weight, high surface tension, eg: healon Big, bulky, and likes itself

Dispersive:	low molecular weight, low surface tension, eg: viscoat Smooth and likes to coat others

More of a continuum	Ocucoat Viscoat	Most dispersive

	Provisc Amvisc Amvisc plus Healon

	Healon GV	Most Cohesive

Different jobs demand different viscoelastics

1. Maintain space:	eg.	AC during rhexis bag during IOL insertion	cohesive best
2. Create space:	eg.	Creating sulcus presenting lens material	cohesive best
3. Sealing off:	eg.	Sealing capsular tear keeping iris fragment at bay	dispersive best
4. Coating:	eg.	Protect corneal endothelium lubricate cornea w/o asst.	dispersive best

Removal

Dispersive harder to remove but post op IOP spike less of a problem
Cohesive is easier to remove because of high surface tension

Surgical Step	Cohesive	Dispersive
Capsulorhexis	1) Easy to maintain deep chamber 2) Can suddenly lose a large amount of material through wound	1) Must completely fill chamber to maintain
Phaco	Goes away with first vacuum	1) Stays on endothelium 2) Attract particles to endothelium 3) increased risk of burn
IOL insertion	Easy to open/maintain bag Easy to remove material	Hard to remove residual material