Chapter 3 - ophthalmic viscoelastic devices (OVD)

There are two basic categories of ophthalmic viscoelastic devices (OVD): [view video]

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Different jobs demand different OVDs

1. Maintain space:	e.g. AC during rhexis bag during IOL insertion	cohesive best
2. Create space:	e.g. Creating sulcus shift lens material	cohesive best
3. Sealing off:	e.g. Sealing capsular tear keeping iris away	dispersive best
4. Coating:	e.g. Protect corneal endothelium lubricate cornea [view video]	dispersive best

Removal of OVD

Removal

Dispersive harder to remove Short molecules don't stick together during I/A but short molecules create less post op IOP spike Cohesive is easier to remove Longer molecules stick together during I/A Longer molecules block the trabecular meshwork for big IOP spike

Adaptive OVD

• Properties of dispersive OVD at high shear rate (e.g. during phaco)


• Properties of cohesive OVD at low shear rate (e.g. during IOL placement)


• Very long fragile chain molecules that break with flow rate


• One product on market -- Healon 5


• Form anterior chamber, which will cause intraocular pressure problems if not removed.

Arshinoff Shell

• Phase I during CCC


• First place dispersive OVD
• Then place cohesive OVD just over lens
• Then dispersive is pushed up to coat endothelium
• As soon as phaco starts cohesive is aspirated and dispersive coating remains


• Phase II during IOL insertion


• First place cohesive OVD in the bag
• Then place dispersive OVD just inside wound to seal prior to IOL placement
• When IOL is inserted, dispersive helps to keep cohesive in place; bag formed
  

Properties of Cohesive & Dispersive OVDs During Key Steps of Phacoemulsification

Step	Cohesive	Dispersive
CCC	Easy to fill AC Can suddenly lose OVD through wound	Must completely fill AC Stays in AC
Phaco	Goes away with first vacuum	Stays on endothelium Particles can stick to endothelium Increased risk of burn
IOL insertion	Easy to open/maintain bag Easy to remove material	Hard to remove residual material

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