Chapter 3 - ophthalmic viscoelastic devices (OVD)
There are two basic categories of ophthalmic viscoelastic devices (OVD): [view video]
[click on image for larger view]
Different jobs demand different OVDs
1. Maintain space: | e.g. AC during rhexis | cohesive best |
2. Create space: | e.g. Creating sulcus | cohesive best |
3. Sealing off: | e.g. Sealing capsular tear | dispersive best |
4. Coating: | e.g. Protect corneal endothelium | dispersive best |
Removal of OVD
Removal |
|
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 | Must completely fill AC |
Phaco | Goes away with first vacuum | Stays on endothelium |
IOL insertion | Easy to open/maintain bag | Hard to remove residual material |
0 Comments:
Post a Comment
Links to this post:
Create a Link
<< Home