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Cohesive OVD Dispersive OVD

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1 Cohesive OVD Dispersive OVD
OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Maintains space poorly Coats structures poorly Coats structures well Viscosity: High Viscosity: Low

2 Q Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Maintains space poorly Coats structures poorly Coats structures well Viscosity: High Viscosity: Low Before we start: In this context, what does OVD stand for? Ophthalmic viscosurgical device

3 A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Maintains space poorly Coats structures poorly Coats structures well Viscosity: High Viscosity: Low Before we start: In this context, what does OVD stand for? Ophthalmic viscosurgical device

4 Q Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Maintains space poorly Coats structures poorly Coats structures well Viscosity: High Viscosity: Low OK, start divvying (do these two simultaneously)

5 Q/A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Maintains space poorly Coats structures poorly Coats structures well Viscosity: High Viscosity: Low Molecular weight: High Molecular weight: Low Molecule Now these

6 Q/A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Maintains space poorly Coats structures poorly Coats structures well Viscosity: High Viscosity: Low Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short etc

7 Q/A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Maintains space poorly Coats structures poorly Coats structures well Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface

8 Q/A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Maintains space poorly Coats structures poorly Coats structures well Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low

9 Q/A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Maintains space poorly Coats structures poorly Coats structures well Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate

10 Q/A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Coats structures poorly Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly

11 Q/A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Coats structures poorly Maintains space well Maintains space poorly Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well

12 A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

13 Q Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low In the context of OVDs, to what does the term viscosity refer? Viscosity refers to how a substance responds to shear force With respect to OVDs, what two ‘shear force scenarios’ are we concerned with? Which intraoperative steps provide a ready example of each? --Zero shear: Capsulorrhexis --High shear: Phacoemulsification, or I&A

14 A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low In the context of OVDs, to what does the term viscosity refer? Viscosity refers to how a substance responds to shear force With respect to OVDs, what two ‘shear force scenarios’ are we concerned with? Which intraoperative steps provide a ready example of each? --Zero shear: Capsulorrhexis --High shear: Phacoemulsification, or I&A

15 Q Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low In the context of OVDs, to what does the term viscosity refer? Viscosity refers to how a substance responds to shear force With respect to OVDs, what two ‘shear force scenarios’ are we concerned with? Which intraoperative steps provide a ready example of each? --Zero shear: Capsulorrhexis --High shear: Phacoemulsification, or I&A

16 A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low In the context of OVDs, to what does the term viscosity refer? Viscosity refers to how a substance responds to shear force With respect to OVDs, what two ‘shear force scenarios’ are we concerned with? Which intraoperative steps provide a ready example of each? --Zero shear: Capsulorrhexis --High shear: Phacoemulsification, or I&A

17 Q Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low In the context of OVDs, to what does the term viscosity refer? Viscosity refers to how a substance responds to shear force With respect to OVDs, what two ‘shear force scenarios’ are we concerned with? Which intraoperative steps provide a ready example of each? --Zero shear: Capsulorrhexis --High shear: Phacoemulsification, or I&A

18 A Cohesive OVD Dispersive OVD OVD properties: Divvy ‘em up
Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low In the context of OVDs, to what does the term viscosity refer? Viscosity refers to how a substance responds to shear force With respect to OVDs, what two ‘shear force scenarios’ are we concerned with? Which intraoperative steps provide a ready example of each? --Zero shear: Capsulorrhexis --High shear: Phacoemulsification, or I&A

19 Cohesive OVD Dispersive OVD
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

20 Cohesive OVD Dispersive OVD
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

21 Molecule length: Short
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

22 Molecule length: Short
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

23 Molecule length: Short
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

24 Molecule length: Short
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

25 Molecule length: Short
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

26 Molecule length: Short
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

27 Molecule length: Short
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

28 Molecule length: Short
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

29 Molecule length: Short
Think of the OVD molecules as pasta. Cohesive OVD molecules are like spaghetti—very long. Dispersive OVD molecules are like macaroni—very short. Now consider serving spaghetti vs macaroni. Because spaghetti strands are long, they entangle with and adhere to one another. So spooning any tends to result in the removal of most of the spaghetti. In contrast, because macaroni are so short, they don’t entangle and don’t adhere to one another. Thus, repeated spoonings are needed to remove macaroni from a bowl. So it is with OVDs. Cohesives, with their long entangled molecules, tend to come out of the eye as a single glob, whereas the short-chained dispersives have to be removed piecemeal. In like fashion, the non-self-adhering dispersives do an excellent job coating intraocular structures, whereas their self-adherence renders cohesives unsuitable for this. OVD properties: Divvy ‘em up Cohesive OVD Dispersive OVD Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Self-adheres well Viscosity: Low Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Maintains space well Coats structures poorly Maintains space poorly Viscosity: High Molecular weight: High Molecular weight: Low Molecule length: Long Molecule length: Short Viscosity: High Self-adheres poorly Surface tension: High Surface tension: Low Easy to aspirate Difficult to aspirate Coats structures well Maintains space poorly Maintains space well Viscosity: Low

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