What is a tamponade?

“Tamponade” is defined as the use of a tampon, which itself is defined as “a plug or tent inserted tightly into a wound or orifice to arrest hemorrhage”. With regard to vitreoretinal surgery, tamponade agents are used to provide surface tension across retinal breaks, which prevents further fluid flow into the subretinal space until the retinopexy (photocoagulation or cryopexy) gives a lasting chorioretinal attachment.



Introduction to vitreous substitutes

Vitreous substitutes have been developed both as an intraoperative and as a postoperative tool for the surgical treatment of complicated vitreoretinal diseases. The effectiveness depends on the area of contact between the agent and the inner retinal surface, while displacing the aqueous from the retinal surface. Physical parameters influencing this property include-


(i) specific gravity

(ii) buoyancy

(iii) interfacial tension

(iv) viscosity


The choice of different intraocular tamponade agents depends on the

location of retinal break(s),

compliance of postoperative posture,

type of vitreoretinal disease(s), and

duration required for the tamponade



Characteristics of an Ideal Vitreous Substitute


1. Should mimicthe native vitreous

2. Have similar viscoelastic properties

3. Have similar refractive index and density

4. Easy to manipulate during surgery

5. Clear and transparent

6. Biologically and chemically inert

7. Hydrophilic and insoluble in water

8. Biocompatible and nonbiodegradable

9. Non toxic

10. Be able to maintain the normal IOP to support the ocular tissues in proper position

11. Allow movement of ions and electrolytes and maintain the concentration of certain substances (oxygen, lactic acid, and ascorbic acid)

12. Readily available at reasonable cost

13. Easy to store



Types of Vitreous Substitutes

Vitreous substitutes could be classified in different ways. A functional classification referred to as the surgical application is described in the literature:

(i) As temporary fillers of vitreous cavity during the surgical procedure to maintain the ocular tone;

(ii) As surgical tools themselves during different phases of vitreoretinal surgery, requiring a short intraocular permanence;

(iii) As a therapeutic tool left inside the eye after vitreoretinal surgery with different permanence time


There are three major categories of substitute based on a different classification according to their



molecular status –

1. Gases – most commonly used are air, sulfur hexafluoride (SF 6 ) and perfluoropropane (C 3 F 8 ).

2. Liquids – Silicone Oil (SO) is the – most commonly used. Other examples are perfluorocarbon

liquids, semifluorinated alkanes, Heavy Silicone Oil (HSO).

3. Polymers like – hydrogels, smart hydrogels, and thermosetting hydrogels.


1. GASES

I. Air



3


Air was the first gas injected into the eye. First used by Ohm in 1911 to repair retinal detachment. Composed of different gases (mainly N 2 , O 2 , CO 2 , and others at lower concentrations), it is-

Colorless and inert

Inexpensive and easily available

Non expansive

Low refractive index (approximately 1.00 nanometers), which causes complete light reflection and therefore poor optical function i.e. fundus evaluation problematic until gas reabsorption.

Easily diffuses in the blood circulation, reducing its tamponade effects in a few (3) days.

Its tamponade effect depends on the dimension and the position of the intraocular bubble, consequent to the position of the patient’s head.

Its use is limited to pneumatic retinopexy at the end of vitrectomy surgery and as an emergency option.

ii. Sulfur hexafluoride (SF 6 ) and Perfluoropropane (C 3 F 8 )


Both are heavier than air, colorless, odourless, nontoxic and expansile.

Two main characteristics of gases which help in reattaching the retina are

High Surface tension – which occludes the break

Buoyancy – which provides a force that pushes the retina back

SF 6 expands to about the double of the volume injected within 24 to 48 hours and exerts an effect for 1 to 2 weeks whereas C 3 F 8 expands to about four times its original volume within 72 to 96 hours and persists for 6 to 8 weeks.

Hence, commercially available at a definite non expansive concentration (SF 6 20% and C 3 F 8 14%) in order to avoid errors during presurgical dilution.

Used as a non expansile mixture with air after pars plana vitrectomy (PPV) while during pneumoretinopexy used in 100% concentration as expansile gas.

In surgeries performed under general anesthesia, dinitrogen monoxide (N 2 O) is strictly forbidden as anesthetic and analgesic due to its strong diffusion tendency. In such a case the rapid vascular/eye exchange of these gases leads to a rapid expansion of the intraocular bubble resulting in severe intraocular pressure rise.

Patients with intraocular gases are advised against air or high altitude travel for about 2 weeks and 6 weeks following the administration of SF 6 and C 3 F 8 respectively, since the reduction of atmospheric pressure will lead to expansion of intraocular gas bubble and cause considerable increase of intraocular pressure.

At the same time they should avoid diving: the hyperbaric pressure occurring during scuba diving causes hypotony and partial globe collapse.



Indications


Giant retinal tears

Retinal detachment complicated by proliferative vitreoretinopathy

Traumatic RD

One eyed patient with need of early visual rehabilitation

Complications


Tamponade of the inferior retina is difficult due to its low specific gravity.

Emulsification – breakdown on silicone oil most common complication.

Increased IOP due to-

(I) Immediate postoperative rise due to inflammation


(II) Pupillary block glaucoma – can be prevented by inferior iridectomy.


(III) Chronic glaucoma – when emulsified oil gets trapped in trabecular meshwork


4. Cataract


5. Band shaped keratopathy


6. Redetachment of retina after silicon oil removal


7. Macular edema



Disadvantages

• Needs repeat surgery for removal

• Postoperative change in refraction –

(I) Hyperopia in phakics and pseudophakics

(II)Myopia in aphakics





ii. Heavy silicone oil (HSO)


Heavy silicone oil is a tamponade agent formed from a mixture of SO and partially fluorinated octane (PFA) that is heavier than water.

Like silicone oils, they have good transparency, higher density than water, and higher viscosity.

Chemically inert and tendency of emulsification is less than that of silicone oils.

Four molecules have been identified: Oxane HD, Densiron 68 and 68 LV, and HWS 46-3000.

Used for complex retinal detachment involving the inferior part of the retina complicated by proliferative vitreoretinopathy.

Its removal requires strong active aspiration due to its high viscosity. The heavy SO may remain strictly adherent to the retina surface (“sticky oil phenomenon”) causing inflammation and tissue reactivity.

Complications include cataract, anterior segment inflammation, emulsification and elevated IOP.

iii. Perfluorocarbon Liquids (PFCls)


A fluorochemical in which all the hydrogen atoms are replaced by fluorine.

  *clear, colorless, and odorless

   *higher specific gravity than water

  *low viscosity favors easy introduction and removal

  *refractive index similar to that of water

  *hydrophobic and lipophobic and so immiscible but they could form emulsions

Initially used in medicine when it was discovered to carry oxygen atoms in the same manner as the blood.

In 1987, Chang et al. used PFCL for the first time in retinal detachment with severe proliferative vitreoretinopathy.

During vitrectomy, PFCL flattens the detached retina and displaces the subretinal fluid.

Three molecules are nowadays in use:

  *perfluorodecalin (PFD),

  *perfluoro-n-octane (PFO)

  *Perfluoro-tetradecahydrophenantrene

Used as temporary tamponades to unfold and stabilize the retina during surgical manipulation. They have to be removed at the end of the surgical procedure due to its long-term toxicity.

Complications, if left into the eye after surgery include retinal toxicity and intraocular inflammatory reactions, inducing the formation of epiretinal membranes and intraretinal layer disruption, dispersion into multiple bubbles and residual droplets have been often observed a long time after its removal.





PATIENT PERSPECTIVE


The intraocular vitreous body is a highly complex macromolecular structure, and despite significant progress over the past few decades, the ideal, universal vitreous substitute does not exist. Vitreoretinal disorders constitute a significant portion of treatable ocular disease. Advances in vitreoretinal surgery have included the development and characterization of suitable substitutes for the vitreous. Air, perfluorocarbons, expansile gases, and silicone oil serve integral roles in modern vitreoretinal surgery. These materials are used as intraoperative instruments to re-establish intraocular volume, assist in separating membranes adherent to the retina, manipulate retinal detachments and mechanically flatten detached retina. The final decision regarding the type of tamponading agent to be used in a particular vitreoretinal surgery is solely made by the operating surgeon taking into account the wide variation in their properties, clinical functions, advantages and complications.



Authors:

Dr Dhaivat Shah (MBBS, MS, DNB, FMRF) Vitreoretinal Surgeon

Dr Shirali Gokharu (MBBS) DNB Aspirant

You can contact for any related queries at: dhaivatkshah@gmail.com

The authors have no financial interests in any of the mentioned products.