Year : 1996 | Volume
: 44 | Issue : 3 | Page : 131--143
Pneumatic retinopexy: principles and practice
George F Hilton1, Taraprasad Das2, Ajit B Majji2, Subhadra Jalali2,
1 University of California San Francisco, USA
2 L.V. Prasad Eye Institute, Hyderabad, India
George F Hilton
University of California San Francisco
Pneumatic retinopexy (PR) is an alternative to scleral buckling for the surgical repair of selected retinal detachments. A gas bubble is injected into the vitreous cavity, and the patient is positioned so that the bubble closes the retinal break (s), allowing absorption of the subretinal fluid. Cryotherapy or laser photocoagulation is applied around the retinal break(s) to form a permanent seal. The procedure can be done in an outpatient setting, and no incisions are required. A multicenter randomized controlled clinical trial has demonstrated that the anatomic success rate is comparable to scleral buckling, but the morbidity is significantly less with PR. If the macula was detached for less than two weeks, the visual results are significantly better with PR than with scleral buckling. Cataract surgery was required significantly more often following scleral buckling than following PR. Two independent reports have shown that an attempt with PR does not disadvantage the eye; such that the results of scleral buckling after failed PR are not significantly different than primary scleral buckling. A comprehensive review of the world literature on PR revealed 27 statistical series totaling 1,274 eyes. These combined series had a single-operation success rate of 80%, and 98% were cured with reoperations. Pneumatic retinopexy should be considered in cases without inferior or extensive retinal breaks and without significant proliferative vitreoretinopathy. The cost of buckling varies from 4 to 10 times that of PR.
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Hilton GF, Das T, Majji AB, Jalali S. Pneumatic retinopexy: principles and practice.Indian J Ophthalmol 1996;44:131-143
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Hilton GF, Das T, Majji AB, Jalali S. Pneumatic retinopexy: principles and practice. Indian J Ophthalmol [serial online] 1996 [cited 2022 Aug 8 ];44:131-143
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The first intravitreal air injection for retinal detachment repair was performed by Ohm in 1911. At that time it was not known that retinal breaks caused detachment. Postoperative positioning to occlude the breaks was not used. Moreover the injection was made through the retina, creating an additional break. One of two cases was fortuitously reattached.
In 1938, Rosengren achieved retinal reattachment in 77% of 256 eyes with a procedure involving diathermy, drainage of subretinal fluid, intravitreal air injection, postoperative positioning, and hospitilization for several weeks and others advocated the use of intravitreal air as part of scleral buckling procedures.
Sulfur hexafluoride (SF6), shown to be nontoxic in other medical use, was injected into rabbit eyes with no demonstrated toxicity. In 1973, Norton reported favorable results with SF6 injection in conjunction with buckling and vitrectomy in the management of various types of complicated detachments. Vygantas and associates first described the intraocular injection of perfluorocarbon gas that same year Fineberg et al reported on the characteristics of SF6 while Lincoff and associates studied the perfluorocarbon gases.
Escoffery et al demostrated that the retina can be reattached with vitrectomy and fluid/gas exchange without scleral buckling. The ability of Lincoff's temporary orbital balloon to achieve permanent retinal reattachment again proved that permanent scleral buckling is not usually necessary.
Hilton and Grizzard started pneumatic retinopexy in 1984, and presented their first 20 cases a year later introducing the term "pneumatic retinopexy" (PR). PR required no conjunctival incision and no scleral buckling, vitrectomy, or drainage of subretinal fluid. In this series of 20 consecutive eyes, 90% of the detachments were cured with one operation and 100% with reoperations. In 1987, Hilton, Kelly, Salzano et al reported on 100 consecutive cases in a collaborative series, with an 84% single operation cure rate with PR alone and 98% with reoperations. These results compared favorably with a matched series of cases treated with scleral buckling.
The results of a multicenter randomized controlled clinical trial comparing PR with scleral buckling were reported in 1989. Success rates and complication rates were similar, but PR had significantly less morbidity and better visual acuity for cases where the macula had been detached for less than two weeks. Since the introduction of PR, over 150 papers have been published on PR including statistical reports on 1,274 cases. The single-operation success rate in these combined series is 80% and 98% were reattached with reoperations.
PR has become widely accepted as the treatment of choice for selected retinal detachments, as 87% of vitreoretinal surgeons perform this procedure.
II. Intraocular Gases:
Choice of gases: Sulfur hexafluoride (SF6 ) is the gas most frequently used for PR, followed by perfluoropropane (C3F8 ). Other perfluorocarbon gases such as C2F6 are in current use and success has also been reported with sterile air.
The intraocular use of sulfur hexafluoride and the perfluorocarbon gases is almost universal among vitreoretinal surgeons, and its acceptance as the standard of care has been well documented[15, 16] and, the Food and Drug Administration (FDA) has given approval for the medical use of certain SF6 and C3F8 products in 1993 for pneumatic retinopexy.
In selecting a gas, it is important to understand the longevity and expansion characteristics of the gases. SF6 doubles in volume within the eye, reaching its maximum size at about 36 hours. It will generally disappear within 10 to 14 days, depending on the amount injected. C3F8 quadruples in volume, reaching maximum size in about three days. The bubble will last 30 to 45 days in the eye. Room air does not expand but immediately starts to be absorbed. The air bubble will be gone within just a few days [Table:1]. The choice of type and amount of gas depends on two factors:
1. What size gas bubble is needed? One must usually plan for a gas bubble large enough to cover all detached breaks, simultaneously or alternately, and keep them covered for three to five days, with some extra volume as a margin of safety. The computerized tomography done by studies of Hilton and Grizzard on eyes with intraviteral gas bubbles differs substantially from that of Parer and Lincoff in model eyes. In the human eye, a 0.3 ml gas bubble covers almost 60 degrees of arc of the retina, but it takes approximately a 1.2ml bubble to cover 80-90 degrees. A very large eyeball (myopic) will require a larger volume of gas than an emmetropia eye to cover the same arc of the retina. Usually, 0.3 to 0.5 ml of gas is injected into the eye. If it is desired to inject more than 0.5 ml into the eye, multiple injections are usually planned, allowing return of intraocular pressure toward normal between injections. Alternatively, paracentesis of the anterior chamber may be performed prior to injecting a larger volume of gas, which may be followed by a second paracentesis five to ten minutes after the gas injection.
2. What length of time the bubble should stay in the eye? We feel that it is optimal for the gas bubble to cover the break(s) for four to five days and then disappear as soon as possible. A lingering gas bubble may induce tears, since movement of the head causes forcible movements of the vitreous when a gas bubble is in the eye. In most cases, the prolonged longevity of a C3F8 bubble is a disadvantage, although it may also eliminate the need to reinject gas if a new break develops. Because of its greater expansion, C3F8 allows the injection of a smaller amount of gas initially, thereby eliminating the need for paracentesis. The longevity of air is probably sufficient for most cases. Air forfeits the advantage of post-injection expansion within the eye. Our gas of choice in most cases is SF6. We use C3F8 for the occasional case which requires an exceptionally large and long-acting gas bubble to tamponade large or wide-spread breaks. Most of the time we inject 0.5ml of 100% SF6.
Characteristics of gases: Two characteristics account for their efficacy in reattaching the retina.
1. Surface tension allows the gas bubble to occlude a retinal break instead of passing into the subretinal space. The surface tension of any gas is much higher than that of other substances in the eye. Once the break is occluded, the retinal pigment epithelial pump can absorb the subretinal fluid.
2. Buoyancy provides the force which pushes the uppermost retina back against the wall of the eye. Apposition of the retina against the retinal pigment epithelium is necessary in order that chorioretinal adhesion can occur.
The initial expansion of all expandable gases is due to the law of partial pressures and the solubility coefficients of the gases involved. A 100% SF6 bubble injected into the eye contains no nitrogen or oxygen, but these gases (and very small concentrations of other gases) are dissolved in the fluid around the bubble. Due to the law of partial pressures these gases will diffuse into the SF6 bubble. SF6 also starts to diffuse out of the gas bubble into the surrounding fluid which contains no SF6. However, the body fluid gases diffuse across the gas-fluid interface much more quickly than SF6 because of the relative insolubility of SF6. The net result is an initial influx of gas molecules into the bubble, expanding its size until partial pressures equilibrate to the point where net influx equals net egress, and maximum expansion is reached. Then the bubble is gradually absorbed as the SF6 is slowly dissolved in the surrounding fluid. The diameter of the bubble shrinks at an approximately constant rate until the gas is gone. C3F8 expands more and is absorbed more slowly because it is even less soluble than SF6.
III. Preoperative Evaluation
Good preoperative evaluation is vital to the success of PR. PR is not a good procedure for surgeons with limited retinal examination skills, for three reasons:
1. Scleral buckling with encirclement may achieve retinal reattachment even if a retinal break is missed. It can be a very "forgiving" procedure in this sense. With PR, it seems that any missed retinal break can open into a detachment. The presence of a gas bubble within the vitreous cavity causes shifting of the subretinal fluid or vitreous which can open previously attached breaks.
2. When scleral buckling is done, the surgeon gets a second look in the operating room with the patient sedated, with full control of the globe, and with open conjunctiva for deep scleral depression. With PR this is not available.
3. Scleral buckling especially encirclement, supports the peripheral retina, reducing the traction which the vitreous will be able to exert on the retina in the future. Lacking this with PR, careful follow-up examinations are required to find any retinal breaks which may develop postoperatively.
In addition to a thorough examination of the retina, the preoperative evaluation for possible PR should include assessment of the following:
1. Is the patient mentally capable of following positioning directions?
2. Is the patient physically capable of maintaining positioning as needed, especially with regard to neck and back problems?
3. Will it be feasible from the standpoint of the patient's home situation for the patient to maintain the appropriate position postoperatively?
4. Will he be able to return to the surgeon's office for frequent follow-up as required?
5. Does the patient have plans to travel by air in the near future? This will pose a hazard because the intraocular gas bubble will expand at high altitudes and markedly increase the intraocular pressure.
6. Does the patient have evidence of severe glaucoma?
7. Has the patient had recent surgery on this eye which would require care to avoid causing dehiscence of the healing incision?
8. Does the presence of a filtering bleb or a corneal transplant require special handling?
9. Would the induction of increased myopia, that generally occurs following an encircling buckle, be an advantage or disadvantage given the patient's refractive status?
Because postoperative patient cooperation is essential, the nature of the procedure and his cooperation should be discussed thoroughly.
In the multicenter clinical trial which compared PR with scleral buckling,13 cases with the following characteristics were excluded:
1. Breaks larger than one clock hour or multiple breaks extending over more than one clock hour of the retina.
2. Breaks in the inferior four clock hours of the retina.
3. Presence of proliferative vitreoretinopathy grade C or D (The Retina Society Terminology Committee 1983).20
4. Cloudy media precluding full assessment of the retina.
5. Physical disability or mental incompetence precluding maintenance of the required positioning.
6. Severe or uncontrolled glaucoma.
Subsequent experience has demonstrated that selected cases that do not strictly meet these criteria can be successfully treated with PR.
Extent of breaks : Clearly breaks spanning more than one clock hour can be treated with PR. Single or multiple tears or dialyses spanning three clock hours pose no particular problem. Detached tears, six clock hours apart, are difficult to repair with PR, although alternating positioning has been used successfully. Even detachments with giant retinal tears have been cured with PR. The size of the gas bubble should generally reflect the size of the problem, although it is not always necessary to cover all breaks simultaneously with a single bubble.
While deciding whether a case is amenable to PR, it is important to recognize the differnce between attached and detached breaks. In cases where an attached break is present on the opposite side of the eye from the detached breaks, alternate positioning would not be needed. The attached break should probably be treated with laser prior to the gas injection. Care should then be taken, such as by using the "road roller" technique (described below) if necessary to prevent the bubble from pushing the subretinal fluid into the attached break and causing it to detach. Multiple flat breaks may be ignored in positioning and in the calculation of bubble size.
Inferior breaks: Most cases with breaks in the inferior four clock hours of the eye have been difficult to treat with PR, despite various attempts. Even for limber patients, it is very difficult to tilt the head below the horizontal for very long. In our opinion, a detached break in the inferior four clock hours represents a contraindication to PR. The difference between attached and detached breaks should again be recognized. Attached inferior breaks do not necessarily contraindicate PR if treated with laser and "road rolling" as mentioned above.
Proliferative vitreoretinopathy (PVR): Since PR does not relieve traction like scleral buckling or vitrectomy does, significant preoperative traction on a retinal tear is a relative contraindication to the pneumatic procedure. When a tear is adjacent to a star fold, PR is not the procedure of choice. Mild PVR which is distant from any retinal breaks generally does not contraindicate PR. More severe PVR requires scleral buckling or vitrectomy.
Cloudy media : It is important to the success of PR that all retinal breaks be identified and treated. Opacities, such as clouding of the posterior capsule, represent relative contraindications to PR. Since PR does not jeopardize an eye for future scleral buckling if needed, it may not be unreasonable to use the pneumatic procedure even when opacities obscure part of the attached retina, but this represents a calculated risk.
Inability to maintain positioning: Failure to faithfully maintain the appropriate position is an important cause of failure of PR. It is important to inquire regarding back or neck problems and to assess mental competence before deciding on PR. It should be recognized that some positions are quite easy to maintain while other require excellent cooperation. Positioning is easiest with tears between the 11:00 and 1:00 clock hours.
Glaucoma: Glaucoma has proven to be relatively unimportant as a contraindication to PR. The large majority of glaucoma patients can be treated with PR without problem. Patients with quite severe glaucoma, such as with splitting of the macular field, might suffer noticeable damage even from brief elevations in intraocular pressure, and PR might be contraindicated. Except in cases of severely impaired trabecular outflow facility, serial measurements of intraocular pressure following gas injection are not necessary.
Two other conditions warrant comment as potential relative contraindications.
Lattice degeneration: In several series, patients with extensive lattice degeneration tended to do rather poorly with PR. It does not appear that mild to moderate lattice should be considered a contraindication.
Aphakia/Pseudophakia : In some series, eyes that have had cataract surgery did poorly with PR, but in other reports this was not the case. Aphakic/pseudophakic eyes, prone to multiple tiny far-peripheral breaks, require an especially careful preoperative examination. With peripheral capsular opacities frequently present, the view of the peripheral retina can be quite limited. Such cases should probably not be done with PR. In our opinion, if the peripheral retina can be adequately examined, aphakia or pseudophakia is not a contraindication to PR. Experience has shown that eyes with an open posterior capsule tend to develop post operative breaks more frequently than eyes with the capsule intact. Like severe lattice degeneration, aphakia/pseudophakia with an open posterior capsule warrants extra caution.
PR has particular advantages in the management of certain types of retinal detachment.
1. Macular holes and other posterior retinal breaks: Retinal detachments secondary to posterior retinal breaks are difficult to treat with scleral buckling. PR is the procedure of choice in many of these cases, including retinoschisis with very posterior outer layer breaks and retinal detachments.
2. Redetachment following scleral buckling: When subretinal fluid accumulates due to an open superior break following scleral buckling, PR may be much easier than revising the buckle.
3. Filtering blebs: If a functioning filtering bleb is present, or if an eye may need a filtering procedure in the future, PR should be considered.
4. Isolated tears under the superior rectus: Placing a segmental buckle under a vertically acting muscle runs the risk of iatrogenic vertical diplopia, eliminated with PR.
5. Contraindications to general anaesthesia: Since many scleral buckling is done under a general anaesthetic, medical contraindication to general anaesthesia may indicate PR.
6. Optic pit with macular detachment: Pneumatic retinopexy is an effective option in the treatment of optic pits with macular detachment
7. Extensively scarred conjunctiva
8. Very thin sclera
9. Need to retain emmetropia or prevent anisometropia
10. Cosmetic concerns regarding post-buckling ptosis, enophthalmos, or strabismus
11. Operating room not available
12. Limited financial resources
V. Operative Technique
The technique detailed here is essentially the same as that originally described by Hilton and Grizzard, with a few modifications. The operation is usualy done in an outpatient department or in the surgeon's office. But it has been done on the ward or in the intensive care unit. When starting up the learning curve some surgeons have been more comfortable in doing the first few cases in the operating room.
Anaesthesia : PR can be done with topical, subconjunctival, or retrobulbar anaesthesia, depending on the patient's pain threshold and the surgeon's preference. Most patients do better with a retrobulbar injection. Very rarely a patient may require general anaesthesia. An injection into the anterior muscle cone will usually produce anaesthesia without akinesia initially- This has the advantage of allowing the patient to position his eye in accordance with the surgeon's instructions to cooperate in positioning his eye to facilitate crappies. After the retrobulbar anaesthetic is given, cryopexy is administered promptly before the eye becomes akinetic.
Cryotherapy versus laser photocoagulation : PR is generally done is one session with cryopexy applied to the retinal breaks prior to gas injection [Figure:1], [Figure:2]. An alternative technique involves a two-part procedure, utilizing laser instead of cryo. The first part of the procedure consists of injection of a gas bubble into the vitreous cavity. The patient maintains appropriate head positioning at home, for usually one but occasionally two days, with follow-up in the surgeon's office. Once the break is reattached, laser treatment is applied.
Photocoagulation is greatly facilitated by use of the laser indirect ophthalmoscope (LIO) which makes it easy to position the patient's head to move the gas bubble away from the break(s). Treatment can usually be applied with a slit lamp laser delivery system by tilting the patient's head as needed, thereby moving the bubble away from the break(s). Alternatively, one can treat the breaks through the gas bubble if the bubble is moderately large. When treating through gas, one must be careful not to over-treat. Gas has an insulating effect, conducting heat away from the laser spot at a slower rate than liquid vitreous, which may result in excessive thermal burns with retinal necrosig and hole formation.
It is generally best not to attempt to apply laser until the retina is completely reattached at the break site. However, laser can sometimes be applied even if the retina is not yet entirely attached by treating through the gas bubble, or by using scleral depression to flatten the retina. It is cautioned not to over treat.
The chorioretinal adhesion with laser may be quicker and firmer than that with cryo. On the other hand, the one-part procedure with cryo is usually more convenient, and the breaks may be easier to find and treat when they are open.
Certain circumstances might indicate the use of laser instead of cryo. Very posterior breaks are easier to treat with laser. If multiple and /or large breaks are present, the risks of extensive cryopexy might warrant the use of laser instead, or cryopexy might be applied after the retina has been reattached. When there has been a recent incision in the eye, laser may be safer than cryo.
Preparation of the eye: Following the anaesthesia and cryopexy, the next step is to massage the eye to reduce intraocular volume, making room for the gas bubble. Retropulsion of the eye into the orbit dehydrates the orbital fat but is less effective at reducing the intra ocular volume. Instead, a scleral depressor is placed against the temporal equator and the eye is pressed firmly against the nasal orbital wall. Firm pressure is applied for 45 seconds, then relaxed for 15 seconds to allow perfusion of the retinal vasculature. This cycle is repeated until the intraocular pressure is less than 5 mm Hg. This manoeuver causes egress of fluid from the eye, and also stretches the scleral fibres allowing for more intraocular volume. Examination and cryopexy with firm scleral depression will have started this process, but usually additional massage is needed. Preoperative medications for reducing the intraocular pressure can be used but save little massaging time, so we have discontinued such medications. Alternatively, a pre -injection paracentesis can be performed. Many surgeons spend little time with massage, planning instead to do a paracentesis either just before or after the gas injection. A sterile lid speculum is utilized. Eight to ten drops of undiluted BetadineR solution are instilled directly onto the cornea and conjunctiva. After three minutes the injection site is dried with a sterile cotton tipped applicator and the eye is ready for injection of gas.
Preoperative topical antibiotics add nothing to the sterility of a careful antiseptic preparation. Meticulous sterility is mandatory. No cases of endophthalmitis have been reported following pneumatic retinopexy when BetadineK solution was used as described above.
Preparation of the gas: A pressure reducing system is attached to the gas cylinder to allow drawing the gas from a low pressure system. High pressure can blow out the millipore filter and render it useless in sterilizing the gas. A condom catheter can be attached to the cylinder, or a step down valve system can be used. Alternatively the gas may be drawn into a large syringe and then transferred to a small syringe.
The selected gas is drawn through a millipore filter into a 3 ml syringe in sterile fashion. The tube connecting the gas cylinder with the syringe including the filter, is flushed through with gas to insure no dilution with room air. The first withdrawal of the gas is discarded and approximately 1ml of gas is withdrawn. A disposable 30 gauge one-half inch (12mm) needle is then placed tightly on the syringe and excess gas is expelled to leave the exact amount intended for injection. The gas should not be stored in the syringe for more than a few minutes prior to injection because of the high risk of gas leakage.
Injection of gas: An injection site is selected 4mm posterior to the limbus. The selected site is ideally away from large open retinal breaks, highly detached retina, or detached pars plana epithelium. The head of the supine patient is turned 45 degrees to one side to make the injection site uppermost. The needle is then passed into the eye perpendicular to the sclera. The needle is pushed 6 to 8 mm into the eye to ensure that the tip is well into the vitreous, directing the tip away from areas of highly bullous detachment. Then it is withdrawn until 3 mm of the needle remains in the eye [Figure:3],[Figure:4]. This will ensure that the tip remains in the vitreous but is shallow enough to prevent multiple small bubbles ("fish eggs").
We do not recommend trying to visualize the needle tip with an indirect ophthalmoscope. The manoeuvering required to do so may cause the needle tip to damage intraocular structures, and we doubt that the appropriate depth can be more accurately gauged than by external measurement.
With the needle in the correct position, a moderately brisk injection of the entire volume of gas is performed [Figure:5]. This facilitates formation of a single bubble at the needle tip. The injection should not be so brisk as to force bubbles of gas deep into the vitreous before their buoyancy can make them rise. It requires to inject smoothly and quickly but not with excessive force and one should hold the plunger down until the needle is withdrawn to prevent escape of gas back into the syringe.
Because some gas may escape instantly upon removal of the needle, a cotton-tipped applicator should be used to occlude the perforation site. The applicator must be pressed against the shaft of the needle and rolled immediately over the hole as the needle is withdrawn. The head is then rotated 90 degrees to move the gas away from the injection site and the applicator is removed. Escape of gas into the subconjunctival space is not harmful but may not leave enough gas in the vitreous cavity.
As an alternative to occluding the needle hole with a cotton-tipped applicator the patient's head may be rotated 90 degrees to the opposite side before withdrawing the needle. This allows the bubble to float away from the injection site and prevents gas from escaping through the needle tract. This manoeuver should be rehearsed with the patient prior to inserting the needle to ensure smooth coordination. With only 3 mm of needle in the eye, this manoeuver is unlikely to injure the lens. When the needle is then withdrawn, liquid vitreous will sometimes escape through the needle tract into the subconjunctival space. This is a fortuitous development which will probably eliminate the need for paracentesis. Vitreous incarceration in the pars plana injection site probably occurs but is not known to cause clinically significant complications.
Following injection the eye is examined with the binocular indirect ophthalmoscope to make the following three determinations:
1. Is the central retinal artery occluded? Occlusion of the central retinal artery can be safely observed for ten minutes. During this time the intraocular pressure declines and the artery may reopen, but if it does not, paracentesis should be performed (see "Special Procedures"). Many surgeons routinely perform a prompt paracentesis following injection of the gas, especially when more than 0.4 ml was injected.
2. Is a single gas bubble present or are there multiple small bubbles ("fish eggs")? Fish eggs are undesirable because a small gas bubble can get through a retinal break into the subretinal space. (See the section on "Special Procedures" below for suggestions on management of fish eggs).
3. Is the bubble mobile within the vitreous or is it trapped at the injection site? If the bubble is beneath the pars plana epithelium or trapped in the space bordered by the pars plana, the anterior hyaloid face, and the lens (the canal of Petit), it will not move when the head is turned and will take on a semicircular shape. This has been termed the "donut sign," the "sausage sign", or the "bagel sign". Management of this occurrence is discussed below under " Special Procedures".
The "road roller" technique is now used if indicated (see "Special Procedures"). We instill steroid-antibiotic ointment and patch the eye. The meridian of the retinal break is marked as an arrow on the patch to indicate to the patient and family the head position which is to be maintained [Figure:6]. We have a hand-held mirror available to show the patient that the head should be positioned so that the arrow is pointing directly at the ceiling. The patient is allowed to go home and then seen for follow-up on the following day.
VI. Special Procedures
Paracentesis: The intended paracentesis site should be resterilized with BetadineR solution unless strict sterility has been maintained. A 30 gauge 1/2 inch needle on a one ml syringe with the plunger removed is passed obliquely into the anterior chamber through the limbus, staying over the iris with the bevel up. Fluid flows passively into the syringe. As the chamber shallows, gentle pressure on the central cornea with a cottontipped applicator will'deepen the peripheral angle and facilitate fluid egress [Figure:7]. Usually no more than 0.2 ml need be removed.
If the posterior lens capsule is absent or open, paracentesis should not be performed through the limbus to avoid incarceration of vitreous in the limbal needle tract. A 30 gauge bent needle is passed through the pars plana, and angled into the anterior chamber, either through the pupil or through iris tissue.
The central retinal artery is reexamined to ensure its patency. As long as the central artery is open (widely patent or with strong pulsation) measurement of the intraocular pressure has little meaning. The pressure will soon return to normal and not increase even though the gas is expanding.
If there has been surgery within six weeks which weakens the globe, or if there is glaucomatous optic nerve damage, it is recommended to perform paracentesis before gas injection. This will prevent dehiscence of the wound or pressure damage to the optic nerve. Crappies will also stress the unhealed wound; therefore laser is recommended. Some surgeons perform paracentesis prior to gas injection in all cases.
Multiple small gas bubbles ("Fish Eggs") Fish eggs are usually due to faulty injection technique. In probable order of importance the following steps will usually prevent this occurrence:
1. Make sure that the needle is shallowly within the vitreous at the time of injection.
2. Make sure that the injections site is uppermost.
3. Injection with the needle vertical; direct perpendicular to the floor and toward the center of the eyeball.
4. Inject briskly but not too brisk.
If fish eggs do occur some authors recommend inducing them to coalece by flickling the eye with a cotton-tipped applicator or finger. Turn the eye so that pars plana, without underlying retinal breaks, is uppermost and flick this site moderately firmly. Other authors prefer to have the patient stay strictly positioned to keep the bubbles away from retinal breaks for 24 hours. If all retinal breaks are tiny this may not be necessary, but keep in mind that breaks can stretch a little. The multiple bubbles will usually coalesce into one larger bubble spontaneously within 24 hours, and then the patient can adopt a position with the retinal break(s) uppermost.
Gas entrapment at the injection site: Following gas injection, if the gas bubble remains trapped at the injection site, it is probably trapped in the canal of Petit. If the trapped bubble is small, no treatment is necessary. Unless there is an immediate threat of the macula detaching, the problem can usually be solved by facedown positioning for 24 hours. This will encourage the trapped anterior gas bubbles to pass through the vitreous gel by its own buoyancy, aided by the gas expansion.
If necessary a large trapped bubble can be removed by passing a 25 or 27 gauge needle back through the injection site. This needle is mounted on a syringe with a small amount of sterile saline, with the plunger removed. The injection site is positioned uppermost and the needle is passed vertically into the bubble. Sometimes it takes a little manipulating to break the surface tension of the bubble and get it to escape. Most of the gas will escape, bubbling up through the fluid in the syringe. At another site, reinject the gas deeper into the vitreous, with 5 to 6 mm of the needle in the globe.
"Road roller": If bullous subretinal fluid extends almost to the macula, placement of a bubble against the detachment may cause macular detachment. This complication can be avoided by the "road roller" technique. Following injection of the gas bubble the patient's head is turned to a face-down position in such a way as to cause the bubble to traverse a meridian without any retinal breaks en route to the macula. Over ten to fifteen minutes, the patient's face position is very gradually changed until the retinal break is uppermost, causing the bubble to roll toward the retinal break, pushing the subretinal fluid back into the vitreous and flattening the retina [Figure:8].
Subretinal fluid will be expressed through the retinal break into the vitreous cavity at a rate depending on the size of the break. Since crappies causes liberation of pigment epithelial cells, which may cause proliferative vitreoretinopathy if they get in the vitreous cavity, crappies should be deferred until after the "road rolling" manoeuver.
Whether "road rolling" is necessary to prevent macular detachment depends on several factors:
1. How close the detachment is to the macula: only detachments well within the arcades usually need "road rolling".
2. How bullous is the detachment.
3. How large is the gas bubble.
Possible indications for "road rolling" include prevention of iatrogenic macular detachment, prevention of iatrogenic detachment of an attached retinal break, reduction of a bullous detachment overhanging the optic nerve (preventing visualization of the central retinal artery during the procedure), reduction of subretinal fluid to encourage more rapid resolution of retinal detachment. This might also be of use in cases where all retinal breaks cannot be covered at one time by the gas bubble. Also, where large retinal breaks are present, this may minimize the chance of subretinal gas.
VII. Post Operative Management
Analgesics such as Ibuprofen (Brufen) is usually sufficient for postoperative pain control. We recommend considerable restriction in activity initially, liberalizing day by day as the retina reattaches, the chorioretinal scar matures, and finally the gas bubble absorbs. The patient is allowed to return to work two weeks after the procedure. The patient should be advised not to travel by air until the bubble is gone or is quite small.
If all retinal breaks are closed, the subretinal fluid is usually absorbed within 24 to 48 hours [Figure:9],[Figure:10]. If the fluid is not absorbing, a new or missed break exists, the bubble is too small, or the patient has not been positioning properly.
Ensuring proper patient positioning requires considerable effort. It is helpful to explain to the patient why positioning is important and to demonstrate the position which allows the bubble to close the breaks. The neck strain or an oblique head position can be eased by explaining that the patient can alternate positions, because sitting with the head tilted 45 degrees to the left is the same as lying on a couch with the head tilted 45 degrees to the right.
Patient positioning is maintained during waking hours (at least 16 hours) for five days; however, three days are probably adequate. The patient should not sleep face-up to avoid gas-induced cataract formation in the phakic eye, or ciliary-block glaucoma in the aphakic eye. The patient should be seen on the first postoperative day. Depending on resolution of subretinal fluid, the next follow-up is scheduled on the third day, fifth day and subsequently at one week, two weeks, one, two, and four months later. The main purpose of this frequent schedule is to look for new retinal breaks. These breaks do not jeopardize the final outcome if close follow-up results in early detection and treatment.13,32 At least half of these postoperative breaks can be cured with an office procedure without resorting to scleral buckling.
Inferior subretinal fluid or loculated pockets of subretinal fluid sometimes persist for weeks or months. As long as the fluid is not increasing and the macula is attached, reoperation is not necessary.
Subretinal gas: Subretinal gas in the absence of "fish eggs" at the time of injection is very rare. If "fish eggs"are noted following injection, one should examine carefully for the presence of subretinal gas. Once the gas bubble expands it may be more difficult to get it back out of the break it passed through [Figure:11], [Figure:12]. In none of the cases in McDonald's series was the subretinal gas noted immediately after injection because they all had "fish eggs". If a gas bubble does get beneath the retina, it gives the detached retina a pearly, domeshaped retractile sheen.
An attempt is first made to massage the bubble back toward the retinal break by scleral depression assisted by positioning as needed. If this fails and the amount of subretinal gas is large, prompt surgical removal is probably required.
Smaller subretinal bubbles can be ignored with injection of a larger bubble into the vitreous. In spite of the subretinal bubble, the break can usually be secluded from liquid vitreous with strict positioning, and subretinal fluid and gas will be absorbed. The smaller subretinal bubble will disappear before the larger vitreous bubble and the detachment can be repaired, injecting additional gas if needed.
Iatrogenic macular detachment: This preventable complication is avoided by using the "road roller" technique as described above.
New retinal breaks: New or missed retinal breaks following PR occurred in 13% of 1,274 eyes. This is similar to the 14% incidence of new retinal breaks following crappies or laser without the injection of intravitreal gas. This very similar incidence with or without gas suggests that the gas bubble is not the cause of new /missed breaks postoperatively. These new breaks may simply be a manifestation of the progressive nature of the rhegmatogenic disease process.
In the multicenter trial, 96% of eyes with new breaks were successfully reattached. Approximately half of such breaks were managed in the office or the outpatient department without scleral buckling. New breaks can often be treated with pneumatic techniques, without automatically resorting to scleral buckling.
Proliferative vitreoretinopathy (PVR): PR does not appear to increase the incidence of proliferative vitreoretinopathy. In the multicenter clinical trial, PVR occurred in 5% of eyes following scleral buckling and 3% of eyes following PR. It may be possible to reduce the incidence of PVR by replacing crappies of detached breaks with laser treatment of reattached breaks.
IX. Comparison with Scleral Buckling
In review of the worldwide literature (statistics on 1.274 cases), the single-operation success rate was 80%, and 98% were reattached with reoperations, which compares favorably with scleral buckling. A multicenter randomized controlled clinical trial with 198 patients compared PR with scleral buckling.[13,32] The key findings of this study (two year follow-up) are shown in [Table:2].
Comparison of the two procedures is summarized as follows:
1. Postoperative visual acuity is significantly better with PR than with scleral buckling for eyes where the macula was detached for less than 14 days (p = 0.05).
2. Anatomic results are not significantly different.
3. Complications are similar, based on a score system which weighted heavily the need for postoperative laser or cryo.
4. Morbidity is less with PR
5. Cataract surgery was required four times more often with scleral buckling than with PR..
6. Cost is generally much less with PR.35
7. Scleral buckling is the more versatile procedure, with some detachments not amenable to PR. At least 40% of detachments are candidates for PR. PR can treat some detachments which scleral buckling cannot, such as detachments with very posterior breaks.
8. The main disadvantage of PR is the need for postoperative positioning and very close follow-up care.
PR is more versatile than the temporary episcleral balloon, being able to treat larger breaks, more widely spread breaks, and more posterior breaks than the balloon can treat. However, the balloon can treat detached inferior breaks which the bubble cannot.
X. Economic Considerations
PR is less expensive than scleral buckling because there is no need for (1) a preoperative history and physical examination, (2) preoperative laboratory work, (3) an anaesthesiologist, (4) an assistant surgeon, (5) operating room expenses, and (6) hospitalization costs. The cost of scleral buckling, with its associated expenses, is usually four to ten times that required for pneumatic retinopexy.
Figures 1, 2, 5, 8, 9 and 10. Reproduced with permission from Hilton GF, Grizzard WS. Pneumatic retinopexy: a two-step outpatient procedure without conjunctival incision. Ophthalmology 93:626-641,1986.
Figures 3 and 4. Courtesy of W. Sanderson Grizzard, M.D.
Figures 6 and 7. Reproduced with permission from Hilton GF, Kelly NE, Salzano TC et al. Pneumatic retinopexy: a collaborative report of the first 100 cases. Ophthalmology 94:307-314,1987.
Figures 11 and 12. Reproduced with permission from Hilton GF, Tornambe PE. The Retinal Detachment Study Group. Pneumatic retinopexy: an analysis of intraoperative and postoperative complications. Retina 11:285-294,1991.
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