Intraocular gas tamponades

Outcomes of short- versus long-acting gas tamponades in vitrectomy for rhegmatogenous retinal detachment

BACKGROUND

In vitrectomy for rhegmatogenous retinal detachment, long-acting gas tamponades (LGT) such as C3F8 or C2F6 may improve surgical success rate due to their prolonged effect compared to a short-acting gas tamponade (SGT) with SF6. On the other hand, SGT allow a significantly faster visual rehabilitation after surgery and may reduce the risk of gas-related complications. As comparative data in retinal detachment surgery is limited, we assessed the outcomes of vitrectomies using either LGT or SGT.

METHODS

We retrospectively analyzed 533 eyes of 524 consecutive patients diagnosed with primary rhegmatogenous retinal detachment not complicated by proliferative vitreoretinopathy (PVR) and treated by vitrectomy at two clinical sites. Depending on the site the patients presented at, they received either preferentially LGT (study site 1) or SGT (study site 2). Retinal re-detachment rates during a period of 6 months following surgery were analyzed.

RESULTS

At study site 1, 254 of 278 eyes (91.4%) were treated by LGT (C3F8 72.3%; C2F6 19.1%), whereas at study site 2, 246 of 255 eyes (96.5%) received SGT (SF6). Rates of retinal re-detachment in the LGT- and SGT-treated groups were similar with 23 of 254 eyes (9.1%) and 24 of 246 eyes (9.8%), respectively (p = 0.9). Median time to re-detachment was 5.7 weeks in the LGT-treated group and 4.4 weeks in the SGT-treated group (p = 0.4).

CONCLUSION

In rhegmatogenous retinal detachment repair by vitrectomy, the use of SGT results in comparable rates of successful retinal re-attachment as LGT. Given the faster visual rehabilitation with SGT, these results suggest SGT as a sensible alternative to LGT in surgery of retinal detachment without PVR.

Comparison of efficacy of three gases for anterior chamber tamponade in Descemet's membrane endothelial keratoplasty

PURPOSE

To compare the efficacy of three different gases for intraocular tamponade: 100% air, 10% perfluoropropane (C3F8), and 10% sulfur hexafluoride (SF6), in Descemet's membrane endothelial keratoplasty (DMEK).

MATERIALS AND METHODS

The medical records of 138 patients who underwent DMEK were reviewed retrospectively, with the primary outcome being the rebubbling rate in the first week following surgery. Other clinical outcomes, such as best-corrected visual acuity (BCVA), central corneal thickness (CCT), incidence of rebubbling after the first week, endothelial cell density (ECD), graft detachment, graft failure, pupillary block, and intraocular pressure (IOP) changes were also analyzed.

RESULTS

Of the 138 patients, 57 were in group 1 (treated with air), 44 in group 2 (treated with 10% C3F8), and 37 in group 3 (treated with 10% SF6). Group 3 showed significantly lower rates of graft detachment and rebubbling compared to groups 1 and 2 (P<0.001). However, there was no significant difference in postoperative BCVA among the groups. At one year, the mean endothelial cell loss was 32% in group 1, 30% in group 2, and 33% in group 3 (P=0.715). One patient in group 1 experienced pupillary block and increased IOP, while there were no such occurrences in the other groups. There was no difference between the groups in terms of graft failure.

CONCLUSION

The use of 10% SF6 in DMEK surgery may be a good option due to its efficacy in preventing graft detachment, low rebubbling rate, and potential for minimizing complications.

A Comparison of Adjustable Positioning and Free Positioning After Pars Plana Vitrectomy for Rhegmatogenous Retinal Detachment: A Prospective Randomized Controlled Study

Purpose

To compare the effectiveness and safety of adjustable and free postoperative positioning after pars plana vitrectomy (PPV) for rhegmatogenous retinal detachment (RRD).

Design

Prospective, randomized controlled study.

Methods

A total of 94 eyes with RRD were enrolled from April 2020 to April 2023 and monitored postoperatively for at least 3 months. All patients underwent PPV combined with silicone oil injection or gas tamponade and were randomly divided postoperatively into two groups: an adjustable positioning group and a free positioning group. The success of the outcome was based on the retinal reattachment rate, best corrected visual acuity (BCVA), postoperative complications, and ocular biometric parameters such as anterior chamber depth (ACD) and lens thickness (LT).

Results

The initial retinal reattachment rate was 97.9% in the adjustable positioning group and 95.7% in the free positioning group, manifesting no statistical difference between the two groups. Similarly, no statistical difference was observed between the two groups in the final BCVA, which was significantly improved compared to the preoperative BCVA. The comparison of the 1-month postoperative ACD and LT with the preoperative values showed no statistically significant differences in the two groups. The rates of complications were not statistically different in the two groups.

Conclusion

After treating RRD using PPV, neither the adjustable nor the free postoperative positioning affected the retinal reattachment rate or the incidence of complications. Therefore, our study showed that it is safe and effective to adopt free positioning postoperatively, which may provide more options for patients with RRD undergoing PPV.

Vitreous Substitutes from Bench to the Operating Room in a Translational Approach: Review and Future Endeavors in Vitreoretinal Surgery

Vitreous substitutes are indispensable tools in vitreoretinal surgery. The two crucial functions of these substitutes are their ability to displace intravitreal fluid from the retinal surface and to allow the retina to adhere to the retinal pigment epithelium. Today, vitreoretinal surgeons can choose among a plethora of vitreous tamponades, and the tamponade of choice might be difficult to determine in the ever-expanding range of possibilities for a favorable outcome. The currently available vitreous substitutes have disadvantages that need to be addressed to improve the surgical outcome achievable today. Herein, the fundamental physical and chemical proprieties of all vitreous substitutes are reported, and their use and clinical applications are described alongside some surgical techniques of intra-operative manipulation. The major upcoming developments in vitreous substitutes are extensively discussed, keeping a translational perspective throughout. Conclusions on future perspectives are derived through an in-depth analysis of what is lacking today in terms of desired outcomes and biomaterials technology.

Current Situation and Challenges in Vitreous Substitutes

Vitreo-retinal disorders constitute a significant portion of treatable ocular diseases. These pathologies often require vitreo-retinal surgery and, as a consequence, the use of vitreous substitutes. Nowadays, the vitreous substitutes that are used in clinical practice are mainly divided into gases (air, SF₆ , C₂ F₆ , C₃ F₈ ) and liquids (perfluorocarbon liquids, silicone oils, and heavy silicone oils). There are specific advantages and drawbacks to each of these, which determine their clinical indications. However, developing the ideal biomaterial for vitreous substitution continues to be one of the most important challenges in ophthalmology, and a multidisciplinary approach is required. In this sense, recent research has focused on the development of biocompatible, biodegradable, and injectable hydrogels (natural, synthetic, and smart), which also act as medium and long-term internal tamponade agents. This comprehensive review aims to cover the main characteristics and indications for use of the extensive range of vitreous substitutes that are currently used in clinical practice, before going on to describe the hydrogels that have been developed recently and which have emerged as promising biomaterials for vitreous substitution.

Advances in the treatment of rhegmatogenous retinal detachment

The pathogenesis of rhegmatogenous retinal detachment depends on three factors, namely, retinal rupture, vitreous liquefaction and traction causing the retina to separate from the pigment epithelium, among which retinal rupture is the most important. Retinopathy is caused by a gap between the neurosensory retina and the retinal pigment epithelium, which severely damages the visual function of the patient. Therefore, early clinical discovery, prevention and selection of an appropriate treatment are important. This article reviews progress in the treatment of retinal detachment.

The Effect of Altitude on Intraocular Pressure in Vitrectomized Eyes with Sulfur Hexafluoride Tamponade by the Friedenwald Method: Rabbit Animal Model

The aim of this study is to assess the change in intraocular pressure after a road trip, in eyes with different levels of filling with gas tamponade. Five rabbit eyes were subject to pars plana vitrectomy and gas tamponade (filling percentage: 25%, 50%, and 100% of nonexpansile SF6, 100% saline solution, and 100% room air). A sixth eye was injected with 0.35 cc of undiluted SF6 without vitrectomy. Guided by global positioning system, they were driven to the highest point of the highway connecting Mexico City with Puebla city and back, stopping every 300 m to assess intraocular pressure. The rabbit's scleral rigidity and estimation for human eyes were done by using the Friedenwald nomogram. Maximum altitude was 3209 m (Δ949 m). There were significant differences in intraocular pressure on the rabbit eyes filled with SF6 at 100%, 50%, 25%, and 100% room air. Per every 100 m of altitude rise, the intraocular pressure increased by 1.53, 1.0046, 0.971, and 0.97 mmHg, respectively. Using the human Friedenwald rigidity coefficient, the human eye estimate for intraocular pressure change was 2.1, 1.8, 1.4, and 1.1 mmHg per every 100 m of attitude rise. Altitude changes have a significant impact on intraocular pressure. The final effect depends on the percentage of vitreous cavity fill and scleral rigidity.

Pneumatic release of focal vitreomacular traction

PurposeTo study the efficacy of a single intravitreal injection of expansile gas as a valuable alternative to current treatment options (conservative, pharmacological, and surgical) in patients with symptomatic, focal vitreomacular traction (VMT).Patients and methodsThis study comprises a retrospective, interventional case series of patients. Twenty eyes in seventeen patients with symptomatic and persisting focal VMT were treated in an outpatient setting with an intravitreal gas injection of 0.2 ml. In 19 eyes, 100% hexafluoroethane (C₂F₆) was used. One eye received sulfur hexafluoride (SF₆). To all but three patients posturing advice was given. Patients were reviewed with a full-eye examination and ocular coherence tomography (OCT) after 14 days and later. The primary outcome measure was the release of VMT on OCT.ResultsIn 17 of the 20 (85.0%) treated eyes, a release of VMT was achieved as documented on OCT. The release of VMT was diagnosed during the first month after injection in 11 eyes of 11 patients and within 3 months in 16 eyes of 15 patients. In all but five of our patients, best corrected visual acuity (BCVA) remained stable or improved. In four patients, the progression or development of cataract was the probable cause of the decrease in BCVA. One patient developed a stage II macular hole after injection and needed vitrectomy. None of the treated patients developed retinal breaks.ConclusionIntravitreal expansile gas injection could offer a minimally invasive, low-cost alternative treatment in patients with symptomatic, persisting VMT. Additional studies on a larger number of patients are required.

INTRAVITREAL SULFUR HEXAFLUORIDE INJECTION FOR THE TREATMENT OF VITREOMACULAR TRACTION SYNDROME

PURPOSE

Vitreomacular traction (VMT) syndrome can cause symptomatic metamorphopsia and decreased visual acuity. Although it is typically treated with vitrectomy or intravitreal ocriplasmin injection, these procedures can be invasive and costly. The purpose of this retrospective, consecutive case series was to evaluate the efficacy of intravitreal expansile sulfur hexafluoride gas injection for the treatment of symptomatic VMT syndrome.

METHODS

Nine eyes of 9 patients with symptomatic VMT syndrome on spectral domain optical coherence tomography received an intravitreal injection of 0.3 mL of 100% sulfur hexafluoride. The primary outcome was the number of eyes with release of VMT on spectral domain optical coherence tomography at 1 month after treatment. Secondary outcomes included change in visual acuity and central subfield thickness 1 month after treatment.

RESULTS

Five patients (55.6%) had release of VMT on spectral domain optical coherence tomography by 1 month after injection. Two patients who had Stage I macular holes before injection had closure of the macular holes. Mean visual acuity at 1 month improved slightly after injection by 0.09 logMAR units, although this change was not statistically significant (P = 0.15). Central subfield thickness on spectral domain optical coherence tomography decreased by an average of 35.3 microns after injection (P = 0.004). All eyes with release of VMT had pretreatment vitreomacular adhesion of less than 521 microns and none had epiretinal membranes. One patient (11.1%) developed a peripheral retinal hole at 1 month after injection.

CONCLUSION

Intravitreal injection of expansile sulfur hexafluoride gas is a low-cost and minimally invasive alternative for the treatment of symptomatic VMT syndrome. Further study is warranted.

Comparison of sulfur hexafluoride and air for donor attachment in Descemet stripping endothelial keratoplasty in patients with pseudophakic bullous keratopathy

PURPOSE

The aim of this study was to evaluate the clinical efficacy and safety of sulfur hexafluoride (SF6) as a tamponading agent after donor placement during Descemet stripping endothelial keratoplasty (DSEK) surgery and to compare the outcomes with those of air.

METHODS

Forty-four eyes of 44 consecutive patients who underwent DSEK were included in the study. Air was used in 22 eyes of 22 patients (air group), and SF6 was used in 22 eyes of 22 patients (SF6 group) to attach the donor lenticule. The complications, corrected visual acuity (CVA), and the endothelial cell density (ECD) results were compared between these 2 groups.

RESULTS

Six eyes had graft dislocation in the air group that underwent successful rebubbling on postoperative day 1. There was no graft dislocation in the SF6 group. There was no other complication observed in both the groups. The mean increase in the CVA was 1.09 ± 0.36 logarithm of the minimum angle of resolution in the air group, whereas it was 0.80 ± 0.57 logarithm of the minimum angle of resolution in the SF6 group. The mean increase in the CVA was not statistically different between the 2 groups (P = 0.060). Compared with the mean ECD in donor grafts, the mean decrease in the ECD was 222 ± 86 (44%) cells per square millimeter in the air group and 178 ± 52 (39%) cells per square millimeter in the SF6 group at the 1-year follow-up. The mean decrease in the ECD was statistically significantly higher in the air group compared with that in the SF6 group (P = 0.049).

CONCLUSIONS

SF6 is comparable to air for attaching the donor graft as a tamponading agent in DSEK surgery.

The toxic effect of air on primary human retinal pigment epithelium cells

PURPOSE

To investigate the toxic effect of air on primary human retinal pigment epithelium cells (RPE) over time.

METHODS

RPE cultures were retrieved from six donor eyes and cultivated at 37 °C in 5% CO(2) and 95% humidified air. The RPE were divided in six groups with each group containing four samples. Six groups of RPE cultures were set up and four samples were enclosed in each group: group 1 consisted of samples in which RPE were exposed to air for 1 hour. Group 2 consisted of RPE exposed to air for 3 hours, group 3 for 6 hours group 4 for 12 hours group 5 for 24 hours and group 6 for 36 hours respectively.

RESULTS

Six hours after exposure, the morphology of the cells was still intact. At 12 hours few cells appeared enlarged. 24 hours after exposure to air the cells started losing their typical morphology and appeared deformed. Viability was higher than 95% in groups 1-3 while for groups 4-6 was 75.5%, 15.5% and 7.3%, respectively.

CONCLUSION

The toxic effect of air for the studied in vitro model of RPE is not significant for the first 6 hours. The morphology of the cells progressively changed after 12 hours of exposure and almost all cells appeared apoptotic at 36 hours.

Inert gas transport in blood and tissues

This article establishes the basic mathematical models and the principles and assumptions used for inert gas transfer within body tissues-first, for a single compartment model and then for a multicompartment model. From these, and other more complex mathematical models, the transport of inert gases between lungs, blood, and other tissues is derived and compared to known experimental studies in both animals and humans. Some aspects of airway and lung transfer are particularly important to the uptake and elimination of inert gases, and these aspects of gas transport in tissues are briefly described. The most frequently used inert gases are those that are administered in anesthesia, and the specific issues relating to the uptake, transport, and elimination of these gases and vapors are dealt with in some detail showing how their transfer depends on various physical and chemical attributes, particularly their solubilities in blood and different tissues. Absorption characteristics of inert gases from within gas cavities or tissue bubbles are described, and the effects other inhaled gas mixtures have on the composition of these gas cavities are discussed. Very brief consideration is given to the effects of hyper- and hypobaric conditions on inert gas transport.

Intraoperative assessment of intraocular pressure in vitrectomized air-filled and fluid-filled eyes

PURPOSE

To ascertain the difference of intraocular pressure (IOP) measurement between vitrectomized air-filled and fluid-filled eyes.

METHODS

Thirty-one eyes of 31 consecutive patients who underwent conventional vitrectomy and intraocular gas tamponade were assessed. After vitrectomy, IOP of the fluid-filled eyes was measured by Tono-Pen. Thereafter, fluid-air exchange was performed, and IOP of the air-filled eyes was measured again. The IOP within each fluid- and air-filled eye was varied by selecting settings on the vitrectomy system, from 10 to 50 mmHg with 5-mmHg increments. Postoperatively, IOP was assessed by both Tono-Pen and Goldmann applanation tonometry (GAT). Linear and nonlinear regression analyses were conducted between intraoperatively measured Tono-Pen readings and actual IOPs. Bland-Altman plot was used to assess the agreements between postoperatively measured Tono-Pen readings and GAT readings.

RESULTS

The discrepancy between Tono-Pen readings and actual IOP in fluid-filled eyes was not significant, except for the profound high pressures over 45 mmHg. However, Tono-Pen readings in air-filled eyes were significantly lower than actual IOPs in all ranges, and Tono-Pen increasingly underestimates IOP at higher levels. Intraoperative Tono-Pen readings were correlated significantly with actual IOP and a quadratic equation evidenced the best fit (R(2) = 0.996). Postoperatively, difference of the measurements between Tono-Pen and GAT was not significant.

CONCLUSION

Tono-Pen and GAT significantly underestimate actual IOP in air-filled eyes. It should be considered that actual IOP would be greater than the measured IOP in gas-filled eyes, even though the IOP is measured as normal.

Computational simulation of altitude change-induced intraocular pressure alteration in patients with intravitreal gas bubbles

PURPOSE

To study the impact of altitude on the intraocular pressure (IOP) in an eye with an intravitreal gas bubble.

METHODS

A mathematical model was developed to simulate intravitreal gas bubble expansion caused by change in altitude. Mechanical deformation of the eye was simulated using a finite-element model. Intraocular pressure-driven changes in aqueous humor flow were also considered. Two cases were studied: 1) ascent from sea level to 3,000 ft followed by immediate return to sea level and 2) ascent to 3,000 ft followed by prolonged exposure to 3,000 ft. The effect of IOP-lowering medications was studied by changing the model parameters.

RESULTS

The IOP increase was directly related to the initial bubble size when ascent to 3,000 ft was simulated. When prolonged exposure to high altitude was modeled, loss of aqueous humor led to a less elevated value of IOP. In a typical simulated case, when the outflow facility was increased, the predicted IOP rise was reduced by 28%.

CONCLUSION

Theoretical modeling of an eye with an intravitreal gas bubble can help an ophthalmologist evaluate the impact of altitude-induced IOP changes. Our model suggests that IOP-lowering drugs could help manage altitude-induced IOP changes in the presence of intravitreal gas bubbles.

Recent trends in the management of rhegmatogenous retinal detachment

It has been nearly a century since Jules Gonin performed the first intervention for rhegmatogenous retinal detachment, trans-scleral cautery, achieving successful outcomes in close to 50% of his cases. With the introduction of alternative surgical approaches in the last half-century, including Charles Schepens' scleral buckle technique and Robert Machemer's pars plana vitrectomy, the surgical success rates have risen to close to 90%. Nonetheless, despite dramatic progress in the success of reattachment surgeries, reasonable disagreement exists as to which approach (or combination of approaches) is the best form of surgical intervention for patients with rhegmatogenous retinal detachments. In this review, the authors summarize the current knowledge of retinal detachment, and examine emerging results from the first large scale, prospective, randomized, controlled clinical trials addressing the efficacy of these surgical approaches for retinal detachment, with the hope of identifying the most appropriate (evidence-based) therapeutic intervention for the treatment of rhegmatogenous retinal detachment.