The concluding report of a year-long Commission conducted by The Lancet states that climate change is the most significant health hazard facing the world in the 21st century [1]. It was also thought that we are the first generation to feel the effect of climate change and the last generation who can do something about it [2].

The healthcare industry is responsible for an estimated 4.4% of global carbon emissions, which places it as the fifth-largest emitter worldwide [3]. In October 2020 the NHS became the first national health system pledging to attain ‘net zero’ emissions, a target it aims to achieve by 2040 [4]. Ophthalmologists have a role in making changes to mitigate our carbon footprint. One potential action is to consider our use of fluorinated gases (‘F-gases’) [5].

In the UK, sulphur hexafluoride (SF6) is the most commonly used gas tamponade for rhegmatogenous retinal detachment (RRD) repair, followed by hexafluoroethane (C2F6) and perfluoropropane (C3F8) [6, 7]. SF6 is a short-acting gas dissolving within 2–3 weeks after a full vitreous cavity fill; as compared to 4–5 weeks for C2F6 and 9–10 weeks for C3F8 [8]. The short tamponade duration is useful to avoid prolonged visual disability.

They are also potent greenhouse gases (GHG), SF6 in particular has a warming potential 23900 times that of carbon dioxide (CO2) over a 100-year period and an atmospheric lifetime of 3200 years [9]. In comparison, C2F6 and C3F8 are less potent GHG, with 9200 and 7000 times of CO2 respectively over 100 years. As such, there have been suggestions that surgeons could use dilute C2F6 or C3F8 instead of 20% SF6 to duplicate its characteristics with less GHG effect [10]. 8% C2F6 has been used in one UK Ophthalmology unit and is currently the tamponade choice as substitute for 20% SF6 [11]. Air has the least GHG effect and has been used in vitrectomy for RRD repair with success rate ranging from 79% to even 100% [12]. Despite this, air tamponade only accounted for less than 1% of the tamponade used for RRD repair in the UK in the British and Eire Association of Vitreoretinal Surgeons (BEAVRS) database study [6]. One study comparing gas and air tamponade suggested that gas tamponade is superior to air in inferior pathology [13]. However at least one RCT and a systematic review have shown no difference, although there is a lack of high-quality data [14,15,16].

Tamponades are thought to promote retinal reattachment by closing retinal breaks related to their buoyancy and surface tension. Permanent closure occurs after chorioretinal scar formation in 5–10 days following surgery, faster with intraoperatively applied laser than cryotherapy. The ease of closure depends on the retinal contact area and the position of the break. Whilst superior breaks are easily closed, inferior breaks require more positioning aided by a larger bubble whilst adhesion is established. Gas kinetics are therefore key to considering the efficacy of tamponades.

To assess air and various diluted concentrations of C2F6 or C3F8 as potential substitutes mimicking 20% SF6, we used a validated simulated model of gas kinetics in human eyes [17, 18]. We calculated predicted maximum volumes, time to maximum volume, duration of gas in vitreous cavity and percentage gas fill on various days postoperatively with the corresponding retinal contact angle using data from Fawcett et al. [19]. 4.0, 7.2 and 10.0 ml vitreous cavity volumes were used to represent hypermetropic, emmetropic and myopic eyes respectively [20]. We assumed a 75% fill of the vitreous cavity was achieved at the time of surgery.

16% C2F6 and 12% C3F8 were used as reference due to their isovolumetric concentration commonly used as a tamponade in vitrectomy for RRD repair [21].

A table of different concentration of F-gases injected in a 7.2 ml vitreous cavity was produced (Table 1). The calculations were repeated for 4.0 ml and 10.0 ml vitreous cavities (Supplementary Table 1 and 2). Figure 1a shows the data plotted for air, 20% SF6, 8% C2F6 and 6% C3F8 in a 7.2 ml vitreous cavity. Figure 1b shows the first 10 days with the corresponding retinal contact angle in Fig. 1c. Figure 2 shows an illustration example of a 75% gas fill in vitreous cavity having retinal contact angle of 210°.

Table 1 Predicted percentage gas fills and retinal contact angles in a 7.2 ml vitreous cavity.
Full size table
Fig. 1: Gas kinetics with corresponding retinal contact angle.
figure 1

a Plot of air, 20% SF6, 8% C2F6 and 6% C3F8 in a 7.2 ml vitreous cavity. b Close up view of first 10 days of a. c Corresponding retinal contact angle graph for b.

Full size image
Fig. 2
figure 2

Illustration example of a 75% gas fill in vitreous cavity having retinal contact angle of 210°.

Full size image

It can be seen that ‘isovolumetric’ is a misnomer, as all gases, other than air expand slightly after insertion due to the transfer of blood gases based on their partial pressures. 20% SF6 achieves a greater gas fill on days 1–2 but quickly declines to a lower fill than dilute C2F6 and C3F8 by days 2–3. The gas dynamics of C2F6 and C3F8 are quite distinct. For the same concentration, C3F8 takes twice the time of C2F6 to achieve a similar maximum volume and lasts around 1.7 times longer in the vitreous cavity. On day 7, there will still be a 64% fill of 8% C2F6 and 75% of 6% C3F8, compared to only 46% in 20% SF6. 8% C2F6 takes about 11 days to go below a 50% gas fill, compared to 18 days for 6% C3F8. There is a marked difference in the total duration of tamponade, and dilute mixes of gases have little effect on their duration.

Air achieves considerably lower percentage fills than the F-gases, declining below 50% after day 3, although the retinal contact angles show a less dramatic decline.

It should also be noted how these parameters vary by ocular size. Although percentage fill varies little, gases persist longer in larger eyes due to higher absolute gas volumes, explaining the variability between series dependent on the refractive case mix [8].

The results show that the tamponade characteristics of 20% SF6 cannot be mimicked completely using weaker concentrations of C2F6 and C3F8. They maintain a greater fill for significantly longer and last approximately twice and three times as long respectively. However, the extent of retinal contact is similar for the first 7 days. Similarly, whilst air resolves rapidly, it maintains a retinal contact angle of over 140 degrees for the first 5 days based on a modest 75% fill at baseline, enough to close even inferior breaks with suitable positioning allowing laser-treated breaks to form a permanent adhesion.

Traditionally, gas use in RRD repair by vitrectomy is highly subjective, with SF6 used for superior breaks and C2F6 and C3F8 preferred for inferior pathology [22]. Although only clinical studies can assess the equivalence of these options in terms of retinal re-attachment, knowledge of gas dynamics can inform tamponade choice based on factors such as retinal break position(s), posturing abilities, and other commitments (work or carer responsibilities) or planned flights.

Other surgical procedures for RRD repair, namely scleral buckle and pneumatic retinopexy (PnR) could be regarded as ‘greener’ techniques, due to no or lower volume of F-gas being used. Recently, PnR has been compared to vitrectomy in treating RRD, with evidence suggesting it may give improved visual results in macular-involving cases, albeit associated with reduced primary success [23]. Scleral buckling similarly has shown improved visual results in phakic medium complexity RRD compared to vitrectomy and possibly with less retinal shift, conveying the same advantages of PnR in macular-involving eyes [24]. Despite that, vitrectomy with tamponade remains the most utilised surgical technique for RRD repair in the UK [7]. Whilst encouraging other techniques in suitable situations, it is nevertheless important to explore ways to reduce our carbon footprint whilst performing vitrectomy.

In conclusion retinal surgeons should consider the use of air, weaker concentrations of C2F6 and C3F8 in selected cases to replace SF6 during vitrectomy. Scleral buckling and PnR should also be considered where appropriate. Careful audit, with case pooling using initiatives such as the BEAVRS/Euretina database [25] and future prospective studies will be needed to ensure results are maintained. Other measures to reduce gas wastage include using small volume single-use F-gas canisters instead of traditional large gas cylinders [26], and pre-mixed diluted gas in quantities specific for one eye. The NHS is perhaps uniquely positioned to widely adopt these measures via its national procurement mechanisms.

Although the actual amount of F-gases used by retinal surgeons is low, it has been estimated for each RRD repair, the mean equivalent mass of CO2 per patient range between 2 kg to nearly 120 kg, depending on gas type and gas delivery systems being used [27]. The European Chemicals Agency have released a proposal to limit the use of all per- and polyfluoroalkyl substances which will also include perfluorocarbon liquids (e.g., decalin and octane) and semi-fluorinated alkanes (e.g., F6H8, F4H5). Although exemptions for their use may be obtained, research into alternatives for the fluorinated compounds we use is needed.