Our multi-centre cross-sectional survey of patients has provided insights to the intricacies and overall scale of environmental harm caused by the dry eye disease care pathway. The sample population in this study has severe disease and is therefore not representative of the entire dry eye disease population. Patients included in this study will be on more treatments and will require more face-to-face appointments than typical dry eye disease patients, which will inevitably result in greater environmental damage witnessed by the sample population. However, the perspectives of the patients included in this study are perhaps the most valuable as these patients can comment on most aspects of the care pathway. There were considerably less males (21.7%) than females (78.3%) in our study, which could have affected the results, as some literature suggests that males are less likely than females to adopt green behaviours [32]. The median age of all patients in our study was 64 (25, 87) and there was a fairly balanced spread of multiple indices of deprivation scores across all patients. This is noteworthy, as the Waste and Resources Action Programme (WRAP) has identified a correlation between higher levels of deprivation and lower recycling rates [33].
For the sample population, we can use the figures in Table 1 to calculate the number of eye drop dispensers used and the subsequent amount of plastics disposal per patient per year. Assuming that each single-dose dispenser is used for two applications (one in each eye), the median number of single-dose eye drop dispensers used per patient per year is 639 (0, 12045). Also, assuming that every 10 mL multi-dose eye drop dispenser contains 200 drops, the median number of multi-dose eye drop dispensers used per patient per year is 20 (0, 222.65). When emptied, a single-dose eye drop dispenser weighs 1 g and a 10 mL multi-dose eye drop dispenser weighs 6.5 g. Therefore, the median and range values for the weight of plastic disposal per patient per year are 0.64 kg (0, 12.05 kg) for single-dose dispensers and 0.13 kg (0, 1.45 kg) for multi-dose dispensers. This weight of plastic is equivalent to 64 (0, 1205) and 13 (0, 145) 100 mL plastic water bottles, respectively. When using serum eye drops, patients are advised to open a new bottle each day instead of using the same bottle for multiple days. The average drop size is 0.045 ml, and an empty 3 mL vial weighs 8.3 g. As a result, the median number of serum bottles used per day is 1 (0, 2). This practice leads to an annual plastic disposal of 3 kg (0, 6 kg), which is equivalent to discarding 300 100 mL plastic water bottles. It is important to note that these calculations assume that each eye drop is applied successfully in a single attempt, without any wastage or excess administration, and that all bottles are used until they are empty. However, this is often not the case, and the actual amount of plastic waste generated is likely to be significantly higher than the estimated figures suggest.
The administration of eye drops can also generate travel related emissions. Many patients with severe dry eye disease are elderly and have other co-morbidities such as arthritis, which might explain why 5.4% of patients receive assistance with taking their medications from someone who lives in a separate household. The amount of non-recycled waste and travel related emissions secondary to dry eye disease treatments becomes more pronounced when considering the median number of different types of eye drops and ointments that patients had tried was 10 (1, 50) and the wide variety of other treatments that had been undertaken, as displayed in Fig. 2.
On average across the UK, fridge freezers are the most energy-intensive appliance at home. 17.4% of all patients in our study said they use a separate freezer specifically for storing their serum eye drops. On average, 0.193 kg of CO2 equivalent (CO2e) emissions are produced per kWh of electricity use in UK households and compact freezers consume 234.22 kWh of electricity annually [34, 35]. According to these figures, an additional compact freezer will generate 45.2 kg of CO2e emissions per year. If we assume the average car now produces around 220 grams of CO2e emissions per mile, the storage of serum eye drops in a separate compact freezer at home each year is equivalent to driving 205 miles. It is also noteworthy that fridge freezers release highly potent greenhouse gases when faulty or disposed of incorrectly. For instance, HFC-134a is the most common hydrofluorocarbon found in domestic fridge freezers and has a global warming potential 3,400 times that of CO2 [36].
When asked about the disposal of their dry eye medications packaging, 39.5% of patients said everything goes with their general household waste, 13% said everything goes with their recycling and 51.1% said some items go with their recycling (mostly cardboard boxes and paper instructions). The percentage of items being recycled is limited by the absence of clear recycling instructions on packaging. Other potential barriers for recycling include poor infrastructure and service constraints, socio-economic factors that influence human behaviour and a lack of education and public engagement [37]. The presence of these barriers might explain why only 23.9% of patients were concerned by the environmental impact of their dry eye medications and would like to discuss medications with more eco-friendly packaging at their next appointment. To obtain further information regarding the recyclability of medication packaging, we submitted freedom of information requests to multiple councils across England. Generally, the councils indicated that most primary and secondary packaging items will go through the recycling process, providing they have been properly cleaned and did not previously contain blood products e.g. serum. Polystyrene packers cannot be recycled, and blister packs usually result as waste due to the challenges associated with separating foil and plastic.
The collection and delivery of dry eye disease medications generates significant amount of greenhouse gas emissions. In particular, the serum eye drops delivery service, which 87% of patients in this study utilise, transports serum eye drops to patients across the UK from the centralised NHSBT processing facility in Liverpool. A comprehensive description of this service’s environmental impact has been provided by Latham et al. [28]. The median number of hospital appointments per year that patients reportedly attend for dry eye disease is 3 (1, 15). The most common method of travelling to hospital appointments is by car (62.0%) and the median number of minutes for each return journey is 100 (8, 300). According to the Department for Transport, in 2023, the average CO2e emissions per car was 211.2 grams per mile, and the average driving speed on Local ‘A’ roads across England was 23.0 mph. Therefore, in the feasible scenario that a patient attends three appointments per year and drives 23 mph on average for 100 min for each appointment, the annual CO2e emissions for travelling to hospital appointments for such a patient is approximately 19.4 kg CO2e. This is higher than average carbon footprint for three face-to-face and three virtual geriatric medicine clinic consultations, calculated as 14.5 kg CO2e and 3.0 kg CO2e respectively [38]. Moreover, two trees would need to be planted to offset this amount of Carbon equivalent emissions, since over a 100-year lifespan, each tree will absorb approximately 10 kg of CO2 per year.
31.5% of patients in this study thought having dry eye disease significantly increases their Carbon footprint, 37.0% thought it does not and 31.5% could not decide. This correlates with the findings of a survey of 1858 UK adults, which revealed that only around a quarter (26%) of people believe the NHS is contributing to climate change [39]. The majority (55.4%) of patients in our study thought that plastics disposal was the main source of environmental harm. This message is demonstrated in Fig. 4, which shows that environmentally friendly packaging is the strategy that patients would like to prioritise most.
This multi-centre observational study is the first to ascertain the perspectives of patients on the environmental harm associated with severe dry eye disease management. The results of this study are unique and have highlighted multiple areas in which innovations are needed to help the NHS to achieve net-zero. The study is limited by its cross-sectional design and specific sample population. It is likely that the results would have varied if the study was longitudinal and included patients with mild-moderate dry eye disease. Furthermore, the study design is vulnerable to volunteer, response and observer bias. There was a disproportionate percentage of males and females and the number of patients recruited from each centre was also uneven. Despite its shortfalls in methodological robustness and generalisability, this study provides unique insights to the environmental damage that occurs subsequent to the NHS dry eye disease care pathway.
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