BACKGROUND: Understanding the financial and environmental impact of clinical pathways is important for designing sustainable services. This study aimed to compare the cost and carbon footprint of sub-Tenon's and topical anaesthesia for cataract surgery, benchmark minimum topical anaesthesia utilisation rates, and quantify the benefits of increased topical anaesthesia usage in the United Kingdom National Health Service (NHS). METHODS: The cost and carbon footprint of products and staffing for topical and sub-Tenon's anaesthesia for cataract surgery were calculated and applied to National Ophthalmology Database audit data. A mainly process-based approach was used to estimate the carbon dioxide equivalent (CO2e) of product production, usage, and waste disposal. RESULTS: The typical CO2e per case was 0.71 kg for topical anaesthesia and 1.19 kg for sub-Tenon's anaesthesia. Around a third of CO2e was generated by usage of unneccesary equiptment and wasteful practices. The typical cost per case was £14.60-£17.14 for topical anaesthesia, £27.74 for sub-Tenon's anaesthesia performed by an operating department practitioner and £56.15 for sub-Tenon's anaesthesia performed by a consultant anaesthetist. It is estimated that around 25,000 NHS cataract cases could annually be converted from sub-Tenon's to topical anaesthesia, which would reduce the CO2e emissions of services by 12,000 kg while saving £265,000 on product usage and between £63,500 and £773,750 on staffing. CONCLUSIONS: Topical anaesthesia is a cheaper and more environmentally sustainable alternative to sub-Tenon's anaesthesia for cataract surgery. Increased topical anaesthesia usage in cataract services could contribute towards the NHS aspiration of becoming "net zero" by 2040.