Validation of Innovative Scheimpflug Topography Derived RGP Contact Lens Designs In Optometry Network

The goal of this Prospective, single-site, cohort study is to validate rigid gas permeable corneal contact lens (RGP) designs for keratoconus derived from combining the data from corneal topography scans and contact lenses ordered in patients with keratoconus (KC) attending a UK tertiary NHS Hospital contact lens clinic. The main questions it aims to answer are: * Does a Scheimpflug topography derived RGP contact lens design for keratoconus have the equivalent overall contact lens fit as the patients' own lens? * Is the number of trial lenses required to fit a patient is reduced compared to standard practice? * Is the time taken to fit a contact lens is reduced compared to standard practice? * Is there user acceptance of the new lens? * Are the Axial ege lift (AEL) changes clinically significant? There will be 3 work packages WP1: For each participant data collection will take place over two visits. • Visit 1: Pentacam topography scans and optimal 'virtual' lens selection will take place. • • Visit 2: Participants are fitted with 4 contact lenses (i) the optimal lens design as specified by the virtual fitting module, (ii) a contact lens with a clinically significant step flatter AEL (iii) a contact lens steeper in axial edge lift (AEL) (iv) the participant's own contact lens. Each CL fit will be assessed with slit lamp photography according to the standardised method proposed by Wolffsohn et al. (2013), Anterior segment OCT MS39) (CSO Hansom Instruments, UK) and best-corrected visual acuity with each lens design using high-contrast logMAR . WP2. Participants will attend one appointment where a traditional lens fit, and a lens fitted using the topography guided 'virtual' module will be undertaken (with the fitting method selected for each eye randomised). For each fitting method the total fitting time will be measured and the total number of trial contact lenses used. Patients will be invited to complete a questionnaire that probes their satisfaction of this pr