This paper presents a design methodology targeted on specific functions that a product must perform during its entire life-cycle, with a particular emphasis on realising these functions using additive manufacturing (AM) applications. An ocular speculum is redesigned to reduce surgery time, complications, lower costs and increase customer compliance and functionality. The ocular speculum is a surgical device used for delivering intravitreal injections. Thus, special attention was given to those specific functions that relate to ergonomics of the product and diminishing complications of currently available models. AM is used to test functional prototype specimens in-vivo and for laboratory trials. AM technologies played a key role in manufacturing of the prototypes, fabricating the intricate shapes proposed by the constructive solutions in the FA stages. The case study has both research and industrial value, as it has been developed in collaboration with a UK-based medical device manufacturer. The research results gained validate and further recommend the proposed methodology for other product applications.