5. The overall impairment percentage granted to an accident victim with nondisfiguring injuries to symmetrical organs is determined by totalling the percentages of the impairments resulting from each injury and by adding the lowest of those percentages thereto.
Where an accident victim is already handicapped because of a previous accident, a congenital disability or a pathological condition, the sequelae of the previous injury are evaluated exclusively for the purpose of the computation referred to in the preceding paragraph.