What is meaning of +- 4D in eye for job application requirement

power 4dSuperconcentrado Redensificador reafirmante-antiedad de Casmara. Fórmula avanzada que redensifica y redefine los contornos faciales. Casmara Power Lift 4D se compone deTwo lenses have power of (i) + 2 d (ii) -4D. What is the nature and focal length of each lens? b. An object is kept at a distance of 100 cm from lens of power -4D. Calculate the image distance.