Status of binocular vision is evaluated using binoculars and accommodative tests. The results of these tests allow the optometrist to decide or the type of lenses has to be prescribed or whether a vision therapy is required. The aim of this work is to check the accuracy of the measurement of the relative amplitude of accommodation. Relative accommodation amplitude assesses the ability to increase or decrease the accommodation when convergence demand is constant. The eye must be neutralized to take the measurement. Because the test is situated at a distance of 40 cm, it is considered that the convergence is 2'5 am and the accommodation 2'50 D. However, this assumption could lead to important errors in ammetropic subjects due to the eye after neutralization accommodates in the image produced by the lens forms and converges in the position of the effective binocular object . Therefore, it is necessary to set measurement conditions in which the accommodative and convergence stimulus are the same for all subjects. Furthermore, the lenses added on the neutralization to determine the relative amplitude of accommodation do not correspond to the dioptric value of relaxation and stimulation of the eye accommodation. To obtain this value a more precise calculation has to be performed.