The Full Metal EP 253 Schematic Eye is a valuable tool designed to aid students in mastering the art of retinoscopy while offering instructors a means to assess their proficiency. The back of the Schematic Eye can be adjusted within a range from +3 to -4.5 to mimic various refractive errors. By setting the eye to "plus" values, hypermetropia (farsightedness) is simulated, while "minus" values yield myopia (nearsightedness). The addition of a 38mm diameter trial lens in front of the pupil extends this range further.