The process of determining and correcting the refractive error of a patient is called refraction. At first an objective assessment of the refractive error is done by retinoscopy. This chapter covers the basics of refraction in the eye, errors of refraction, and errors of accommodation. The total refractive power of the eye is 58–60 dioptres. The refractive power of the cornea is 44–45 dioptres. The refractive power of the lens is 15-16 dioptres. Errors of refraction are myopia, hypermetropia, astigmatism, and anisometropia. In this chapter, 35 questions are provided along with their answers.