Visual acuity of 4.9 cannot be directly used to deduce the degree of myopia and other refractive diseases, if you need to clarify the degree of refraction, we recommend optometry. Usually people say “how many degrees” is the refractive error, there is no conversion relationship between refractive error and visual acuity, through the vision examination can be timely detection of refractive abnormalities, but the specific refractive error needs to carry out a professional optometry examination. Normal adult naked eye visual acuity level is around 5.0, visual acuity of 4.9 is not within the normal range, there may be myopia and other conditions. After refraction, if the refractive error is more than -50 degrees, it suggests the presence of myopia. Vision can be improved by wearing glasses or corneal reshaping lenses, or by undergoing corrective surgery. Abnormal visual acuity results should be further examined to determine the exact cause and treated under the guidance of a doctor.