There are different standards for different ages. A naked eye vision of 4.9 is abnormal for adults and normal for children of some ages. A naked eye vision of 4.9 is below normal for adults. It is normal for children aged 3 to 5 years. The vision loss may be mild myopia, astigmatism, hyperopia, or corneal scarring due to corneal disease. In the case of older people, it may also be a lens problem, with clouding of the lens or macular degeneration occurring with age. However, some normal people with no other obvious abnormalities on routine eye examination may have a visual acuity of only 4.9. Such cases just need to be kept under observation and no special treatment is required. It is advisable to go to the hospital to find out the cause and correct the problem promptly if vision loss is detected.