The eyeball is like a convex lens, which has the function of focusing light. Only by focusing the light on the retina can we see clearly. Myopia is caused by the ametropia of the eyes and the lengthening of the axial length caused by various reasons. It is not clear to see far things, but clear to see near things. Some myopic people have higher refractive power than normal people, and some have normal refractive power, but their eyeballs are longer than normal people, resulting in the high beam focusing only in front of the retina, which needs to be corrected by wearing concave lenses (myopia glasses).
Presbyopia, also known as hyperopia, is a physiological phenomenon, namely presbyopia. The weakening of lens elasticity leads to the decline of accommodation ability, mainly because the vision is not clear. "Flowers don't pick up flowers, forty-eight", presbyopia is not only the elderly, but also many young people have early symptoms of presbyopia, such as decreased zoom ability, which is due to the excessive use of electronic products in recent years.
Presbyopia needs to be corrected with convex lens (reading glasses), and the degree gradually deepens with age, increasing by 50 degrees every five years. At the age of 60, presbyopia generally does not deepen, and the highest degree is +300 degrees.
Myopia and presbyopia cannot cancel each other out. When myopia patients reach a certain age, presbyopia will also occur. They can't cancel each other out Because myopia is ametropia, presbyopia is lens degeneration and loss of elasticity. Although the clinical manifestations of presbyopia in myopia patients are slightly lighter than those in ordinary patients, this offset is very limited. If you are a patient with severe myopia and presbyopia, you should not only use reading glasses, but also use myopia glasses to see things in the distance, which is more troublesome than ordinary presbyopia patients.