In the static state of ciliary muscle regulation, parallel light (light from infinite objects) passes through the refractive system (cornea, aqueous humor, lens, vitreous) of the eye, focusing on the upper part of the retina is the emmetropia, focusing on the front of the retina is the myopia, focusing on the back of the retina is the hyperopia, not focusing into a focus, but forming one front and one back two focal lines, which is called astigmatism Light eyes. The above are collectively referred to as ametropia.
Regulation refers to the contraction of ciliary annular muscle and relaxation of suspensory band when looking at near objects, which can make the lens protrude by virtue of its inherent elasticity, strengthen its refractive ability, focus the divergent light of near objects on the retina and form a clear image. Physiologic regulation is used to regulate the near sight of the eye in front of the eye; the far sight will also form a blurred and enlarged spot on the retina because of the far sight. The focus can be moved to the retina by using the regulation to make the vision clear, while the regulation used to regulate the far sight is called non physiological regulation.
Therefore, under normal circumstances, adjustment is required for both near and near vision, and the adjustment is closely related to distance. The amount of adjustment is the reciprocal of distance. For example, 1.00d adjustment is required for an object with a distance of one meter in front of eyes, and 2.00d adjustment is required for an object with a distance of 0.5m in front of eyes. If there is ametropia, the adjustment amount of near vision is the sum of the degree of ametropia and the reciprocal of distance. For example, one meter object of – 1.00d myopia does not need to be adjusted, and one meter object of + 1.00d hyperopia needs to be adjusted by 2.00d