Pathophysiology
Clinical meaning
Visual acuity refers to the sharpness or clarity of vision, specifically the ability of the eye to resolve fine detail. It is determined by the optical quality of the eye and the neural processing capacity of the visual system. Light enters the eye through the cornea, which provides approximately two-thirds of the eye's total refractive (light-bending) power. The light then passes through the aqueous humor, the pupil (controlled by the iris to regulate light entry), and the crystalline lens, which provides the remaining one-third of refractive power and adjusts its shape (accommodation) to focus on objects at different distances. The focused light passes through the vitreous humor and strikes the retina, a multilayered neural tissue lining the back of the eye. The retina contains two types of photoreceptors: rods (approximately 120 million, responsible for scotopic or dim-light vision and peripheral vision) and cones (approximately 6 million, responsible for photopic or bright-light vision, color perception, and visual acuity). The macula is a specialized region of the central retina responsible for sharp central vision, and the fovea centralis at the center of...