The functions of the eye constantly adjust the amount of light, focuses on objects near and far, and produce continuous images that are instantly transmitted to the brain. Focused by the cornea and the crystalline lens, the light makes its way to the retina. The eye’s retina contains millions of tiny light-sensing photoreceptor nerve cells called rods and cones, which are named for their unique shapes. Rods primarily contribute to night-time vision whereas cones primarily contribute to the day-time vision. Rods are responsible for perceiving the size, shape, and brightness of visual images. Cones are responsible for color vision and function best in relatively bright light.
When the rays of light moving through an object incident to the eye lens pass through the cornea, the eye lens makes a real and inverted reflection of the object on the retina. The message of reflection is sent to the brain by the light nerves so that this reflection is visible directly on the basis of brain experience.
The Focus Distance of the Eye Lens
The distance between the human eye lens to the retina is called the focus distance of the eye lens, it varies depending on the adjustment capacity of the human eye.
Functions of the Eye: Adjustment Capacity of the Human Eye
The rays of light coming from an object make its reflection on the retina with the help of an eye lens. The distance of the object from the eye keeps on changing. For the reflection to remain on the retina itself, it is necessary that the focus distance of the eye lens be reduced and increased as needed. The ability of the eye muscle to change the focus distance of the lens as per the need is called the adjustment capacity of the eye.
The Far Point of the Eye and the Maximum Distance of Clear Vision
The point located at the maximum distance from the eye that the eye can see clearly without adjustment capacity is called the far point of the eye. The distance from this point to the eye is called the maximum distance of clear vision. Its value is infinite for the healthy functions of the Eye.
Close Point of the Eye and Minimum Distance of Clear Vision
The nearest point that the eye can see clearly by applying its maximum adjustment capacity is called the nearest point of the eye. The distance from the eye to this point is called the minimum distance of clear vision. The minimum distance of clear vision for a healthy human being is 25 cm. The distance between the point near the eye and the farthest point is called visual enlargement.