Accommodation refers to the way our eyes keep things in focus by simultaneously changing the shape of each lens. The result is sharp images of the world regardless of whether things are close by or in the distance.
- If you look into a mirror, the lens in each eye is located just behind the pupil. The lens shape is controlled by ciliary muscles.
- The distance of objects of interest to an observer varies from infinity to next to nothing but the image distance always remains the same.
- Image distance is measured between the retina (the light-sensitive surface at the back of the eye) and the cornea (the transparent surface at the front of the eye) and is fixed in the case of the human eyeball.
- Because the image distance is fixed, our eyes accommodate for this by using the ciliary muscle to alter the focal length of the lens. This enables images of both nearby and far away objects to be brought into sharp focus on the retinal surface.
- The ciliary muscle forms a ring of flexible tissue around the edge of each lens in the eye’s middle vascular layer.
- Our eyes accommodate nearby objects by forming each lens into a shape with a shorter focal length. In this case, the ciliary muscles squeeze the lens into a more convex form.
- Our eyes accommodate distant objects, by relaxing the ciliary muscles, causing the lens to adopt a flatter and less convex shape with a longer focal length.