The human eye is a complex organ that contains many cells, ligaments and other structures that function together to focus upon an object once light enters the eye. When light does enter the eye, different things happen. For example, some muscles relax while performing a task, while ligaments are pulled tight.
When an eye focuses on an object, it is called accommodation. According to Think Quest, accommodation is defined as changing the “focal length of the lens by changing the curvature of the eye lens.” Accommodation allows images at different distances to be focused on the retina.
When the eye focuses on a near object, the eye must accommodate to be able to see the object clearly. The ciliary muscle contracts, which releases tension on the ligaments that suspend the eye. As a result, both lens surfaces become more curved and the eye thus focuses on the nearby object.
There are several things that happen when the eye focuses on a local object, including the ciliary muscle contracting and the relaxation of the suspensory ligament. Additionally, the crystalline lens becomes thicker, the focal length shortens and light rays converge earlier thus creating the image on the retina. According to the Physics Classroom, “the reduction in focal length will cause more refraction of light and serve to bring the image back closer to the cornea/lens system and upon the retinal surface.”
According to Dr. Ted Montgomery, the closer an object is to the eyes, “the more effort the ciliary muscles must exert for the eyes to focus clearly on that object.” Because of this, more strain is placed on the intraocular muscles, which quite often produces headaches. To help prevent strain on the eyes and even headaches, one should sit up straight when writing, keep reading material away from the eyes when reading and keep an arm’s distance away when sitting at a computer.
Nearpoint stress is defined as stress on the eyes due to extended periods of near work, including reading, surfing the Internet and sewing. Because the eyes work so hard to focus on the near work, by the time you look away to rest your eyes, farther objects appear blurry and would take longer to come into focus. Symptoms of nearpoint stress include eye fatigue, headaches, blurred vision and even a poor ability to concentrate on tasks up close.
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