Controlling vision defects

• The eye focuses on near or distant objects by changing the shape of the lens, a process called accommodation.
• The lens is surrounded by a circular muscle called the ciliary muscle, which is connected to the lens by fibers called suspensory ligaments.
• When the ciliary muscle contracts, the suspensory ligaments loosen, making the lens thicker and refracting light waves more strongly.
• When the ciliary muscle relaxes, the suspensory ligaments are pulled tight, making the lens thin and only slightly refracting light waves.
• Light from distant objects needs to be focused only a relatively small amount, so in this case the ciliary muscle relaxes and the suspensory ligaments are pulled tight, making the lens thin and allowing light waves to focus to a point on the retina.
• Light from near objects needs to be focused a large amount, so in this case the ciliary muscle contracts, causing the suspensory ligaments to loosen, making the lens thicker and refracting light waves more strongly, preventing light waves from focusing to a point on the retina.
• People with long sight can see clearly at a distance but have difficulty focusing on nearby objects, often due to an eyeball that is too short.
• Long sight can be treated by using glasses with convex lenses, which partially focus the light before it enters the eye.
• People with short sight can see clearly at close range but have difficulty focusing on distant objects, often due to a too-long eyeball.
• Short sight can be treated using glasses with concave lenses, which partially unfocus the light before it enters the eye.
• Instead of using glasses, people can also use hard or soft contact lenses, which sit on the eyeball and refract the light in the same way as glasses.
• Laser surgery can be used to change the shape of the cornea so it refracts the light to a greater or lesser extent.
• In some cases, the lens inside the eye can be replaced using an artificial lens.