Corrective Eye Surgery and The Crystalline Lens
Jul0
The Crystalline Lens
Anatomy; Behind the iris lies the crystalline lens. Also a transparent structure, it consists of a capsule, cells, and fibers. It is often referred to as simply the lens (and is the most important part of the eye dealt with by corrective eye surgery), but in order to avoid confusion with a camera lens, an intraocular lens, and a contact lens we will refer to it by its full name.
Physiology: In order to transmit light, the lens, like the cornea, must be transparent or nearly so. As we get older, the crystalline lens becomes larger and may become cloudy. An opacification in the crystalline lens is called a cataract. What is special about the crystalline lens is its ability to change shape, depending on the activity of the muscles which attach to it. As we will see, this property allows the crystalline lens to assist in the focusing of light. When we start to experience problems with these functions, laser eye treatment can resolve a lot of them.
The Retina
Anatomy: The retina is a complex 10-layered neurological tissue which lines the inside of the eye. It consists of photosensitive light receptors, nerves cells, nerve fibers, blood vessels, and a special group of cells known as the retinal pigment epithelium. At the back pole of the eye is a region known as the macula. It is this specialized area that is responsible for the fine central visual acuity which is so important for driving and reading.
Physiology; There are two kinds of photoreceptor cells in the retina, rods and cones. There are three kinds of cones, each of which contains a unique pigment which responds to a specific wavelength of light. The cones provide color vision and fine visual discrimination, and are concentrated in the macula. The rods, in a complementary fashion, contribute mainly to night vision, perception of movement, and peripheral vision.
When light reaches the retina, it is absorbed by one of these pigments and a chemical reaction ensues. A cascade of events follows which ultimately results in a nerve impulse being sent toward the brain through the optic nerve. When your brain interprets these impulses, originating from rods and cones scattered throughout the retina, you “see”.