|
IS REFRACTIVE SURGERY RIGHT FOR YOU?
Millions of people are regaining active lifestyles and preferred occupations with clear vision. Is LASIK right for you?
WHAT IS GLAUCOMA?
Glaucoma is a group of eye disorders that can lead to progressive loss of vision, often without any symptoms.
The eye is a truly amazing organ. Just the size of a ping-pong ball, this complex little globe converts the light around us into vibrant images. While the anatomy of the eye is somewhat complex, its overall function is much like that of a camera. This section will explain how the normal eye works, as well as how lenses (glasses or contacts) correct refractive errors such as nearsightedness and farsightedness.
As shown in the adjacent diagram, light passes through the clear cornea, the front window of the eye, which partly focuses the rays. The pupil, a round opening in the center of the colored iris, dilates and constricts to control the amount of light entering the eye, much like the diaphragm of a camera lens. Next, light passes through the lens of the eye, which sits just behind the iris. The lens further focuses the light, which continues on through the clear vitreous which fills the majority of the eye. Light finally arrives at the retina, a tissue paper thin membrane which lines the inside of the eyeball. The retina is the eye's film, sensing the light we see and converting it into signals which are then sent on to the brain via the optic nerve. The brain, like a computer, further processes information from the retina, creating the images we see.
In the normal eye, distant light rays are precisely focused by the cornea and lens onto the retina, leading to excellent visual acuity, generally 20/20 or better. (This numerical description of visual acuity means that the person being tested can see at 20 feet what a normal sighted person can see at 20 feet. The limit of normal human visual acuity has been determined by study of the eye.) If there is an imbalance between the power of the refractive structures of the eye (cornea and lens) and the eye's length, light will not be properly focused on the retina. Depending on the type of imbalance, either nearsightedness, known as myopia, or farsightedness, known as hyperopia, occurs.
If the cornea/lens power is too strong, or the eye is too long, nearsightedness develops. In this case, a person can see well at near, but distant objects are out of focus. Corrective lenses are required to refocus the light onto the retina in order to improve distance visual acuity (see diagram at left).
On the other hand, if the cornea/lens power is too weak, or if the eye is too short, farsightedness occurs. This leads to poor near vision and better distance vision, though in some cases vision is not clear at any distance without correction (see diagram at right).
Astigmatism develops when the curvature of the cornea or lens is irregular, leading to different refractive powers depending upon the direction of the incoming light. This condition also leads to blurring of vision and is corrected with lenses.
Eyeglasses and contact lenses can both be used to correct refractive errors of the eye. While the choice of glasses or contacts is primarily a personal one, there are some medical considerations. Contact lenses will produce better vision than glasses in certain ocular conditions. However, some people are poor candidates for contact lenses due to ocular diseases such as blepharitis and dry eye syndrome, conditions which are discussed in other sections of the library.
The prescription of eyeglasses requires a procedure known as refraction, during which a series of lenses are passed before the eye in order to measure its refractive error. Once the numerical prescription is determined, frames are chosen, measurements of the eye and face are taken, and glasses can be made. At this point, many options exist in the choice of frame style, lens type, lens coating, etc. More detailed information about these options can be found on the optical shop page, accessible from the home page.
The fitting of contact lenses first requires a refraction, however additional steps are then involved. Measurement of the curvature of the cornea is performed, followed by test fitting of the intended lens on the eye. Once a good fit is determined, adjustments are made to the strength of the lens in order to achieve the best vision. Trial lenses are then worn for a short time and the lens fit is rechecked before the prescription is ordered. Additional information about contact lenses can be found on our optical shop page, accessible from the home page.
In most cases, blurry vision is caused by uncorrected refractive error and is treated by simply changing eyeglasses. However, blurred or distorted vision can be a symptom of many ocular disorders. Only a complete eye examination can determine the exact cause of visual loss. If you have experienced a significant change in vision, contact our office today for an appointment.
Click to return to the library index