Introduction
Eyesight problems, medically termed “refractive errors”, are common. With astigmatism, another common refractive error, the light is distracted to multiple areas of the cornea.
Refractive errors can often develop within a few months. They occur mostly in the early teenage years and in the mid 40’s to 50’s. During the teenage years (ages between 10 and 13) the eye ball experiences a great deal of growth. It can genetically grow too long, which is often associated with myopia. In the 40’s it is the aging process that leads to a relative shortening of the eyeball. This is associated with farsightedness (hyperopia) that leads to the necessity of reading glasses.
Signs and Symptoms
Myopia
With uncorrected myopia (nearsightedness) your eyesight would be blurred as shown in this link. Objects in front are in focus, but the objects in the distance are blurred.
Myopia is the visual condition in which only nearby objects appear in focus. This is much like a camera that permanently focuses at a close distance. With nearsightedness and without glasses or optical correction the patient only sees near objects clearly. Only objects that are very close to the eyes are visible to a patient with myopia. Nearsightedness is caused when the eye is too long (axial myopia). Alternatively, when the eye has too much refractive power (refractive myopia) nearsightedness is also possible.
Hyperopia
With hyperopia (farsightedness), however, the patient sees the distance clearly. In this example seen through the eyes of a patient with farsightedness the man up front is not in focus. Note that the tree and the buildings in the background in the distance are clear and focused. The patient has a problem reading a newspaper and the arms feel too short to be able to focus on the print. Reading glasses help the patient to see the print in focus again.
Astigmatism
With astigmatism the surface of the cornea in these patients is not like a perfect globe. Instead it is rather like the asymmetric shape of a rugby ball. This is illustrated in this link. The vision before correction would look like this (uncorrected astigmatis). The image is not in focus either in the front or in the back. All of it is blurred because the cornea has different curvatures. However, after correction for astigmatism the same image looks as shown in this link. The following link explains more about the diagnostic tests regarding astigmatism.
Eyesight Problems
Diagnostic Tests
The simplest test to check the overall vision is a visual acuity test. Using eye charts the doctor or optometrist will determine which of the letters or numbers the patient can still read. If you can still accurately read (20/20 vision is perfect) everything at a certain distance you have perfect vision.
Treatment
Glasses and contact lenses are the main conventional means of correcting visual problems. Most of the visual problems are myopia, hyperopia and astigmatism.
However, the ophthalmic surgeon can treat the patient with operative methods (refractive surgery). But they have their strengths and weaknesses. It is tempting to throw away glasses and contact lenses and have clear vision after refractive surgery. This is what a lot of eye surgery clinics tell you.
There are possible complications with eye surgery
But there are possible complications, such as a certain percentage of cataracts and glaucoma formations following these surgeries. A weakening of the cornea makes the eye more susceptible for rupture with physical trauma. Here is an image of the cornea before and after laser surgery. This shows you that the cornea is thinner after the procedure. If you would like to explore refractive surgeries, discuss this with the eye surgeon carefully. Weigh the pros and cons. For my part I decided to continue to live with glasses.
References
1.The Merck Manual: overview of refractive error
2. Ferri: Ferri’s Clinical Advisor: Instant Diagnosis and Treatment, 2004 ed., Copyright © 2004 Mosby, Inc.
3. Rakel: Conn’s Current Therapy 2004, 56th ed., Copyright © 2004 Elsevier
