Eyesight Problems

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[edit] Eyesight problems (refractive errors)

Introduction:

Eyesight problems, medically termed "refractive errors", are common. They can often develop within a few months and they occur mostly in the early teenage years and in the mid 40's to 50's.

In the ages between 10 and 13 when the eye ball experiences a great deal of growth and can genetically grow too long, this is often associated with myopia (nearsightedness, runs in families ). In the mid 40's to early 50's the aging process leads to a relative shortening of the eye ball and this is associated with hyperopia (far-sightedness).

Signs and symptoms:

With uncorrected myopia (nearsightedness) your eyesight would be blurred as shown in this link. Objects in front would be in focus, but the landscape in the background is not. Myopia is the visual condition in which only nearby objects appear in focus, much like a camera permanently focused at a close distance (Nearsightedness = without glasses or optical correction only near objects, typically when held very close to the eyes, are sighted). Nearsightedness is caused by either the eye being too long (axial myopia) or eye having too much refractive power (refractive myopia).

With hyperopia (farsightednes), however, the patient sees the distance clearly. In this example seen through the eyes of a patient with farsightedness the girl up front is not in focus. Note that the background in the distance is 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.

With astigmatism the surface of the cornea in these patients is not like a perfect globe, but rather like the asymmetric shape of a rugby ball. This is illustrated in this link. The same image as shown above is not in focus in the front or back. All of it is blurred because the cornea has different curvatures. There are tests for astigmatism and other more sophisticated tests that will determine the exact type of astigmatism that the patient has and this will allow the optometrist or ophthalmologist to correct the astigmatism.

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 you can still accurately read (20/20 vision is perfect) at a certain distance. Here is another site that explains this.

Treatment:

Glasses and contact lenses are that main conventional means of correcting visual problems such as myopia, hyperopia and astigmatism.

However, there are operative methods (refractive surgery) that can now be used, although they have their strengths and weaknesses. Several effective options for laser refractive surgery are available. Navigating the complex array of options can be difficult. LASIK is lamellar laser refractive surgery in which the excimer laser ablation is done under a partial-thickness lamellar corneal flap. In Epi-LASIK & LASEK the excimer laser is used to ablate the most anterior portion of the corneal stroma. These procedures do not require a partial thickness cut into the stroma. It is tempting to throw away glasses and contact lenses and have clear vision after refractive surgery (so the commercial goes). But there are possible complications, such as a certain percentage of cataract and glaucoma formation following these surgeries and a weakening of the cornea making the eye more susceptible for rupture with physical trauma. If you would like to explore refractive surgeries, discuss this with the eye surgeon carefully and weigh the pros and cons.

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Eye diseases

References:

1. The Merck Manual: Eye disorders

2. Eye conditions: http://www.stlukeseye.com/Conditions/

3. Karolinska Institute Library eye disease links

4. Ferri: Ferri's Clinical Advisor: Instant Diagnosis and Treatment, 2004 ed., Copyright © 2004 Mosby, Inc.

5. Rakel: Conn's Current Therapy 2004, 56th ed., Copyright © 2004 Elsevier