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What is a refractive error? With refractive errors, the shape of the eye prevents light from focusing on the retina. Factors include the length of the eyeball (either longer or shorter) or changes in the shape of the cornea or lens.
Myopia, otherwise known as nearsightedness, is a vision condition in which you can see close objects clearly, but objects farther away are blurred. Light is focused in front of the retina.
Hyperopia, or farsightedness, is a vision condition in which distant objects are usually seen clearly, but close objects do not come into proper focus. Light is focused behind the retina.
Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or the curvature of the lens inside the eye. The cornea of a normal eye is curved like a basketball. An eye with astigmatism has a cornea that is curved more like a football, with some areas that are steeper or more rounded than others. This may cause images to appear blurry and stretched out. In astigmatism, light is bent differently and is focused at various locations on the retina.
Presbyopia is an age related condition where there is a gradual loss of the eye’s ability to focus on near objects.
Diagnosis of refractive errors can be made by a comprehensive eye examination. Eye examinations are important for all children and adults, starting at 6 months of age. An eye examination will ensure that you can see clearly and comfortably at all distances and detect conditions that may contribute to eyestrain. If needed, glasses, contact lenses or refractive surgery can provide clear and comfortable vision.
~ Melissa Barnett, OD, FAAO
California Optometric Association
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Have you ever felt like you were not quite sure what just happened at your optometrist’s office? It is difficult enough to answer the “which is better, one or two?” questions and then at the end of the exam to try and understand the doctor’s explanations with difficult optometry terms without secretly worrying that you might have said something wrong!
Hopefully this blog will help you better understand some of the more common terms we use in our examinations.
1) First of all, most comprehensive exams will include a detailed case history. The doctor will want to know your family medical and ocular (eye) history. Some terms you may hear include the most common eye diseases – cataracts, glaucoma and macular degeneration.
- Cataract is the term used when the natural lens of your eye becomes cloudy, causing blurred and distorted vision.
- Glaucoma is the eye disease that causes your eye to have excessively high pressure, which can lead to long-term damage of the nerve in the eye.
- Macular degeneration is a disease that affects your central or straight ahead vision.
Not only will the optometrist ask you about a family history of any of these conditions, they will also assess your eye health and your possible risk for developing any of them.
2) Next, the optometrist will perform a refraction to get you the best possible glasses or contacts that will correct your vision.
- A refraction is just the process of determining for each individual what are the best lenses to give you maximum visual clarity and comfort at both distance and near.
- Myopia – nearsightedness or the ability to see better at near than at far.
- Hyperopia or farsightedness, really means that it is more difficult to focus at near and at far distances.
- Astigmatism: this refers to the shape of the front surface of the eye being more football shaped rather than basketball shaped.
3) There are a few terms you might hear specifically in an child’s exam.
- Pursuits: slow, smooth eye tracking.
- Saccades: fast reading eye tracking.
- Accommodation: focusing.
- Binocularity: the ability of the eyes to work together as a team.
4) Finally, there are some terms regarding glasses that it might help to define.
- Progressive lenses are the kind of “no line bifocal” that you might hear about on TV. But, unlike a bifocal, where there are two areas of vision, near and far, progressives have an unlimited amount of areas as you look from distance to near in the lens.
- Transition lenses are the kind that change to dark outside. They undergo an anti-reflective treatment, which eliminates all glare and allows for crisper vision, especially at night.
Hopefully, this quick explanation helps with some of the confusing terms in an eye exam. As for any others, always ask your optometrist to explain something that does not make sense.
~Lisa Weiss, OD, MEd, FCOVD
California Optometric Association
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Astigmatism is a term used by optometrists to describe a prescription for one eye that needs two powers to bring it into focus. It is not a disease or something that will make you go blind, but it can make things blurry at distance and at near.
Most people are familiar with the terms “near-sighted” and “far-sighted.” In the eye care world we use the term “myopia” for near-sightedness and “hyperopia” or “hypermetropia” for far-sightedness. These terms are used to describe the power (+ or -) of the lens needed to make you see clearly.
If your prescription needs only one power to bring your eye into focus then you can think of it as being simple. So if your prescription has a number like -4.00, then you have simple myopia. Similarly, if you have a prescription of +2.25, then you have simple hyperopia.
If you have an astigmatism in your eye, then you have two powers that need to be corrected for you to see clearly. Having an astigmatism in your eye is our way of describing a compound prescription. Instead of just one simple power like we described earlier, there are two powers together. Depending on your prescription, you can have myopia with astigmatism or hyperopia with astigmatism.
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A common example optometrists use to describe astigmatism to patients is the difference between a basketball and a football. A basketball is nice and round, and has only one curve for the entire ball. You can think of that curve as a lens power. A basketball is a good example of a simple prescription. A football, on the other hand, has two curves. This is like an eye that has two powers or an astigmatism.
Astigmatism is not an eye disease, but rather a term we optometrists use to describe a compound prescription in one eye. So don’t be alarmed if your optometrist tells you that you have some astigmatism in your eyes. You are not alone – I have an astigmatism in both of my eyes and I see extremely well!
~Ranjeet S. Bajwa, OD, FAAO
California Optometric Association