Eye Anatomy 101
and Refractive Errors


Our eyes are complex processors of light and images. The cornea, the transparent dome-shaped outermost layer of the eye, acts as a window. As light enters your eye, the cornea bends, or refracts the light, focusing it onto the lens. Your lens then further focuses the light onto the retina, a light-sensing layer of cells that lines the back of your eye. Your retina converts the light to signals, which are then sent to your brain through the optic nerve. Your brain, in turn, interprets these signals as images.

Refractive errors can prevent light from being properly focused onto the retina. If your retina does not receive properly focused light, your brain will perceive images as blurry. Refractive errors occur due to certain anatomical characteristics - specifically anomalies in the length of the eyeball, irregularities in the shape of the cornea or a less flexible aging lens.

Although the most common indicator of a refractive error is blurred vision, an individual may also experience other symptoms, such as halos around light, eye strain and squinting, headaches and double vision.

The Types of Refractive Errors

Refractive errors are the most common vision disorders in the United States. There are four types of refractive errors: myopia (nearsightedness), hyperopia (farsightedness), astigmatism (distorted vision) and presbyopia (aging eyes).

  • Myopia (nearsightedness)
    Nearsightedness1 simply means that close objects are in focus, but distant ones are blurry. The condition results from an elongated eyeball or a cornea that is too steep. Because of these physical attributes, light is focused in front of the retina, rather than directly on it. An inherited characteristic, nearsightedness is often detected in young children and may worsen during adolescence. Once an individual has reached adulthood, there is usually little change. If myopia is severe (high myopia), there is an increased risk of retinal detachment. For this reason, it is important to have regular eye examinations to check for changes in the retina.
  • Hyperopia (farsightedness)
    Farsightedness2 is the opposite of nearsightedness. For the person who is farsighted, close objects are blurry and distant ones are blurry as well. The farsighted eyeball is shorter than normal or the cornea is too flat. Therefore, light is focused beyond the retina rather than directly on it. Like myopia, hyperopia is generally an inherited trait. Farsightedness may not be severe in some individuals and, as a result, they may not perceive their vision as being blurry. However, as the eyes age, farsighted people may begin to notice their vision deteriorating and blurriness becoming more prominent.
  • Astigmatism (distorted vision)
    An individual's vision can be distorted due to an abnormal curvature of the cornea. As a result, light is not focused evenly onto the retina, causing images to appear stretched out and blurry. Astigmatism3 can occur in conjunction with myopia or hyperopia.
  • Presbyopia (aging eyes)
    As we age, the lens becomes less flexible, which inhibits its ability to change shape and focus dynamically on objects. Because the lens cannot adjust, it becomes more difficult to read at close range. Presbyopia4 is normal and affects most people over the age of 40. If an individual is nearsighted, farsighted, or has astigmatism, the pre-existing condition will then combine with presbyopia.

Diagnosis of Refractive Errors at Beach Eye Medical Group

Refractive errors can be diagnosed with a routine eye examination, which includes testing the clarity of vision and evaluating the cornea, as well as the back of the eye.

Clarity of vision, also referred to as visual acuity, is determined using an eye chart. If you have trouble seeing the chart, the examiner will ask you to view the chart with the aid of different corrective lenses. Our eye specialist will then note which lens improves your vision most.

To examine the cornea, our eye doctor will use a slit lamp, which provides a magnified view of the eye. Another instrument, called an ophthalmoscope, is used to check the back of the eye, which contains the retina and optic nerve. In some cases, our eye specialist will administer special eyedrops to dilate the pupils, thus making it easier to view the retina and optic nerve area.

Correcting Refractive Errors: Eyeglasses, Contact Lenses, and Surgery

Prescription eyeglasses and contact lenses are the two most common ways to correct refractive errors and optimize your vision. For many people, contact lenses offer a safe and effective alternative to wearing glasses. Contact lenses are worn directly on the eye, therefore the whole field of vision will be in focus. For those who participate in sports, this can be an advantage.

Refractive surgery is a procedure that changes the shape of the cornea. At Beach Eye Medical Group we offer the latest refractive surgery technologies for LASIK and LASEK. If your eyesight is blurry or you feel eye strain, email us or call (714) 765-9696 to schedule your appointment.

1 Nearsightedness. Available:
2 Hyperopia (Farsightedness). Available:
3 What Is Astigmatism? Symptoms, Causes, Diagnosis, Treatment. Available:
4 Presbyopia. Available:

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