About Eye Disorders

LASIK is often used to treat the common refractive eye disorders known as myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. Another common disorder, known as presbyopia, is not correctable by LASIK. Eye doctors measure the severity of the disorder in units called diopters, which represent the amount of correction that would be needed to return the patient to 20/20 (known as “normal”) vision. The higher a prescription reads in diopters, the greater the degree of nearsighted or farsighted vision. Myopia is measured in negative diopters and hyperopia is measured in positive diopters. Diopter measurements are often referred to with the letter "D". For example, -3.00 D means that 3.00 diopters of correction is needed to obtain 20/20 vision.

Myopia:
Ideally, as light rays enter the eyes, pass through the cornea and the lens, they focus directly on the eye’s rear surface, known as the retina. Myopia, or nearsightedness, occurs when the light rays entering the eyes focus in front of the retina instead. This can be caused by the eye being too long, or by a cornea that is too steep or pointed, or by the eye’s focusing mechanism being too strong. The result is that objects nearby are clear, but objects at a distance are blurry.

It is estimated that about 25% of people living in North America (nearly 70 million) are myopic. Almost 90% of people with myopia have a correction level under –6.00 D, or mild to moderate myopia. Precision Laser Eye Center corrects myopia using the Allegretto Wave laser, one of the few lasers able to treat even extreme myopia up to –12 diopters with astigmatism of up to –6 diopters.

The classifications of myopia are shown below.

Mild < -6.00 D
Moderate -6.00 D to -10.00 D
Severe -10.00 D to -15.00 D
Extreme > 15.00 D

Hyperopia:
Hyperopia, or farsightedness, occurs when the light rays entering the eyes strike the retina before coming into focus. This is caused when the eye is too short, has a vertical oval shape, or has a cornea that is flatter than normal, or when the eye’s focusing mechanism is too weak. The result is that objects at a distance may be clear, but objects nearby are blurry. Hyperopia may cause eyestrain or headaches, especially with reading.

Precision Laser Eye Center corrects hyperopia using the Allegretto Wave laser, one of the few lasers able to treat even extreme hyperopia up to +6 diopters with astigmatism of up to +5 diopters, not exceeding a mean spherical equivalent of +6 diopters.

The classifications of hyperopia are shown below.

Mild +1.00 D to +2.00 D
Moderate +2.00 D to +4.00 D
Severe +4.00 D to +5.00 D
Extreme > +5.00 D

Astigmatism:
Astigmatism occurs when the surface of the cornea is shaped more like a football, or is too steep in one place and too flat in another, instead of being spherical. As a result, light is not focused symmetrically on the retina, which causes blurriness or "distortion" at all distances. Slight uncorrected astigmatism may not cause symptoms, but a more severe astigmatism may result in significant blurring and headache. Over half of myopic patients also have mild astigmatism.

Astigmatism will appear as the second number of most glasses prescriptions, for example -3.00 -2.00 x 30. In this case the patient has 2.00 diopter of astigmatism.

The classifications of astigmatism are shown below.

Mild <1.00 D
Moderate 1.00 D to 2.00 D
Severe 2.00 D to 3.00 D
Extreme > 3.00 D

Presbyopia:
As a normal process of aging, the fibers attached to the eye’s lens lose power, elasticity, and the flexibility to change from distance vision to near vision. This condition, known as Presbyopia, usually sets in after 40 years of age, and is treated with reading glasses or bifocals. Presbyopia cannot be treated with laser vision correction.