Anatomy of the Eye

Cornea - The transparent front part of the eye, often referred to as the window of the eye. It provides most of the focusing power when light enters your eye. It is composed of 5 layers of tissue. The outer layer (epithelium) is the protective layer. The epithelium is highly regenerative and has the ability to grow back within 3 days. It allows for fast healing of superficial injuries. Most of the inner layers provide strength to the eye. The laser procedure is performed on this part of the eye.

Anatomy of the Eye

Lens - The lens is a clear structure located behind the pupil. The primary function is to provide fine-tuning for focusing and reading. The lens performs this function by altering its shape to become thinner or thicker as necessary. Between the ages of 40 and 50, the lens becomes less flexible. Later in life the lens can become cloudy and hard (cataract formation), and may cause blurring of vision.

Pupil - The black circle. The primary function of the pupil is to control the amount of light entering the eye. When you are in a bright environment, the pupil becomes smaller to allow less light in. In the dark, it expands to allow more light to reach the back of the eye.

Iris - The colored part of the eye. The primary function is to control the size of the pupil. This is achieved by the muscles of the iris.

Vitreous body - A gel substance inside the eyes cavity. It provides a spherical shape to the eye.

Optic Nerve - Carries images from the retina to the brain.

Retina - Consists of fine nerve tissue which lines the inside wall of the eyes and acts like the film in a camera. It transmits images to the brain. When your vision is perfect (emmetropia) the light rays will focus precisely on this part of the eye.

Sclera - White part of the eye. Provides structure, strength and protection to the eye.

Vision Disorders

Myopia or Nearsightedness

Myopia is the medical term for nearsightedness. Myopia occurs when an eye is too long for the cornea's curvature. Light rays enter the eye and do not come to focus on the retina. They come to focus in front of the retina and this produces a blurred image.

The term "nearsighted" means that you can see "near" objects clearly without your glasses but distance vision is blurry. Myopic prescriptions can vary from mild to extreme. The more myopic you are, the more blurred objects appear in the distance resulting in a higher eyeglass prescription and thicker glasses.

A myopic or nearsighted prescription is a negative prescription, i.e., -3.00 -.50 x 180.

Myopic Eye

Hyperopia or Farsightedness

Hyperopia is the medical term for farsightedness. Hyperopia occurs when an eye is too short for the corneas curvature. Light rays will enter the eye and focus behind the retina producing a blurred image.

The term farsightedness means that you may see far objects more clearly without your glasses, but objects close up appear blurry.

A hyperopic or farsighted prescription is a positive prescription, i.e., +2.00 +.25 x 70.

Hyperopic Eye


Many patients with myopia or hyperopia also have some degree of astigmatism or ovalness to their cornea. Astigmatism occurs when the cornea is more oblong than spherical. As a result, patients with astigmatism experience distortion or tilting of images because of unequal bending of light rays entering the eye. Astigmatism is a common condition and occurs in many patients. Patients with high degrees of astigmatism have blurred vision for both near and distant objects.

Astigmatic Eye


Typically, occurring in people over 40, Presbyopia is the normal loss of near vision. The lens loses some of the flexibility that allows to fine tune the focusing of light. Laser vision corrections such as iLASIK and PRK are designed to reshape your cornea and does not affect the lens of your eye, so cannot correct presbyopia.



Refractive disorders of the eye such as Myopia (nearsightedness), Hyperopia (farsightedness), Astigmatism and Presbyopia are measured in units called diopters. Diopters represent the amount of correction you need to normalize your vision. The more nearsighted, farsighted or astigmatic you are, the higher your prescription will be in diopters.

A prescription is written in three numbers:

  • Myopic prescription: -3.50 -.75 x 90. The first number (-3.50) identifies the degree of nearsightedness. The second number (-.75) identifies your degree of astigmatism. The third number (90) is the axis, which indicates the direction of your astigmatism.
  • Hyperopic prescription: +2.00 +.25 x 70. The first number (+2.00) identifies the degree of farsightedness. The second number (+.25) identifies the degree of astigmatism. The third number (70) is the axis, which indicates the direction of your astigmatism.

Treatments Available

Horizon Laser Vision Center offers various laser treatment options for your vision needs. Contact us today to schedule an appointment with one of our specialty doctors!