Presbyopia
Introduction
Presbyopia is a progressive reduction in close range focusing power. With age, the eyes lose their ability to focus on near objects. Nearby objects appear blurry. Presbyopia is easily corrected with glasses or contact lenses.
Anatomy
Your eyes and brain work together with amazing efficiency. Light rays enter the front of your eye and are interpreted by your brain as images. Light rays first enter your eye through the cornea, the “window” of your eye. The cornea is a clear dome that helps your eyes focus.
The anterior chamber is located behind the cornea and in front of the iris. The anterior chamber is filled with a fluid that maintains eye pressure, nourishes the eye, and keeps it healthy. The iris is the colored part of your eye. Eye color varies from person to person and includes shades of blue, green, brown, and hazel. The iris contains two sets of muscles. The muscles work to make the pupil of your eye larger or smaller. The pupil is the black circle in the center of your iris. It changes size to allow more or less light to enter your eye.
After light comes through the pupil, it enters the lens. The lens is a clear curved disc. Muscles adjust the curve in the lens to focus clear images on the retina. The retina is located at the back of your eye.
Your inner eye, or the space between the posterior chamber behind the lens and the retina is the vitreous body. It is filled with a clear gel substance that gives the eye its shape. Light rays pass through the vitreous humor on their way from the lens to the retina.
The retina is a thin tissue layer that contains millions of nerve cells. The nerve cells are sensitive to light. Cones and rods are specialized receptor cells. Cones are specialized for color vision and detailed vision, such as for reading or identifying distant objects. Cones work best with bright light. The greatest concentration of cones is found in the macula and fovea at the center of the retina. The macula is the center of visual attention. The fovea is the site of visual acuity or best visual sharpness. Rods are located throughout the rest of the retina.
Your eyes contain more rods than cones. Rods work best in low light. Rods perceive blacks, whites, and grays, but not colors. They detect general shapes. Rods are used for night vision and peripheral vision. High concentrations of rods at the outer portions of your retina act as motion detectors in your peripheral or side vision.
The receptor cells in the retina send nerve messages about what you see to the optic nerve. The optic nerves extend from the back of each eye and join together in the brain at the optic chiasm. From the optic chiasm, the nerve signals travel along two optic tracts in the brain, and eventually to the occipital cortex, where you process and perceive vision.
Causes
Presbyopia occurs because of the natural aging process. Presbyopia results as the lens in the eye gradually loses it’s elasticity and ability to focus images on the retina. The condition typically develops around age 40 and slowly worsens over time. People with farsightedness may develop the condition earlier. People with nearsightedness may develop presbyopia later. By age 65, the lenses in the eye lose most of their elasticity.
Symptoms
Presbyopia makes it difficult to see objects close-up. You may find it necessary to hold the newspaper or a book farther away than usual to read. Presbyopia may cause eyestrain and headache.
Diagnosis
Your doctor can diagnose presbyopia with a general eye exam. Your general eye examination will include visual acuity and refraction. Visual acuity testing determines your ability to see near and far distances. Refraction is used to determine the degree of the refractive error. The information is used to write a prescription for glasses.
Your eye examination may also include slit-lamp testing, in which your doctor uses a slit light and a microscope to view your inner eye structures. Your eye pressure may be tested for glaucoma.
Treatment
It is helpful to use more light when reading, hold reading material farther away, or read materials that are written in large print. Presbyopia is easily corrected with glasses or contact lenses. Some people may just need reading glasses. Others may need bifocal lenses. Contact lenses have advanced to include bifocals in each contact lens. In some cases, monovision contact lenses, using one for far and one for near vision, can correct presbyopia. Monovision can also be achieved by surgery techniques that perfect one eye for distant vision and one eye for close-up vision. Laser thermal keratoplasty (LTK), conductive keratoplasty (CK), and LASIK are types of surgeries used to create monovision.
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This information is intended for educational and informational purposes only. It should not be used in place of an individual consultation or examination or replace the advice of your health care professional and should not be relied upon to determine diagnosis or course of treatment.
The iHealthSpot patient education library was written collaboratively by the iHealthSpot editorial team which includes Senior Medical Authors Dr. Mary Car-Blanchard, OTD/OTR/L and Valerie K. Clark, and the following editorial advisors: Steve Meadows, MD, Ernie F. Soto, DDS, Ronald J. Glatzer, MD, Jonathan Rosenberg, MD, Christopher M. Nolte, MD, David Applebaum, MD, Jonathan M. Tarrash, MD, and Paula Soto, RN/BSN. This content complies with the HONcode standard for trustworthy health information. The library commenced development on September 1, 2005 with the latest update/addition on February 16, 2022. For information on iHealthSpot’s other services including medical website design, visit www.iHealthSpot.com.
