Optical defects that involve light improperly focusing on the retina of the eye collectively called Refractive errors are the most frequent eye problems in the U.S. The group of refractive errors include: Hyperopia (Farsightedness) – distant objects are seen clearly and near ones blurred, Myopia (Nearsightedness) – near objects are seen clearly and distant ones blurred, Astigmatism-uneven focus, and Presbyopia-Age-related problem involving near focus.

Significant vision impairment can result from uncorrected or under-corrected refractive errors. Almost all refractive errors can be corrected by eyeglasses or contact lenses. In fact more than 150 million Americans use corrective eyewear to correct a refractive error, contributing to America’s 30 million dollar optical industry. Most problems of vision result from an irregularity in the cornea’s curvature. Normally the cornea (clear-front covering of the eye) is curved equally in all directions and allows light to focus exactly on the retina’s surface. The retina is the light sensitive tissue at lines the back of the eye that takes light rays and changes them into nerve signals that are sent to the brain to register images

Hyperopia is an inherited condition that increases with age affecting the clearness of near objects. With Hyperopia the cornea is too flat or the distance from the cornea to the retina is too short. When light rays coming from a nearby object pass through your eye and do not come into focus before striking the retina what results is blurred vision. The natural lens “fine tunes” the image before it is focused on the retina, located at the back of the eye. The retina captures light images passed through the lens of the eye and sends the images through the optic nerve to the brain. A person with hyperopia needs corrective lenses for reading but, can see to drive

For children who are farsighted, corrective lenses can sometimes be avoided due to the strength of the eye’s natural lenses. If the condition is not addressed, as the eyes get older they lose the natural ability to focus and result in the need for corrective lenses.Children with a high degree of hyperopia may experience non-visual symptoms, such as headaches and a lack of interest in reading. It’s best to get regular eye exams and follow through with any prescribed corrections.

Hyperopia is usually treated with prescription eyewear with convex (outwardly curved) lenses or contact lenses that counteract the vision distortion created by corneas that are shaped too flat. When a more severe correction is necessary, Refractive eye surgery is used to correct farsightedness and involves steepening the cornea. Laser In-Situ Keratomileusis (LASIK) is the most common of these procedures. Other procedures used for surgical correction of hyperopia include Implantable Contact Lenses (ICLs), Clear Lens Extraction (CLE) and Laser Thermal Keratoplasty (LTK). Myopia affects approximately 1 in 5 people and is also an inherited condition affecting the clarity of far objects. When the eyeball is more elongated from front to back or the cornea is too steeply curved and dome-shaped, light rays focus in front of the retina rather than directly at the retina.

Prescription eyeglasses with concave (inwardly curved) lenses or contact lenses that counteract the distortion caused by corneas that are too outwardly curved are used for treatment. Surgical corrections include LASIK, and ICRS or Intrastromal Corneal Ring Segments, tiny plastic arcs that are implanted in the peripheral area of the cornea, causing the center of the cornea to flatten

Astigmatism results from an uneven curvature of the cornea causing distorted vision at near or far distances. It occurs when the eye’s natural crystalline lens scatters light rays instead of providing a centralized point of focus. If you’ve been diagnosed with astigmatism you were probably born with this condition. According to the Textbook of Family Practice (Saunders, 2002), 20% of children have a degree of astigmatism and require prescriptive glasses before adulthood.

Astigmatism can range in condition from very mild with no visual symptoms to severe, causing distorted or blurry vision. Each level of astigmatism depends on the eye’s ability to compensate for the cornea’s irregular curvature. When the eye works too hard to compensate the results are headaches and eyestrain. You can have astigmatism and also be nearsighted, farsighted or presbyopic.

This vision disorder can be treated surgically or non-surgically. Toric lenses are hard or rigid contact lenses commonly used to smooth the eye’s surface however, newly formulated soft contact lenses are also available for certain types of astigmatism. Surgical corrections include LASIK, astigmatic keratotomy (AK), in which a small incision is made to smooth the cornea surface.

Presbyopia occurs when the natural crystalline lens–located behind the pupil-loses some of its ability to change shape or flexibility in order to focus on near objects. The natural lens uses cilliary muscles to help it change shape to accommodate both near and objects that are further away.

Most people after the age of 40 develop presbyopia, usually signaled by a need for reading glasses or bifocals. Presbyopics (people with presbyopia) may not require corrective eyewear as soon as others, because the flatter cornea compensates and may continue to use sharp close-up vision in spite of losing some flexibility.

Innovations in treatment of Presbyopia have occurred over the years. Improvements in both appearance comfort and performance have occurred in recent years. The most versatile of all multifocal designs is Progressive or “no-line” multifocal eyeglasses which graduate from distance to reading power without the lines that exist in standard bifocals or trifocals. Multifocal contact lenses are also available, providing near, interim, and distance vision in one contact lens.

The best treatment is catching a vision condition early by receiving regularly scheduled eye exams by an Optometrist or Ophthalmologist.

Thanks to Takiya Farmer at AC for this article.

This entry was posted on Friday, March 30th, 2007 at 5:20 am and is filed under Your Eyes. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.