What Are the 4 Main Refractive Errors?

Refractive errors can be corrected with eyeglasses, contact lenses, or refractive surgery.

Refractive errors are vision problems that occur when the shape of the eye prevents light from focusing properly on the retina, the light-sensitive tissue at the back of the eye.

1. Myopia (nearsightedness)
   • Close objects appear clear, but distant objects appear blurry. It occurs when the eyeball is too long or the cornea (the clear front part of the eye) is too curved, causing light rays to focus improperly on the retina.
   • Eyeglasses or contact lenses that have a concave shape help refract the light correctly.
2. Hyperopia (farsightedness)
   • Distant objects appear clear, but close objects appear blurry. It occurs when the eyeball is too short or the cornea is too flat, causing light rays to focus behind the retina instead of on it.
   • Eyeglasses or contact lenses that have a convex shape help refract the light correctly.
3. Astigmatism
   • The cornea is misshapen, causing light rays to focus unevenly on the retina, causing distortion or blurriness in vision at all distances.
   • Eyeglasses or contact lenses that have a cylindrical shape help refract the light correctly.
4. Presbyopia
   • A natural age-related condition that affects the ability to focus on close objects. It occurs when the lens of the eye becomes less flexible, making it harder to focus on close objects. Presbyopia usually becomes noticeable in people older than 40 years.
   • Eyeglasses or contact lenses that have a multifocal design or with monovision contact lenses allow each eye to focus on a different distance.

1. Blurred vision: The most common symptom of refractive errors.
2. Difficulty reading: People with myopia may have difficulty reading small print or seeing objects in the distance.
3. Difficulty seeing at night or in low-light conditions: The pupil dilates (gets bigger) due to refractive errors and causes more blurring of the image.
4. Double vision: Two images of the same object are seen side by side.
5. Eye strain or fatigue: When reading or doing other activities that require close vision.
6. Headaches: Especially after prolonged periods of reading or computer use, refractive errors may cause headaches due to the strain on their eyes.
7. Squinting: To see more clearly.
8. Sensitivity to light: Especially to bright light or glare.
9. Seeing halos around lights: Especially at night.

If you experience any of these symptoms see an eye doctor for a comprehensive eye exam to determine if you have a refractive error.

The exact causes of these refractive errors are unknown. They can be inherited and are often influenced by environmental factors, such as working long hours that strain the eyes or reading in low-light conditions.

• Genetics: A person's genes can play a role in the development of refractive errors. If someone has a family history of a particular refractive mistake, they could be more likely to develop that condition.
• Age: Aging causes the lens of the eye becomes less flexible and the shape of the eye may change, leading to a refractive error.
• Underlying health conditions: Diabetes and high blood pressure can cause changes in the shape of the eye and lead to refractive errors.
• Eye injury or surgery: An injury to the eye or certain types of eye surgery can alter the shape of the eye and cause refractive errors.
• Environmental factors: Prolonged use of computers, televisions, and other screens, and reading and writing can contribute to refractive errors.
• Pregnancy: Hormonal changes can lead to refractive errors.
• Nutritional deficiencies: Vitamin A deficiency can cause refractive errors.
• Certain medications: Corticosteroids can change the shape of the eye and lead to refractive errors.

Refractive errors are pretty common and can affect people of all ages. However, certain groups of people could be more at risk of developing refractive errors. These include:

• Children and teenagers: Because their eyes are still growing and developing.
• People who engage in certain activities: High levels of visual concentration, such as reading or sewing, could be more at risk of developing refractive errors.

Regular eye exams can detect and correct refractive errors early on. This can help prevent vision problems and ensure that your eyes are healthy.

Refractive errors are diagnosed through a comprehensive eye exam and typically includes the following steps:

• Visual acuity test: This involves reading an eye chart to determine how you can see objects at various distances.
• Refraction test: The eye doctor will use a phoropter to measure the amount of refractive error in your eyes. You will be asked to look through the phoropter at an eye chart while the doctor changes the lenses and asks you which set of lenses is clearer.
• Slit-lamp examination: The eye doctor will use a slit lamp to examine the front of your eye, including the cornea, iris, and lens.
• Dilated eye exam: The eye doctor will use drops to dilate your pupils so they can get a better view of the back of your eye. This will allow them to check for any signs of problems, such as cataracts or retinal detachment.
• Tonometry: Measures the pressure inside your eye, which can indicate glaucoma.
• Visual field test: Measures your peripheral vision to check for blind spots or other abnormalities.

In addition to these tests, the doctor may ask about your medical history and symptoms, such as difficulty reading, eyestrain, or headaches. They may check your eye movements and alignment to ensure that your eyes work together correctly.

Generally, refractive errors can be corrected with eyeglasses, contact lenses, or refractive surgery, such as laser-assisted in situ keratomileusis. With proper treatment, most people with refractive errors can achieve good vision and quality of life. However, if left untreated, refractive errors can lead to other vision problems and may even cause permanent vision loss.

There are several treatment options for refractive errors, which include:

• Eyeglasses
  • The most common treatment for refractive errors. They work by correcting how light enters the eye, improving vision.
• Contact lenses
  • Are thin, transparent discs that are placed directly on the surface of the eye. They work by correcting the way light enters the eye and can be a good alternative to eyeglasses for active people who do not want to wear eyeglasses.
• Glasses or contacts with progressive lenses
  • Eyeglass lenses with multiple prescriptions in one lens allow for a more natural progression of focus from distance to near. These lenses can be helpful for people with presbyopia.
• Refractive surgery
  • A surgical procedure to correct refractive errors. There are several different types of refractive surgery, which include:
    • Laser-assisted in situ keratomileusis
    • Photorefractive keratectomy
    • Phakic intraocular lenses
  • These procedures involve reshaping the cornea to correct vision problems. These procedures are generally safe and effective, but they may not be suitable for everyone and have some risks and side effects.
• Orthokeratology (Ortho-k)
  • Also called corneal reshaping therapy and is a nonsurgical treatment option that uses special contact lenses to gently reshape the front surface of the eye (cornea) while you sleep.
  • It corrects refractive errors, and the effect lasts a day or two after the lenses are removed. Ortho-k is a temporary treatment that requires ongoing use of the lenses to maintain the product.
• Corneal refractive therapy (CRT)
  • A non-surgical treatment that involves wearing special gas-permeable contact lenses while sleeping. Like ortho-k, CRT lenses gently reshape the cornea to correct refractive errors, but the effect lasts for a more extended period.
  • CRT is a temporary treatment that requires ongoing use of the lenses to maintain the effect.
• Vision therapy
  • Involves a series of exercises and activities designed to improve visual skills and eye coordination. It can be helpful for people with convergence insufficiency or accommodative dysfunction.
• Pinhole glasses
  • Eyeglasses with small holes in the lenses allow only a narrow beam of light to enter the eye. They improve vision by reducing the amount of light that is scattered in the eye. Pinhole glasses are not a replacement for other refractive error treatments, but they can be a useful addition in some cases.

Discuss the available treatment options with an eye care professional to determine the best treatment plan for your specific needs. Individuals with refractive errors need to get regular eye exams and follow their eye care professional's recommendations for treatment.