Refractive errors are the most common type of eye disorder.
They occur when the shape of the eye does not bend light correctly. This keeps the light rays from focusing properly on your retina. The result is blurred vision, which can be severe enough to cause visual impairment.
About 153 million people worldwide live with visual impairment due to an untreated refractive error. Many people don’t realize their vision could be better. That’s why routine eye exams are so important.
What Causes Refractive Errors?
Refractive errors can be caused by:
- Eyeball length (too long or too short)
- Problems with the shape of the cornea (outer layer of the eye)
- Aging of the eye’s lens
Refractive errors get passed on through genetics. Research shows that environmental factors also play a role. Children and adults who read and look at screens more have higher chances of developing refractive errors.
What are the Symptoms of Refractive Errors?
The most common symptom of refractive errors is blurred vision. Other symptoms include:
- Double vision
- Hazy vision
- Halos or glares around lights
- Headaches or migraines
- Eye strain (soreness or fatigue in your eyes)
- Difficulty focusing (especially when reading or looking at a screen)
4 Types Of Refractive Errors
Refractive errors can be diagnosed easily by an eye doctor during a normal eye examination.
There are four common types of refractive errors:
Astigmatism is when your eye isn’t completely round. This causes up-close and far-away objects to appear blurry.
The most common type of astigmatism is corneal astigmatism. This means that your cornea (the clear outer layer of your eye) is egg-shaped.
The other type is lenticular astigmatism. This means that the lens, which is behind your iris (colored part of the eye), is the wrong shape.
Astigmatism often occurs with myopia (nearsightedness) or hyperopia (farsightedness). Symptoms include:
- Blurry vision far away or close up
- Fluctuating vision
- Difficulty seeing at night
- Glare and starburst patterns around lights
2. Myopia (Nearsightedness)
Nearsightedness makes distant objects appear blurry. You’ll experience poor vision when viewing objects far away. Near vision is usually unaffected.
Myopia occurs when the eyeball grows too long from front to back. Extra curvature of the cornea or a lens that is too thick can also be a cause.
Myopia usually starts developing during childhood and can progress slowly or rapidly. Vision impairment often worsens during childhood and adolescence, then stabilizes in adulthood.
The prevalence of myopia is increasing worldwide. Studies suggest that time spent outdoors may reduce the risk of myopia.
The most common symptoms include:
- Blurry distance vision
- Frequent eye rubbing
- Inability to see the front of the classroom, television, etc.
- Excessive blinking
- Difficulty seeing while driving (especially at night)
- Unawareness of distant objects
3. Hyperopia (Farsightedness)
Farsightedness is very common, with about 25 percent of the population being affected. Hyperopia causes poor vision when viewing objects up-close while distant ones remain clear.
Hyperopia occurs when the eyeball is shorter than it should be. If you need reading glasses, you may have early signs of hyperopia.
Hyperopia is usually present at birth. Some children outgrow it, with the eye’s curvature lengthening to normal. Others stay at the same prescription or develop worse vision.
Common symptoms of hyperopia include:
- Trouble focusing on close items
- Blurry vision
- Fatigue after close-up tasks like reading or computer work
4. Presbyopia (Age-Related Farsightedness)
Presbyopia causes difficulty focusing on close objects, especially while reading. Nearly everyone experiences it at some point after age 40. This decline in visual function comes from age-related changes to your eye’s lens.
Presbyopia is not the same as age-related macular degeneration (AMD). AMD affects the macula, a small spot on your retina, and causes blurry central vision. Presbyopia affects the lens and causes blurriness in the entire visual field.
Common symptoms of presbyopia include:
- Holding reading material or screens farther away
- Blurred vision at normal reading distance
- Eye strain or headaches after close-up work such as reading or computer work
- Worsening symptoms in dim lighting
Additional Refractive Errors
Other refractive errors occur as symptoms of eye disorders and diseases or independently. These include:
Contrast sensitivity is the ability to distinguish between similar shades and patterns. People with poor contrast sensitivity might be unable to tell the difference between an item and its background.
It’s a symptom of several conditions, including:
- Macular degeneration
People with poor contrast sensitivity may experience difficulty in the following situations:
- Driving at night or in poor visibility conditions
- Locating objects against a similarly colored background
- Reading items with poor contrast, such as a newspaper
- Going up or down steps or curbs
- Telling the difference between the facial features of others
Contrast sensitivity treatment depends on the cause of this symptom. Eye drops, eye injections, or surgery are the most common treatment options.
Anisometropia is when two eyes have unequal refractive power, making it difficult to focus. This occurs when your eyeballs, corneas, or lenses are different in each eye.
Different types of anisometropia include:
- Simple anisometropia. When one eye has a refractive error
- Compound anisometropia. When both eyes have refractive errors
- Mixed anisometropia. When one eye is myopic (nearsighted), and the other is hyperopic (farsighted)
- Blurred vision
- Poor depth perception
- Amblyopia (lazy eye)
Anisometropia is treated with corrective lenses, contact lenses, or laser eye surgery.
Aniseikonia is when the size of items is different in each eye. This can occur due to different refractive power in each eye or refractive error correction.
- Balance disorders
Aniseikonia is treated with corrective eyeglasses or contact lenses.
Refractive Amblyopia (Lazy Eye)
A lazy eye may result from a refractive error in one eye but not the other. Or, it may involve opposing refractive errors in the eyes.
Risk Factors for Refractive Errors
Anyone can develop refractive errors, and there’s no way to prevent them. You’re more likely to have a refractive error if your family wears glasses or contacts.
Most refractive errors, including myopia, typically begin in childhood. Some types, such as presbyopia, are more common in adults over 45.
Your eye doctor will recommend a vision screening schedule based on your risk factors and medical history.
How to Diagnose Refractive Errors
Your optometrist or ophthalmologist can diagnose refractive errors during a routine eye exam. They may perform the following tests:
- Visual acuity test. This measures your distance vision
- Refraction test. This determines your prescription for corrective lenses
- Slit-lamp exam. This allows your doctor to examine your eyes’ structures
Diagnosing Refractive Errors in Children
Your pediatrician might detect a problem during your child’s routine vision screening. If so, they’ll refer you to a pediatric eye doctor. You may also notice your child having difficulty at school due to poor vision.
Young children may be unable to read the letters on a typical eye chart. In these cases, your eye doctor may use retinoscopy to diagnose refractive errors. This exam involves observing the way light reflects off the retina.
Refractive Error Treatment Options
Untreated refractive errors can lead to problems, including:
- Worsening vision
- Amblyopia (lazy eye)
- Visual impairment or blindness
The most common refractive error treatment options are:
Prescription eyeglasses can treat most refractive errors. The main types of eyeglasses are:
Single vision lenses correct one field of vision, near or far. Doctors prescribe them to nearsighted or farsighted patients.
Bifocal lenses have separate sections for near and far sight correction. They’re usually prescribed to patients who have presbyopia and an additional refractive error, such as:
Trifocals have sections for near, intermediate, and far-distant correction. The drawback of trifocals and bifocals is that there are lines between each section of vision correction. This can make it difficult for the eye to adjust at first.
Progressive, or multifocal, lenses provide the same correction as bifocal and trifocals. The advantage is that multifocal lenses don’t have lines separating the sections of distance correction.
Contact lenses can also treat refractive errors. There is a large variety of contact lenses available, the most common being:
- Rigid gas-permeable (RGP)
- Daily-wear soft lenses
- Extended-wear disposable
- Planned replacement
Your eye doctor can prescribe contact lenses for different types of vision correction, including:
Refractive Error Correction Surgery
Refractive surgery is becoming increasingly popular. This safe and effective option offers a permanent or more long-term solution than glasses or contacts.
Refractive surgery decreases or eliminates dependency on glasses or contact lenses. Common surgeries include:
- Various methods of remodeling of the cornea (keratomileusis)
- Lens implantation
- Lens replacement
The most common refractive surgeries include:
LASIK (laser in-situ keratomileusis)
LASIK surgery starts with a small flap created using a microkeratome or femtosecond laser. Then the surgeon uses an excimer laser to reshape the cornea.
LASIK can correct common refractive errors, including:
PRK (photorefractive keratectomy)
PRK is a similar procedure to LASIK. Instead of creating a flap, the entire outer layer of the cornea (epithelium) is removed. This grows back in a few days following the surgery.
LRI (limbal relaxing incision)
Limbal Relaxing Incisions (LRI) correct minor astigmatisms. The procedure involves making incisions at the opposite edges of the cornea, following the curve of the iris. This causes a slight flattening in that direction.
ALK (automated lamellar keratoplasty)
ALK is used to correct major myopia or hyperopia. The surgeon uses a microkeratome device to separate a thin layer of the cornea and create a flap.
Then, part of the cornea is removed to flatten it. The results of this surgery are slightly less predictable than LASIK and PRK.
LTK (laser thermal keratoplasty)
LTK uses a holmium laser to heat and shrink the cornea. It is used on patients who have mild hyperopia or astigmatism. The results may be temporary.
CK (conductive keratoplasty)
Conductive keratoplasty is similar to laser thermal keratoplasty, except it uses radiofrequency energy instead of laser energy to reshape the cornea.
CK is more common in the U.S. because its effects are more consistent and last longer.
Intacs (intracorneal ring)
Intacs corneal inserts or implants can treat mild myopia. In this procedure, two small, translucent, crescent-shaped pieces of plastic polymer are inserted into the cornea. This reshapes the eye’s front surface.
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