ConditionEyes & vision
Refractive Errors
Refractive errors are the most common eye problems: the eye does not bend (refract) light to a sharp focus on the retina, so vision is blurred. The four types are myopia (nearsightedness), hyperopia (farsightedness), astigmatism and presbyopia (age-related loss of near focus). They are diagnosed with a routine eye exam and are easily corrected with glasses, contact lenses or laser surgery. Uncorrected refractive error is the leading cause of vision impairment worldwide.
Also called: Refraction errors, focusing problems, ametropia
At a glance
- What they are
- Focusing errors caused by the shape of the eye, cornea or lens.
- Four types
- Myopia, hyperopia, astigmatism, presbyopia. Many people have more than one.
- Main symptom
- Blurred vision at some distances, with squinting, eye strain and headaches.
- Diagnosis
- Visual acuity chart and refraction test during an eye exam.
- Correction
- Glasses, contact lenses, LASIK or PRK, lens implants.
- In children
- Uncorrected errors can cause lazy eye; myopia can be slowed with specific treatments.
When to get help
Call 911 or go to the ER
- Sudden loss of vision, a dark curtain across vision, or a shower of new floaters and flashes (possible retinal detachment, more common with high myopia)
- Sudden severe eye pain with redness, halos, headache and nausea (possible acute glaucoma, more common with high hyperopia)
See a doctor within a day or two
- Sudden blurred vision in one or both eyes that glasses do not fix
- A child with an eye that turns in or out, or a white or dull pupil in photos
- Pain, redness and light sensitivity in a contact lens wearer
Book a routine appointment
- Squinting, sitting close to screens, or blurred distance vision
- Headaches or eye strain after reading or screen use
- Needing to hold reading material farther away after age 40
- Frequent changes in glasses, or new distortion of lines (possible keratoconus)
Usually safe to manage at home
- Mild eye strain from long screen sessions: take regular breaks and look into the distance
How the eye focuses
Light enters through the cornea, the clear front window, which provides about two-thirds of the eye's focusing power. It then passes through the lens, which fine-tunes focus and changes shape to focus on near objects (accommodation). In a normal eye (emmetropia), light comes to a sharp point on the retina.
A refractive error happens when:
- the eyeball is too long or too short for its focusing power
- the cornea or lens is unevenly curved
- the lens loses its flexibility with age
Refractive errors are measured in diopters (D). A minus number means nearsightedness, a plus number farsightedness, and a "cylinder" value astigmatism.
Types of refractive errors
| Type | What happens | Vision | Typical onset |
|---|---|---|---|
| Myopia (nearsightedness) | Eye too long or cornea too steep; light focuses in front of the retina | Distance blurry, near clear | Childhood, often age 6 to 14; can progress into the 20s |
| Hyperopia (farsightedness) | Eye too short or cornea too flat; light focuses behind the retina | Near blurry; distance may be clear in young people who can compensate | Present from birth; often noticed later |
| Astigmatism | Cornea or lens curved more in one direction, like a rugby ball | Blurred or stretched at all distances | Often present from birth |
| Presbyopia | Lens stiffens with age and cannot focus up close | Near blurry; need to hold things farther away | Around age 40 to 45, everyone |
How common are they?
Myopia is rising rapidly worldwide, linked to more near work and less time outdoors in childhood. It is estimated that about half the world's population could be myopic by 2050. Presbyopia affects virtually everyone by their late 40s.
Symptoms
- Blurred vision at distance, near or both
- Squinting to see more clearly
- Eye strain, tired eyes, or burning after reading or screen use (eye strain)
- Headaches, especially in the forehead after visual tasks
- Difficulty driving at night, glare and halos
- In children: sitting close to the TV, holding books close, rubbing eyes, closing one eye, poor concentration in class, or avoiding reading
Many children do not realize their vision is blurry because they have never seen clearly, so screening is important.
Refractive errors in children
Uncorrected refractive errors in early childhood can stop the brain from developing normal vision in one or both eyes, causing amblyopia (lazy eye). Strong hyperopia can also cause the eyes to turn in (strabismus).
- Vision screening is recommended at well-child visits, with instrument-based screening from age 1 and chart-based testing from about age 3 to 5.
- Children who fail screening, or have a family history of strong glasses, squint or lazy eye, need a full eye exam.
- Amblyopia is most treatable before about age 7, though older children can still improve.
Slowing myopia in children
High myopia raises the lifetime risk of retinal detachment, glaucoma, cataract and myopic macular degeneration, so slowing its progression matters. Options include:
- Outdoor time: around 2 hours a day of outdoor light reduces the chance of myopia developing
- Low-dose atropine eye drops
- Myopia control spectacle lenses with special defocus designs
- Myopia control soft contact lenses, such as dual-focus daily lenses
- Orthokeratology: rigid lenses worn overnight to reshape the cornea
How refractive errors are diagnosed
An optometrist or ophthalmologist performs:
- Visual acuity test with a letter chart (20/20 means you see at 20 feet what a typical eye sees at 20 feet).
- Refraction: you compare lenses ("which is clearer, one or two?") or an automated machine measures your prescription.
- Cycloplegic refraction in children: eye drops relax focusing muscles so hidden hyperopia is not missed.
- Corneal topography if keratoconus or irregular astigmatism is suspected.
- A full eye health exam, since blurred vision can also come from cataracts, diabetes or retinal disease.
Correction options
Glasses
The simplest and safest option. Types include single-vision, bifocal and progressive lenses for presbyopia, and dedicated reading glasses.
Contact lenses
- Soft daily, two-week or monthly lenses
- Toric lenses for astigmatism
- Multifocal lenses for presbyopia
- Rigid gas-permeable and scleral lenses for high or irregular astigmatism and keratoconus
Never sleep, swim or shower in contacts unless they are approved for it, and never rinse lenses or cases in tap water, to avoid serious corneal infection.
Refractive surgery
| Procedure | How it works | Suitable for |
|---|---|---|
| LASIK | A thin corneal flap is created and the laser reshapes the tissue beneath | Myopia, hyperopia, astigmatism with adequate corneal thickness |
| PRK | The laser reshapes the corneal surface directly; slower recovery | Thinner corneas, contact sports |
| SMILE | A small lens-shaped piece of tissue is removed through a tiny incision | Myopia, astigmatism |
| Implantable collamer lens (ICL) | A lens placed in front of the natural lens | High myopia, thin corneas |
| Refractive lens exchange | Natural lens replaced with an implant | Older adults, high hyperopia, presbyopia |
Candidates should be at least 18 (usually older), have a stable prescription for at least a year, and healthy eyes. Risks include dry eye, glare and halos, and under- or over-correction.
Frequently asked questions
What are the 4 types of refractive errors?
The four types are myopia (nearsightedness, blurry distance vision), hyperopia (farsightedness, blurry near vision), astigmatism (uneven corneal curve causing blur at all distances) and presbyopia (age-related loss of near focus, starting around 40). Many people have a combination.
What causes refractive errors?
They are caused by the shape of the eye. An eye that is too long causes myopia, too short causes hyperopia, an unevenly curved cornea causes astigmatism, and a stiffening lens with age causes presbyopia. Genes play a major role, and myopia is also linked to lots of near work and little outdoor time.
Can refractive errors be cured?
Glasses and contact lenses correct vision but do not change the eye. Refractive surgery such as LASIK permanently reshapes the cornea and can eliminate the need for glasses, though presbyopia still develops with age. Myopia in children can be slowed but not reversed.
Are refractive errors hereditary?
Yes, partly. Children with one or both parents who are nearsighted have a higher chance of myopia. Astigmatism and hyperopia also run in families. Environment matters too, especially for myopia, which is more common in children who spend little time outdoors.
How often should you have an eye exam for refractive errors?
Children should have vision screening at regular checkups and a full exam if they fail or have risk factors. Adults with glasses or contacts usually need an exam every 1 to 2 years. Adults over 60, or with diabetes or glaucoma risk, need yearly exams.
Sources
This guide was written from current patient and clinical guidance, including:
- National Eye Institute: Refractive Errors
- American Academy of Ophthalmology: Refractive Errors Preferred Practice Pattern
- World Health Organization: Blindness and vision impairment fact sheet
- American Academy of Pediatrics: Visual System Assessment in Infants, Children, and Young Adults
- American Optometric Association: Myopia management