Refractive errors

Refractive errors (ametropia) are conditions in which light rays entering the eye are not focused on the retina, leading to blurred vision. Abnormalities in eye anatomy affecting the refractory media (e.g., axial eye length, corneal curvature) lead to myopia, hyperopia, astigmatism, and/or presbyopia. Visual acuity testing is used to detect refractive errors; diagnosis and severity are determined by refraction testing as part of a comprehensive eye examination. Treatment typically involves corrective lenses (glasses, contact lenses) or refractive surgery. Individuals with refractive errors, particularly those with a high myopic error, are at increased risk for other eye conditions (e.g., retinal detachment, glaucoma, cataracts). Routine visual acuity testing is recommended for children and adolescents; screening recommendations for adults vary.

Myopia ^[1]

• A refractive error in which light rays entering the eye are focused anterior to the retina
• Increased axial length of the eye or, less commonly, increased refraction → focal point anterior to the retina
• Nearby objects appear in focus, while objects in the distance appear blurry.

Hyperopia ^[1]

• A refractive error in which light rays entering the eye are focused posterior to the retina
• Decreased axial length of the eye → focal point posterior to the retina
• Nearby objects appear blurry, while objects in the distance appear in focus.

Presbyopia ^[1]

• An age-related decrease in the power of accommodation of the eye
• ↓ Lens elasticity, ↓ strength of ciliary muscle, and ↓ lens curvature → ↓ lens accommodation (focusing on an object up close)
• Typically leads to the inability to focus on nearby objects.

Astigmatism ^[1]

• A refractive error in which abnormal curvature of the cornea leads to two or more focal points, causing blurred vision at all distances
• Abnormal curvature of the cornea → distorted refraction → two or more focal points, which can be anterior and/or posterior to the retina, depending on the curvature

Individuals with refractive errors who develop cataracts may experience a temporary improvement in vision (second sight) due to the change in the refractive index of the lens.

Increased time spent outdoors, low-dose topical atropine, multifocal lenses, and orthokeratology can slow progression mild to moderate myopia in children and adolescents. ^[1]
Individuals with high refractive errors (≥ 6 diopters of myopia, ≥ 3 diopters of hyperopia, or ≥ 3 diopters of regular astigmatism) are at increased risk for complications and other ocular conditions compared to individuals with less severe refractive errors. ^[1]

• Blurred vision: See “Overview of refractive errors” for features specific to the type of refractive error.
• Diplopia ^[3]
• Asthenopia: symptoms associated with overuse of the eyes ^[3]
  • Eye pain
  • Lacrimation
  • Burning or itching eyes
• Headache associated with refractive errors ^[4]
  • Aggravated by visual tasks at distances at which vision is impaired and alleviated upon task cessation
  • Chronic; usually daily
  • Typically worse in the second half of the day
  • Improves significantly after correction of refractive error(s)

• Assess visual acuity for near and distant vision.
• Refer to ophthalmology or optometry for refraction testing, a comprehensive eye examination, and further management.
• Use shared decision-making to determine management; options include:
  • Expectant management
  • Corrective lenses
  • Refractive surgery
  • Daily topical pilocarpine (for presbyopia only)
• For children with myopia, discuss strategies to slow progression such as: ^[1][5]
  • Increased time spent outdoors
  • Low-dose atropine eye drops
  • Multifocal lenses
  • Orthokeratology
• Follow up ^[1]
  • Patients who use corrective lenses: Annually until refraction is stable; then every 1–2 years.
  • Patients who have undergone refractive surgery: As recommended by the treating ophthalmologist.

Correction of low or monocular refractive errors in asymptomatic patients is not necessary. ^[1]

Topical pilocarpine use is associated with an increased risk of retinal detachment and retinal tears. Perform a dilated fundoscopic examination in all patients before prescribing pilocarpine for presbyopia. ^[1]

• Glasses and contact lenses help focus light rays entering the eye on the retina.
• Multifocal (e.g., bifocal, trifocal, or progressive) lenses correct visual acuity at multiple distances.
• The modality used is typically based on patient preference.

Glasses ^[1]

Indications

• First-line treatment for refractive errors
• Contraindications to contact lenses
• Need or desire for eye protection
• Contact lens wearers: to prevent overuse of contact lenses

Types

• Convex, concave, or cylindrical lenses are used depending on the type of refractive error.
• See “Overview of refractive errors” for specific details.

Contact lenses ^[1]

Indications

• Refractive error
• Need or desire to decrease use of glasses
• Inadequate vision improvement with glasses
• Myopia treated with orthokeratology
• Keratoconus ^[6]
• Aphakia ^[7]

Individuals who use contact lenses should also have a pair of glasses to prevent contact lens overuse. ^[1]

Relative contraindications

• Conjunctivitis (e.g., keratoconjunctivitis sicca, blepharoconjunctivitis)
• Corneal exposure (e.g., due to incomplete eyelid closure)
• Corneal abnormalities (e.g., keratitis)
• Ocular rosacea
• Use of topical ophthalmologic steroids

Types

• Soft (e.g., soft hydrogel, silicone hydrogel) or rigid gas permeable
• Disposable (discarded daily, weekly, or monthly) or conventional lenses (replaced at least annually)

Most lenses are worn while awake and removed for sleeping; extended-wear contact lenses can be worn continuously for up to 30 days. The FDA recommends removing extended-wear contact lenses at least once a week for cleaning and disinfection.

Contact lens hygiene

Counsel all patients on the following recommendations. ^[1][8]

• Wash hands with soap and water before handling lenses.
• Do not wear contact lenses while sleeping unless prescribed (e.g., for orthokeratology).
• Avoid contact of lenses with water.
• Clean and store lenses with disinfecting contact lens solution; not water.
• Discard the used solution completely before refilling the storage case.
• Replace contact lenses and storage cases as directed.

Risk of infection is reduced by using daily disposable contact lenses and increased if contact lenses are worn while sleeping (e.g., extended-wear lenses or daily lenses left in overnight). ^[1]

Acanthamoeba, which causes Acanthamoeba keratitis, is commonly found in tap water and other water sources. Recommend removal of lenses before swimming or showering. ^[1]

Complications

• Microbial keratitis
• Corneal ulcer, neovascularization, thinning
• Giant papillary conjunctivitis

Refractive surgeries are elective ophthalmologic procedures to correct refractive errors. Indications vary by procedure; refer to ophthalmology. ^[9]

Options ^[9]

There are several types of refractive surgery. The most common options are described below.

Keratorefractive surgery

Keratorefractory surgery reshapes the cornea to focus light on the retina. Options include: ^[9][10]

• Laser-assisted in situ keratomileusis (LASIK)
  • Elevation of a flap of corneal epithelium and laser removal of a very small amount of underlying corneal stroma
  • Most commonly performed keratorefractive surgery
• Photorefractive keratectomy (PRK): laser removal of the corneal stroma
• Small incision lenticule extraction (SMILE): laser removal of a small disc of corneal tissue (a lenticule) through an incision adjacent to the cornea

Intraocular lens implantation

• Phakic intraocular lens implantation
• Refractive lens exchange

Contraindications ^[9][10]

• Unstable refractive error
• Refractive error outside the surgical range ^[10]
• Corneal abnormalities (e.g., thinning, keratoconus, Fuchs dystrophy)
• Uncontrolled ocular or systemic conditions, such as:
  • Glaucoma, dry eye disease, blepharitis, or atopy
  • Diabetes mellitus
  • Autoimmune disease (e.g., sicca syndrome)
  • Mental illness
• History of uveitis or herpetic keratitis
• Abnormal wound healing
• Concomitant use of certain medications
• Unrealistic patient expectations

Complications ^[9]

• Unwanted changes in vision (e.g., halos, glare, undercorrection, overcorrection, astigmatism)
• Dry eye ^[10]
• Corneal ectasia, corneal neuralgia
• Corrective lenses for reading and/or in low light may be needed earlier than for individuals who do not have keratorefractive surgery. ^[10]
• LASIK and PRK: corneal infiltrates, scarring, ulceration
• Intraocular lens implantation: cataract, loss of accommodation, irregular pupil, retinal detachment

Primary prevention

• Myopia ^[1]
  • Increased time outside in childhood and adolescence
  • Low-dose topical atropine
• Other refractive errors: no known preventive strategies

Screening for refractive errors

The following is applicable to individuals with no risk factors for eye diseases.

• Children ^[11]
  • Instrument-based refraction testing (e.g., with an autorefractor): 1–3 years of age
  • Visual acuity testing: starting at 3 years of age and performed at regularly scheduled intervals ^[12][13]
  • See “Pediatric vision screening.”
• Adolescents: visual acuity testing at 12 and 15 years of age ^[14]
• Adults: Recommendations vary.
  • There is insufficient evidence to recommend routine visual acuity screening in adults. ^[15]
  • Consider a comprehensive eye exam: ^[1][16][17]
    • Every 5–10 years for individuals < 40 years of age
    • Every 2–4 years for individuals 40–54 years of age
    • Every 1–3 years for individuals 55–65 years of age
    • Every 1–2 years for individuals ≥ 65 years of age

All states require visual acuity testing to acquire a driver's license; in most states, corrected visual acuity of 20/40 is required for unrestricted, noncommercial licensure. ^[18]