What is myopia (nearsightedness), its causes, symptoms, and treatment options, particularly in school-aged children and young adults?

Myopia: Comprehensive Overview

Definition

Myopia (nearsightedness) is a refractive error where parallel rays of light from distant objects focus anterior to the retina rather than directly on it, resulting in blurred distance vision while near objects remain clear 1. Low to moderate myopia is defined as less than 6.00 diopters (D) of spherical equivalent, while high myopia is 6.00 D or more 1.

Epidemiology and Prevalence

United States Population

• The prevalence of myopia in U.S. children aged 5-17 years is approximately 9%, with significant variation by ethnicity 1.
• In very young children (6-72 months), prevalence varies: 1.2% in non-Hispanic white children, 4.0% in Asian children, 6.6% in African American children, and 3.7% in Hispanic children 1.
• Among adults aged 40 and older, myopia affects 25-31% of the population, with higher rates (35-40%) in those aged 20-40 years 1.
• Over 93 million Americans aged 12 and older use eyewear to correct refractive errors 1.

Global Trends

• Myopia prevalence is rapidly increasing worldwide, reaching epidemic proportions in East Asia where 80-90% of school-aged children are now affected 1, 2.
• In Taiwan, prevalence increased from 12% in 6-year-olds to 84% in 16-18-year-olds 1.
• Studies show the prevalence has doubled in Finland over the 20th century and increased markedly in Israel, Australia, India, and Japan 1.

Risk Factors and Causes

Environmental Factors

• Reduced outdoor time is the most significant modifiable risk factor; children with little daylight exposure have a 5-fold increased risk of myopia, rising to 16-fold when combined with extensive near work 3.
• Multiple studies demonstrate that increased outdoor time (particularly in early childhood) is protective against myopia development 1, 4.
• Higher levels of formal education are strongly associated with increased myopia prevalence 1.
• The relationship between near work and myopia is less clear than previously believed, with recent evidence showing weaker associations than outdoor time 1.

Genetic Factors

• Both hereditary and environmental factors contribute to myopia development 1.
• Studies show higher concordance between monozygotic twins than dizygotic twins 1.
• Several gene regions, particularly chromosome 18p, have been linked to myopia 1.
• Parental myopia increases risk in children 1.

Demographic Patterns

• Myopia is more prevalent in non-Hispanic white adults compared to non-Hispanic black or Mexican American populations in the U.S. 1.
• Asian populations show significantly higher prevalence rates across all age groups 1.

Clinical Presentation and Symptoms

Visual Symptoms

• Blurred distance vision while near vision remains clear 1, 2.
• Difficulty with activities requiring distance vision such as driving, watching television, or seeing the classroom board 1.
• Some patients experience increased myopia at low illumination levels (night myopia) requiring stronger correction for nighttime activities 1.

Progressive Nature

• Myopia typically progresses during childhood and adolescence, necessitating screening examinations with visual acuity testing every 1-2 years 1.
• Progression tends to be slower during summer months compared to other seasons 1.

Associated Complications

Patients with high refractive errors face potentially increased incidence of associated pathologic conditions 1. These include:

• Retinal detachment 2
• Glaucoma 2
• Cataract 2
• Myopic maculopathy 1

Treatment and Management Options

Optical Correction

Eyeglasses

• Individuals with low myopia may not require constant eyeglass correction except for specific distance activities 1.
• Overcorrection should be avoided as it causes excessive accommodation and may create symptoms 1.
• Full correction is appropriate for most patients, with adjustments for night myopia when needed 1.

Contact Lenses

• Approximately 41 million Americans use contact lenses 1.
• Daily disposable contact lenses are the safest option with the lowest complication rates compared to planned replacement lenses 1.
• Overnight wear of any contact lens type significantly increases the risk of microbial keratitis and should be avoided 1.
• Hydrogen peroxide disinfection systems are superior to multipurpose solutions for reducing infection risk 1.

Myopia Prevention Strategies

Increased Outdoor Time

• School-based interventions to increase outdoor time show moderate-certainty evidence for reducing myopia incidence and progression 4.
• At 2 years, interventions reduced myopia incidence by 4.2% (22.5% vs 26.7%) and slowed refractive error progression by 0.13 D 4.
• At 3 years, myopia incidence was reduced by 9.3% (30.5% vs 39.8%) 4.
• The American Academy of Ophthalmology recommends considering increased outdoor time for myopia prevention in young children at risk 1.

Low-Dose Atropine

• Low-dose atropine and increased outdoor time have been shown to reduce the likelihood of myopia onset 1.
• The American Academy of Ophthalmology recommends considering low-dose atropine for myopia prevention in young children at risk 1.

Myopia Control in School-Age Children

Antimuscarinic Agents (Atropine)

• Atropine eye drops are highly effective, reducing myopic progression by 1.00 D at one year compared to placebo (moderate-certainty evidence) 5.
• Axial elongation was reduced by 0.35 mm with atropine treatment 5.
• Two meta-analyses and a large Asian randomized trial demonstrated that atropine can reduce myopia progression by up to 0.71 D over two years at concentrations with minimal side effects 3.
• Higher doses may cause rebound progression after cessation 3.
• The American Academy of Ophthalmology recommends considering antimuscarinic agents for myopia control in school-age children 1.
• Common side effects include accommodation difficulties (RR 9.05) and papillae/follicles (RR 3.22) 5.

Multifocal Optical Corrections

• Multifocal spectacles or contact lenses provide small but significant benefits, reducing progression by 0.14 D compared to single vision lenses (moderate-certainty evidence) 5.
• Axial elongation was reduced by 0.06 mm with multifocal lenses 5.
• Bifocal soft contact lenses reduced axial elongation by 0.11 mm (low-certainty evidence) 5.
• The American Academy of Ophthalmology recommends considering multifocal spectacles or contact lenses for myopia control in school-age children 1.

Orthokeratology

• Orthokeratology contact lenses were more effective than single vision lenses in slowing axial elongation by 0.28 mm (moderate-certainty evidence) 5.
• The American Academy of Ophthalmology recommends considering orthokeratology for myopia control in school-age children 1.

Combination Therapy

• Atropine plus multifocal spectacles reduced progression by 0.78 D compared to placebo plus single vision lenses (moderate-certainty evidence) 5.
• Axial elongation was reduced by 0.37 mm with combination therapy 5.

Other Pharmacological Agents

• Pirenzepine gel reduced progression by 0.31 D at one year (moderate-certainty evidence) 5.
• Cyclopentolate showed benefit of 0.34 D (moderate-certainty evidence) 5.
• Systemic 7-methylxanthine and timolol eye drops showed little to no effect 5.

Refractive Surgery

• Over 8.5 million Americans have undergone keratorefractive surgery since 1995 1.
• More than 13 million LASIK procedures have been performed in the United States 1.
• Surgery is appropriate for correcting symptomatic refractive errors as desired by the patient and deemed appropriate by the physician 1.

Clinical Management Algorithm

Initial Assessment

• Determine patient's visual needs and quantify refractive error 1.
• Identify high-risk patients (family history, ethnicity, limited outdoor time, high educational demands) 1, 3.

Prevention (Young Children at Risk)

1. Increase outdoor time to at least 2 hours daily 1, 4
2. Consider low-dose atropine for high-risk children 1

Myopia Control (School-Age Children with Progression)

1. First-line: Low-dose atropine (0.01-0.05%) - strongest evidence for efficacy 3, 5
2. Second-line: Orthokeratology or multifocal contact lenses 1, 5
3. Alternative: Multifocal spectacles (smaller effect but non-invasive) 1, 5
4. Consider combination therapy (atropine + multifocal correction) for rapid progressors 5

Optical Correction

• Low myopia: Prescribe glasses for distance activities only 1
• Moderate to high myopia: Full-time correction recommended 1
• Contact lens wearers: Prioritize daily disposable lenses with hydrogen peroxide disinfection 1
• Eliminate overnight wear to reduce infection risk 1

Monitoring

• Screen children every 1-2 years during growth period 1
• Monitor for complications in high myopia (≥6.00 D) 1
• Assess compliance with myopia control interventions 5

Important Clinical Considerations

Safety Concerns

• No serious adverse events were reported across myopia control interventions 5, 4.
• Antimuscarinic medications cause predictable accommodation difficulties and conjunctival changes 5.
• Contact lens-related infections remain a significant concern despite newer lens technologies 1.

Lifestyle Modifications

• Promoting outdoor activities is essential and has no adverse effects 1, 4.
• Balanced nutrition may play a role, though evidence is still emerging 6.
• Physical activity should be encouraged as part of overall health promotion 6.