Pathophysiology of Myopia
Myopia develops primarily through excessive axial elongation of the eyeball due to a complex interplay between genetic predisposition and environmental factors, with near work activities and reduced outdoor time being the most significant environmental contributors. 1
Anatomical Changes in Myopia
Myopia occurs when:
- The eyeball becomes too long in the axial direction
- Light rays focus in front of the retina instead of directly on it
- This results in blurred distance vision while near objects remain clear
The primary structural changes include:
- Increased axial length of the eyeball
- Thinning of the sclera and choroid
- Stretching of the retina, particularly in high myopia
Genetic Factors
Genetic predisposition plays a significant role in myopia development:
- More than 450 common genetic loci have been identified in association with myopia 1
- Higher prevalence in children whose both parents are myopic 2
- Genetic factors influence eye growth, scleral remodeling, and response to environmental triggers
- Certain genetic variants interact with environmental factors like near work and educational level 1
Environmental Factors
Environmental influences have driven the rapid increase in myopia prevalence globally:
- Near work activities (reading, screen time, studying) increase exposure to optical blur 2
- Reduced outdoor time is strongly associated with myopia development 3
- Educational intensity correlates with myopia prevalence (explaining the 80-90% prevalence in young adults in East Asia) 3
- Urban environments with limited natural light exposure increase risk
Pathophysiologic Mechanisms
The development of myopia involves several key mechanisms:
- Defocus-driven eye growth: Peripheral retinal defocus signals trigger axial elongation
- Altered emmetropization: The natural process that regulates eye growth becomes dysregulated
- Biomechanical changes: Weakening of scleral tissue allows for progressive elongation
- Biochemical pathways: Changes in neurotransmitters (particularly dopamine) and growth factors that regulate eye growth
- Inflammation and oxidative stress may contribute to scleral remodeling
Gene-Environment Interactions
The rapid increase in myopia prevalence cannot be explained by genetics alone:
- Specific genetic variants modify the impact of environmental exposures 1
- Some individuals are genetically more susceptible to environmental triggers like near work
- These interactions provide more accurate risk prediction models 1
- Earlier onset of myopia (often school-related) leads to faster progression and greater risk of high myopia later in life 3
Progression to High Myopia
Approximately 20% of myopic individuals develop high myopia (≥-6 diopters) 3, which can lead to:
- Retinal detachment
- Choroidal neovascularization
- Early cataracts
- Glaucoma
- Macular atrophy
Risk Factors and Predictors
Several factors predict myopia development:
- Hyperopia ≤0.5 diopters in childhood is a predictor of future myopia 3
- Family history of myopia
- Reduced outdoor time during childhood
- Intensive near work activities
- East Asian ethnicity (highest prevalence globally) 4
Clinical Implications
Understanding the pathophysiology of myopia has led to several intervention strategies:
- Increased outdoor activity to delay onset 3
- Reduction in prolonged near work
- Optical interventions like defocusing lenses and orthokeratology to slow progression 5
- Pharmacological treatments such as low-dose atropine 5
The pathophysiology of myopia represents a complex interplay between genetic susceptibility and environmental triggers, with axial elongation as the primary structural change. This understanding is crucial as myopia has become a global public health concern with significant vision-threatening complications.