Pathophysiology of Myopia
Myopia develops primarily through excessive axial elongation of the eyeball, resulting from a complex interplay between genetic predisposition and environmental factors, with near work activities and limited outdoor time being key environmental triggers for this abnormal eye growth. 1, 2
Anatomical Changes
- Axial elongation: The fundamental structural change in myopia is an increase in the axial length of the eyeball 3
- This elongation causes light rays to focus in front of the retina rather than directly on it, resulting in blurred distance vision
- The severity of myopia correlates with the degree of axial elongation
Etiology: Gene-Environment Interaction
Genetic Factors
- More than 450 common genetic loci have been associated with myopia development 1
- Higher prevalence in individuals with myopic parents, strongly suggesting genetic predisposition 4
- Genetic factors influence susceptibility to environmental triggers
Environmental Factors
- Near work activities: Extended periods of close-up visual tasks (reading, screen time) 1
- Limited outdoor time: Reduced exposure to natural light 1, 5
- Educational intensity: Higher levels of education correlate with increased myopia prevalence 1
Interaction Mechanism
- Environmental factors like near work create optical blur that triggers signaling cascades
- These signals influence eye growth and remodeling in genetically susceptible individuals
- Early onset of myopia is associated with faster progression and higher risk of severe myopia 5
Progression Factors
- Age of onset: Earlier onset correlates with faster progression and higher final myopia 5
- Hyperopia ≤0.5 diopters in children is a predictor of future myopia development 5
- Educational intensity: Higher educational demands increase progression rates
- Screen time: Increased digital device use contributes to progression
Pathological Consequences
High myopia (≥-6 diopters) can lead to sight-threatening complications:
- Retinal detachment
- Choroidal neovascularization
- Early cataracts
- Glaucoma
- Macular atrophy 5
Epidemiological Significance
- Reaching epidemic proportions globally, especially in East Asia (80-90% prevalence) 5, 2
- Approximately 20% of myopic individuals develop high myopia with risk of complications 5
- Ranked as the sixth leading cause of blindness globally 4
- The rapid increase in prevalence cannot be explained by genetics alone, highlighting the critical role of environmental factors 4
Prevention and Management Implications
The understanding of myopia pathophysiology has led to effective interventions:
- Increased outdoor activity to delay onset 5
- Reduction in prolonged near work 5
- Optical interventions (defocusing lenses, orthokeratology) 2, 3
- Pharmacological approaches (low-dose atropine) 3
Understanding the pathophysiological mechanisms of myopia is crucial for developing effective strategies to prevent its onset, slow its progression, and reduce the risk of vision-threatening complications.