Pathophysiology of Myopia
Myopia (nearsightedness) develops primarily due to excessive axial elongation of the eyeball, resulting from complex gene-environment interactions that disrupt normal eye growth regulation. 1, 2
Key Pathophysiological Mechanisms
Anatomical Changes
- Axial elongation: The primary structural change in myopia is an abnormal increase in the eye's axial length 3
- This elongation causes light rays to focus in front of the retina rather than directly on it
- The degree of myopia correlates with the extent of axial elongation
Genetic Factors
- More than 450 common genetic loci have been identified in association with myopia 1
- Higher prevalence observed in children whose parents are myopic, suggesting strong genetic predisposition 3
- Genetic factors influence:
- Eye growth regulation
- Scleral remodeling
- Response to environmental triggers
Environmental Triggers
- Near work activities: Prolonged reading, screen time, and close-up tasks are strongly associated with myopia development 1, 4
- Limited outdoor exposure: Reduced time outdoors is a significant risk factor 4
- Educational intensity: Higher levels of education and academic pressure correlate with increased myopia prevalence 1
Gene-Environment Interactions
- Genetic susceptibility combined with environmental triggers accelerates myopia development 1
- Specific genetic loci have been found to interact with near work and educational level 1
- This interaction explains the rapid increase in myopia prevalence in industrialized countries that cannot be attributed to genetics alone 3
Optical Defocus Mechanism
- Prolonged near work creates peripheral hyperopic defocus on the retina
- This defocus triggers compensatory eye growth signals
- The eye elongates in an attempt to move the focal plane back to the retina
- This compensatory mechanism becomes dysregulated, resulting in progressive myopia 3, 2
Progression and Complications
- Early onset myopia typically progresses more rapidly 4
- High myopia (≥-6 diopters) affects approximately 20% of myopic individuals 4
- Pathological changes associated with severe myopia include:
Clinical Implications
- Hyperopia ≤0.5 diopters in children is a predictor of future myopia development 4
- Myopia is now considered not just a refractive error but an eyesight-threatening disease 4
- It represents the sixth leading cause of blindness globally 3
- Prevention strategies focus on:
Important Considerations
- The global prevalence of myopia is increasing dramatically, reaching 80-90% in young adults in East Asia 4
- This rapid increase suggests environmental factors are becoming increasingly influential 3
- Understanding the pathophysiology is crucial for developing effective interventions to delay onset and slow progression 2