10 Types of Myopia: Classification and Clinical Significance
Myopia is a refractive error characterized by parallel light rays focusing in front of the retina, resulting in blurry distance vision. There are 10 distinct types of myopia that can be classified based on clinical presentation, age of onset, progression pattern, and underlying pathophysiology.
Primary Classifications of Myopia
1. Simple/Physiological Myopia
- Characterized by refractive error between -0.50D and -6.00D 1
- Typically develops between ages 6-12 years
- Progresses at approximately 0.50D per year 2
- No pathological ocular changes
- Most common form of myopia in the general population
2. High/Pathological Myopia
- Defined as spherical equivalent refractive error ≤-6.00D 3
- Associated with significant ocular pathology
- Higher risk of complications including:
3. Axial Myopia
- Results from excessive elongation of the eyeball
- Most common anatomical cause of myopia
- Strongly associated with pathological changes when severe
- Each millimeter of axial length increase corresponds to approximately 3D of myopia 3
4. Refractive Myopia
- Results from increased refractive power of the optical components (cornea, lens)
- Normal axial length
- Less commonly associated with pathological changes
- May be due to increased corneal curvature or lens changes 1, 3
Classification by Age of Onset
5. Congenital Myopia
- Present at birth or early infancy
- Often high in magnitude
- May be associated with other ocular or systemic abnormalities
- Usually non-progressive or slowly progressive 5
6. Youth-Onset Myopia
- Develops between 6-12 years of age
- Most common form of myopia
- Progressive until early adulthood
- Strongly influenced by both genetic and environmental factors 5, 6
7. Early Adult-Onset Myopia
- Develops between 20-40 years of age
- Often associated with intensive near work
- Generally lower magnitude than youth-onset myopia
- Typically stabilizes after a few years 5
8. Late Adult-Onset Myopia
- Develops after age 40
- May be related to early nuclear sclerotic cataracts
- Often transient or slowly progressive
- Less influenced by genetic factors 5
Special Types
9. Secondary Myopia
- Results from other ocular or systemic conditions or medications
- Causes include:
- Diabetes (transient glucose-induced changes)
- Cataracts
- Medications (e.g., sulfonamides, tetracyclines)
- Keratoconus
- May be reversible when underlying cause is addressed 3
10. Nocturnal/Night Myopia
- Increased myopia in low light conditions
- Typically 0.50D to 1.00D more myopic than daytime vision
- Due to increased spherical aberration and accommodation in dim light
- May require specific correction for night driving 1
Clinical Management Considerations
- Screening for myopia should be part of routine pediatric eye examinations
- Patients with high myopia require regular monitoring for complications
- Myopia control strategies should be considered for progressive myopia in children:
Risk Factors and Prevention
- Genetic factors: Asian ethnicity, parental myopia
- Environmental factors: excessive near work, limited outdoor time
- Preventive measures:
Understanding these different types of myopia is essential for appropriate clinical management, prevention strategies, and patient education about potential complications and treatment options.