Myopia (Nearsightedness): Causes, Mechanism & Correction

Myopia is a refractive error where distant objects appear blurred while near vision remains clear. It is the most common ocular disorder globally, affecting ~30% of the world population (projected 50% by 2050).

Optical Mechanism

• Axial myopia: Eyeball too long (axial length >24 mm) → focal point anterior to retina.
• Refractive myopia: Cornea/lens too powerful (excessive curvature or index).
• Most myopia is mixed, predominantly axial.

Risk Factors

• Genetics: 2× risk if one parent myopic; 5–8× if both.
• Environment: Near work (reading, screens), low outdoor time (<2 hrs/day), low light exposure.
• Education/urbanization: Strong correlation with schooling intensity.

Classification

• Low: −0.50 to −3.00 D
• Moderate: −3.25 to −6.00 D
• High: >−6.00 D (pathologic risks: retinal detachment, glaucoma, myopic maculopathy, cataract)

Correction & Control

• Spectacles/contact lenses: Concave (minus) lenses diverge light onto retina.
• Refractive surgery (adults): LASIK, PRK, SMILE, ICL.
• Myopia control (children): Ortho‑K, low‑dose atropine (0.01–0.05%), multifocal contacts, DIMS/HAL lenses—slow axial elongation by 30–60%.
• Lifestyle: ≥2 hrs/day outdoors, 20‑20‑20 rule (every 20 min, look 20 ft for 20 sec).