Myopia

Myopia (short sightedness) is a refractive error in which distant objects appear blurred while near objects remain clear, because the eye is too long (axial myopia) or the cornea or lens is too powerful, so light focuses in front of the retina. Its prevalence is rising worldwide, affecting about 30 percent of the global population, more than 80 percent of young adults in parts of East Asia, and projected to reach 50 percent by 2050.

High myopia, usually defined as a spherical equivalent of minus 6.00 dioptres or worse, or axial length over 26 mm, carries a lifelong risk of sight threatening disease.

• Onset is usually in school years (6 to 12 years); progression is fastest in younger children (about minus 0.50 to minus 1.00 dioptre a year) and slows in the late teens.
• Risk factors: parental myopia (one parent: 2 to 3 times higher risk; both parents: 6 times), prolonged near work, low time outdoors, urban living, high educational pressure, early onset.
• Types: simple myopia, pathological (degenerative) myopia, nocturnal and pseudomyopia (accommodative spasm), secondary myopia (nuclear cataract, medications, diabetes, keratoconus, corneal ectasia).
• Complications of high myopia: myopic macular degeneration, retinal tears and detachment, posterior staphyloma, choroidal neovascularisation, open angle glaucoma, cataract (posterior subcapsular), amblyopia.

• Blurred distance vision, squinting, difficulty reading the board, sitting close to the television, headaches, eye strain, clear near vision.
• Children are often unaware; teachers or parents notice.
• Examination: reduced uncorrected distance acuity that improves with minus lenses or pinhole; normal fundus in low myopia; tilted discs, temporal conus, tessellated fundus and chorioretinal atrophy in high myopia.
• Red flags: sudden onset flashes, floaters or a curtain over the field (retinal tear or detachment), metamorphopsia or central blur (myopic choroidal neovascularisation), rapid progression, reduced vision not corrected by lenses, onset before 6 years or in adulthood (secondary causes), pain, glare.

• Visual acuity, pinhole test, cycloplegic autorefraction and subjective refraction (cyclopentolate 1 percent, 1 drop twice 5 minutes apart in children over 12 months) to exclude accommodative spasm.
• Axial length by optical biometry (monitors progression; above 26 mm is high myopia).
• Dilated fundus examination, optical coherence tomography for myopic maculopathy, intraocular pressure, visual field if glaucoma suspected.
• Corneal topography before contact lenses or surgery.
• Differentials: pseudomyopia, nuclear sclerosis, keratoconus, diabetes related refractive shifts, drug effect (sulfonamides, topiramate with acute myopia and angle closure).

• Optical correction: minus spectacles or contact lenses to full correction of distance vision.
• Myopia control in school age children (start when myopia is progressing, with a spherical equivalent of minus 0.50 dioptre or worse, or in children at high risk):
  • Low dose atropine eye drops 0.01 to 0.05 percent, 1 drop in each eye at night (0.05 percent has the best supported effect, slowing progression by about 40 to 60 percent over 2 years; side effects are mild photophobia and near blur, managed with photochromic or progressive lenses); continue for at least 2 to 3 years and taper gradually to avoid rebound.
  • Orthokeratology (overnight rigid contact lenses that reshape the cornea) and daily disposable dual focus soft contact lenses.
  • Spectacle lenses with defocus technology (multi segment or lenslet designs).
  • Outdoor time of at least 2 hours a day (reduces onset by about 25 to 50 percent), breaks from near work, reading distance over 30 cm, good lighting.
• Adults: spectacles, contact lenses, or refractive surgery once stable (LASIK, PRK, SMILE; implantable collamer lens for high myopia or thin corneas).
• Follow up every 6 months in children (refraction and axial length), annually in adults; dilated fundus examination every 1 to 2 years in high myopia.
• Educate on warning signs of retinal detachment (new flashes, floaters, shadow): seek same day assessment.
• Avoid contact sports with head impact in high myopia without advice; reduce smoking.
• Refer for high or rapidly progressive myopia, retinal lesions, or suspected secondary cause.