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Myopia

Myopia. Walter Huang, OD Yuanpei University Department of Optometry. Definition. The common name for this refractive error is near-sightedness Patients with myopia are known as myopes. Definition.

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Myopia

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  1. Myopia Walter Huang, OD Yuanpei University Department of Optometry

  2. Definition • The common name for this refractive error is near-sightedness • Patients with myopia are known as myopes

  3. Definition • When parallel rays of light enter the eye (with accommodation relaxed) and come to a single point focus in front of the retina

  4. Etiology • Axial length • The axial length of the eye is longer than normal due to imperfect emmetropization • The most common cause of myopia for high myopes

  5. Etiology • Refractive power • The refractive power of the eye is too strong • Curvature myopia • Cornea or lens has a steep curvature (e.g., keratoconus) • Increased index of refraction (e.g., cornea, lens) • Anterior movement of the lens (e.g., nuclear sclerosis)

  6. Prevalence • Age • At birth: 24 to 50% • As birth weight decreases, the amount of myopia increases in premature infants • The mean refractive error for full-term infants is +2.00 D • The prevalence of myopia decreases by 1 year old due to the process of emmetropization • 5 to 6 years old: 2% (>-0.50DS) • 13 to 14 years old: 15%

  7. Prevalence • Age • In Taiwan (1995) • 7 years old: 12% • 12 years old: 56% • 15 years old: 76% • 18 years old: 84% • In western countries • 20 years old: 20%

  8. Prevalence • Gender • In general, there are no significant differences between males and females • Progression of myopia tends to begin and end earlier in females • High myopia is more common in females

  9. Prevalence • Ethnicity • Higher prevalence in Asians, Arabs, and Jews • Lower prevalence in Caucasians, Blacks, and South Sea Islanders

  10. Prevalence • Urban versus rural communities • Myopia is more common in urban communities than in rural ones

  11. Progression • Myopia tends to increase linearly until the middle or late teenage years, at which point, it levels off • The earlier a child becomes myopic, the more rapidly the condition tends to progress

  12. Juvenile-Onset Myopia • Definition • Myopia in which the age of onset is 8 to 12 years

  13. Juvenile-Onset Myopia • Etiology • Evidence for genetics influences • Greater similarity of refractive error and ocular structures in identical twins than in fraternal twins

  14. Juvenile-Onset Myopia • Etiology • Evidence for genetics influences • Increased prevalence of myopia in children of myopic parents • Probability of a child being myopic is: • 40% when both parents are myopic • 20 to 30% when one parent is myopic • <10% when neither parent is myopic

  15. Juvenile-Onset Myopia • Etiology • Evidence for environmental influences • Association between near work, education, and myopia • Children who do a lot of near work, like reading, tend to become myopic • Myopia is more common where occupations require extensive near work

  16. Myopia and Visual Acuity

  17. Symptoms • Blurry vision at distance • Clear vision at near • Squinting • Occasional headaches

  18. Signs Decreased visual acuities at distance

  19. Clinical Tests • Visual acuity tests - distance • Retinoscopy • Subjective refraction

  20. Management • Divergent or minus lenses in spectacles or contact lenses • Cycloplegics • Surgery • Refractive surgery

  21. Management • Spectacles • Single vision glasses • Bifocal glasses • More effective in children with near esophoria

  22. Management • Contact lenses • Soft contact lenses • Rigid gas permeable contact lenses • Ortho-keratology contact lenses • Corneal reshaping therapy contact lenses

  23. Management • Contact lenses • Ortho-keratology • Rigid gas permeable contact lenses are used to flatten the cornea • Results are unpredictable (0 to 5.00 D of change) • Two eyes may respond differently in anisometropia • Procedure may induce astigmatism • Retainer lens is required; otherwise, the patient’s prescription may return to normal

  24. Management • Cycloplegics (e.g., atropine) • Reduce the ability to accommodate • May slow the progression of myopia

  25. Management • Surgery • Radial keratotomy (RK) • Technique • Eight cuts with a blade in a radial pattern are made on the surface of the cornea • The depth of each cut is through approximately 85 to 90% of the cornea

  26. Management • Surgery • Radial keratotomy (RK) • Post-surgical complications • Hyperopic shift • Diurnal fluctuations of refractive error and visual acuity • Glare • Corneal scarring

  27. Management • Refractive surgery • Photorefractive keratectomy (PRK) • Technique • High energy photons from an excimer laser are used to photoablate a small amount of tissue from the anterior corneal surface and sculpt the cornea

  28. Management • Refractive surgery • Photorefractive keratectomy (PRK) • Post-surgical complications • Eye pain • Corneal disruption • Blurry vision • Prolonged duration of drug use • Greater time needed for eyesight recovery

  29. Management • Refractive surgery • Laser in-situ keratomileusis (LASIK) • Technique • A microkeratome is used to cut a flap of superficial corneal tissue • The flap is lifted back, exposing the underlying corneal stroma • The excimer laser is used to perform tissue removal in the corneal stroma • The flap is repositioned in its original position and adheres to the underlying corneal stroma without the need for sutures

  30. Management • Refractive surgery • Laser in-situ keratomileusis (LASIK) • Post-surgical complications • Severe dry eye syndrome • Poor night vision • Reduced contrast sensitivity • Astigmatism

  31. Management • Refractive surgery • Points to consider after the surgical procedure • Use eyedrops, as prescribed by the ophthalmologist • Be careful not to allow chlorinated water , shampoo, and sweat to come into contact with the eyes • Wear sunglasses when outside to protect the eyes from sunlight • Remember to go back to the hospital for regular follow up visits with the ophthalmologist and to get eyedrops

  32. Pathological Conditions Associated with Myopia • Cataract • Nuclear cataract causes a myopic shift

  33. Pathological Conditions Associated with Myopia • Diabetes • High blood glucose levels cause increased sorbital levels in the lens • Water rushes in and dilutes the sorbital in the lens • Lens bulges and results in a myopic shift

  34. Pathological Conditions Associated with Myopia • Marfan’s syndrome • Suspensory ligaments break • Subluxation of lens occurs superiorly and temporally and results in a very high increase in myopia

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