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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

Myopia

Walter Huang, OD

Yuanpei University

Department of Optometry

definition
Definition
  • The common name for this refractive error is near-sightedness
  • Patients with myopia are known as myopes
definition3
Definition
  • When parallel rays of light enter the eye (with accommodation relaxed) and come to a single point focus in front of the retina
etiology
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
etiology5
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)
prevalence
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%
prevalence7
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%
prevalence8
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
prevalence9
Prevalence
  • Ethnicity
    • Higher prevalence in Asians, Arabs, and Jews
    • Lower prevalence in Caucasians, Blacks, and South Sea Islanders
prevalence10
Prevalence
  • Urban versus rural communities
    • Myopia is more common in urban communities than in rural ones
progression
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
juvenile onset myopia
Juvenile-Onset Myopia
  • Definition
    • Myopia in which the age of onset is 8 to 12 years
juvenile onset myopia13
Juvenile-Onset Myopia
  • Etiology
    • Evidence for genetics influences
      • Greater similarity of refractive error and ocular structures in identical twins than in fraternal twins
juvenile onset myopia14
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
juvenile onset myopia15
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
symptoms
Symptoms
  • Blurry vision at distance
  • Clear vision at near
  • Squinting
  • Occasional headaches
signs
Signs

Decreased visual acuities at distance

clinical tests
Clinical Tests
  • Visual acuity tests - distance
  • Retinoscopy
  • Subjective refraction
management
Management
  • Divergent or minus lenses in spectacles or contact lenses
  • Cycloplegics
  • Surgery
  • Refractive surgery
management21
Management
  • Spectacles
    • Single vision glasses
    • Bifocal glasses
      • More effective in children with near esophoria
management22
Management
  • Contact lenses
    • Soft contact lenses
    • Rigid gas permeable contact lenses
    • Ortho-keratology contact lenses
    • Corneal reshaping therapy contact lenses
management23
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
management24
Management
  • Cycloplegics (e.g., atropine)
    • Reduce the ability to accommodate
    • May slow the progression of myopia
management25
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
management26
Management
  • Surgery
    • Radial keratotomy (RK)
      • Post-surgical complications
        • Hyperopic shift
        • Diurnal fluctuations of refractive error and visual acuity
        • Glare
        • Corneal scarring
management27
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
management28
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
management29
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
management30
Management
  • Refractive surgery
    • Laser in-situ keratomileusis (LASIK)
      • Post-surgical complications
        • Severe dry eye syndrome
        • Poor night vision
        • Reduced contrast sensitivity
        • Astigmatism
management31
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
pathological conditions associated with myopia
Pathological Conditions Associated with Myopia
  • Cataract
    • Nuclear cataract causes a myopic shift
pathological conditions associated with myopia33
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
pathological conditions associated with myopia34
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