PEC LESSON 1

• Refractive status


  Relationship between posterior principal focus, the eye's refractive mechanism and the retina of the same eye with accommodation relaxed
• Refractive mechanisms


  • Cornea
  • Aqueous humor
  • Crystalline lens
  • Vitreous humor
• Posterior principal focus


  Focal points of the refracting mechanisms
• Retina


  Image plane in the eye which represents the extension of the brain, location of the eye that receives all the necessary information
• Factors that influence refractive status

  • Length of the eyeball
  • Power of the cornea
  • Power of the lens
  • Depth of anterior chamber
  • Radius of curvature
• Emmetropia


  Posterior principal point is focused on the retina with accommodation relaxed
• Ametropia


  Variation from emmetropia (error of refraction), posterior principal point is focused in front or behind the retina with accommodation relaxed
• Classification of refractive status

  • Emmetropia
  • Myopia
  • Hyperopia
  • Astigmatism
• Myopia


  Refractive condition in which with accommodation relaxed parallel rays of light converge to focus in front of the retina
• Mentioned the existence of nearsightedness

  Aristotle
• Actual definition of myopia

  Johannes Kepler (1611)
• Described and classified myopia

  Donders (1866)
• Causes of myopia


  • Long axial length
  • Too strong refractive system for its axial length
  • High refractive power
  • Short/steep corneal curvature
  • Index of refraction too high in aqueous, cornea, lens nucleus/core
  • Index of refraction too low in lens cortex, vitreous
  • Increased depth of anterior chamber
  • Cataract formation
  • Diabetes mellitus
  • Hereditary
  • Prolonged near activities = enforced accommodation
• Classification of myopia by amount

  • Low (0.25-3.00 D)
  • Medium (3.00-6.00 D)
  • High (6.00 and above)
• Classification of myopia by origin

  • Correlative/simple (simple, benign, stationary; mildly progressive)
  • Component/degenerative (pathological, progressive, malignant, degenerative)
• Classification of myopia by onset and course

  • Stationary (reaches a stage with no change)
  • Temporarily progressive (temporary progress but also stop)
  • Permanently progressive (associated with 6.00 D and above)
• Classification of myopia by age-related prevalence and age of onset

  • Congenital (error present at birth)
  • Youth-onset (before age 20)
  • Early adult-onset (20-40 years old)
  • Late adult-onset (40 years old and above)
• Signs and symptoms of myopia

  • Symptoms: Blurring of vision at far, asthenopia

  Signs: Dilated pupil, squinting, starring expression, exophthalmos (high amount of myopia), myopic crescent
• Management of myopia


  • Minus/concave lenses: spectacle correction, contact lenses, orthokeratology

  Visual training

  Surgical approach - LASIK
• Management approach for myopia by age

  • Under 6 months - no correction

  Under 3 years - give correction if error is 3.00 D or more

  1. 5 years - give correction if error is 1.50 D or more
  2. 10 years - correction based on visual demand at school

  Over 10 years - correction based on improvement of visual acuity

  Change in prescription: -0.50 D
• Management approach for myopia by muscular anomaly

  • Exophoria - full correction

  Esophoria - partial correction that won't severely affect visual acuity
• Pseudomyopia


  Tonic spasm of accommodation which frequently makes an emmetrope or hyperope appear to be myopic
• Other names for pseudomyopia

  • School myopia
  • College myopia
  • False myopia
  • Refractive myopia
  • Functional myopia
• Night myopia/nocturnal myopia


  The amount of myopia that usually appears in dim illumination, uncorrected myopia is less noticeable during the day as ambient luminance reduces the size of the eye's pupil
• Causes of night myopia

  • Spherical aberration

  Chromatic aberration
• Keratoconus


  Where the corneal curvature is becoming irregular or increasing, resulting in an increase in the error of refraction and myopia
• Hyperopia


  Refractive condition of the eye in which with accommodation relaxed, parallel rays of light converge to focus behind the retina
• First identified and described the condition hyperopia


  Kastner (1855)
• Suggested the term hypermetropia


  Donders (1858)
• Used the word hyperopia


  Helmholtz (1859)
• Causes of hyperopia


  • Simple causes: short axial length, too weak refractive system for its axial length, low refractive power, long/flat corneal curvature, index of refraction too high in lens cortex and vitreous, too low in aqueous, cornea and lens nucleus/core, shallow/decreased depth of anterior chamber, old age

  Pathological causes: deformational (microphthalmos), optical edemas/tumors/trauma, curvature (cornea plana, ulcers/injuries), absence of an element (aphakia, lens displacement), index of refraction changes from metabolic changes

  Functional causes: paralysis of accommodation, spasm of accommodation
• Classification of hyperopia by degree/amount

  • Low (0.25-3.00 D)

  Medium (3.00-5.00 D)

  High (5.00 D and above)
• Classification of hyperopia by origin

  • Correlative/simple (0.25-6.00 D)

  Component/degenerative (above 6.00 D)
• Classification of hyperopia by action of accommodation

  • Total hyperopia (sum of manifest and latent)

  Manifest hyperopia (can be revealed by ordinary routine examination)

  Facultative hyperopia (amount that can be overcome by accommodation, VA is 20/20 and can be corrected by patient's own accommodation)

  Absolute hyperopia (amount that cannot be overcome by accommodation)

  Latent hyperopia (hidden amount, requires cycloplegic refraction, revealed during presbyopic age)

  Tonic latent hyperopia (relatively fixed/permanent state of spasm)

  Clonic latent hyperopia (temporary state of spasm)
• Signs and symptoms of hyperopia

  • Symptoms: Blurring of vision at near, frontal and temporal headaches, asthenopia

  Signs: Constricted pupil, convergent strabismus, vertical brow/wrinkles, endophthalmic eyes
• Management of hyperopia


  • Plus/convex lenses: spectacle prescription, contact lenses

  Visual training

  Surgical approach - more of the same procedure performed in cataract surgery
• Management approach for hyperopia by age

  • Up to age 6 - only give prescription if visual acuity is subnormal or there is asthenopia

  6 years old to end of adolescence - give correction even for small errors if there is asthenopia

  End of adolescence to presbyopia - full error is revealed and correction is given
• Management approach for hyperopia by muscular anomaly

  • Esophoria - maximum plus/full correction that won't severely affect visual acuity

  Exophoria - partial correction, full correction accompanied by base-in prism if needed
• Management approach for hyperopia by habits and vocation

  • Those who require the use of eyes for fine work - full correction
• Clonic latent hyperopia


  Temporary state of spasm