Refractive Status

• 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
• 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

  1. 5 years: give correction if error is >=1.50 D
  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)

  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 correction 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, 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 is also based on habits and vocation, those who require extensive use of eyes for fine work will be given more plus correction
• Clonic latent hyperopia


  Temporary state of spasm