L3 - 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
  • 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

  • Blurring of vision at far
  • Asthenopia
  • 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 old - give correction if error is 3.00 D or more
  • 3-5 years old - give correction if error is 1.50 D or more
  • 5-10 years old - correction based on visual demand at school
  • Over 10 years old - 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
• Symptoms of night myopia


  • Blur vision only in low luminance
  • Feeling of discomfort while maintaining fixation in low illumination level
  • Difficulty in night driving and halos around light
• 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


  • 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, vitreous
  • Index of refraction too low in aqueous, cornea, lens nucleus/core
  • Shallow/decreased depth of anterior chamber
  • Old age
  • Deformational: pathologically shorter axial length
  • Microphthalmos
  • Optical edemas, tumors, trauma
  • Curvature: shallowness of corneal curvature
  • Cornea plana
  • Ulcers, injuries of cornea
  • Absence of an element (aphakia)
  • Lens displacement
  • Metabolic changes causing alteration in index of refraction
  • 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 (error from 0.25-6.00 D)
  • Component/degenerative (errors 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

  • Blurring of vision at near
  • Frontal and temporal headaches
  • Asthenopia
  • Constricted pupil
  • Convergent strabismus
  • Vertical brow/wrinkles
  • Endophthalmic eyes
• Management of hyperopia


  • Plus/convex lenses (spectacle prescription, contact lenses)
  • Visual training
  • Surgical approach (similar to 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 extensive use of eyes for fine work - full correction