Refractive Error

Aka: Refractive Error, Refraction, Emmetropia, Hyperopia, Farsighted, Astigmatism

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II. Definitions

  1. Refraction
    1. Measured in Diopters
    2. Bending of light rays
      1. Junction of two transparent media
      2. Media must have different densities to bend light
      3. Convex lens (e.g. human eye) converges light rays
        1. Concave lens moves focal point closer to lens
        2. Distant objects have a closer focal point than near objects
      4. Concave lens (e.g. glasses correction for Myopia) diverges light
        1. Concave lens moves focal point further from lens
    3. Human eye refracts light at two locations
      1. Cornea (66% of eye's focusing power)
        1. Fixed focusing power
      2. Crystalline lens (33% of eye's focusing power)
        1. Accommodation changes lens shape to focus objects
    4. Refractive power of lens
      1. Reciprocal of focal length measured in meters
      2. Examples
        1. One diopter lens has focal point of 1 meter
        2. Two diopter lens has focal point of 0.5 meters
  2. Emmetropia (normal Vision)
    1. Eye focusing power perfectly matched to globe length
    2. Image focused precisely on Retina
    3. Normal Vision confers focal length of infinity
  3. Myopia (Nearsightedness)
    1. See Myopia
    2. Near objects are seen best
      1. Light is focused in front of the Retina
  4. Hyperopia (Farsightedness)
    1. Far objects are seen best
      1. Light is focused behind the Retina
    2. Normal in infants (+0.50 to +2.50 Diopters)
      1. Vision normalizes by age 5 to 8 years old
    3. Light rays focus behind Cornea
      1. Cornea too flat or lens too weak for globe
      2. Near objects not seen clearly
    4. Correction: Convex lenses (convergent, plus power)
    5. Causes
      1. May be congenital with early onset
      2. Presbyopia occurs with normal aging (age >45 years)
  5. Astigmatism
    1. Non-spherical Corneal surface
      1. Represents a cylindrical Refractive Error
      2. Contrast with Myopia and Hyperopia which are spherical Refractive Errors
    2. Parts of surface (Meridians) are steeper than others
      1. Objects appear blurry at any distance
    3. Corrected with cylindrical lens oriented to appropriate axis
      1. Typically used in combination with spherical lens to correct Myopia or Hyperopia

III. Assessment

  1. See Visual Acuity

IV. Management: Refractive Error Correction

  1. Corrective lens prescriptions
    1. Example
      1. OD: -1.5 + 0.25 x180
      2. OS: -2.0 + 0.50 x180
    2. Interpretation
      1. Side (OD, OS)
      2. Spherical Lens
        1. Minus (convex) or Plus (concave)
        2. Diopter
      3. Cylindrical Lens correction
        1. Diopter
        2. Axis in Degrees
      4. Additional bifocal prescription
        1. Denoted with, for example, "Add +1.25 OU"
  2. Non-Surgical Options
    1. Eye Glasses
    2. Contact Lenses
  3. Refractive Surgery
    1. Laser In-Situ Keratomileusis (LASIK)
    2. Intrastromal corneal ring (ICR or Intacs)
    3. Phakic Intraocular Lenses

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Related Studies

Ontology: Astigmatism (C0004106)

Definition (MSHCZE) Refrakční vada oka, při níž vlivem nestejného zakřivení lomivých struktur oka (obv. rohovky, méně často čočky) dochází k poruše vidění. Světelné paprsky nedopadají na sítnici rovnoměrně, a proto nejsou pozorované předměty vnímány stejně ostře. Při zobrazení bodu ležícího mimo osu prochází úzký svazek paprsků čočkou šikmo, vlnoplocha za čočkou není kulová (má různé poloměry křivosti), vznikají dva ostré obrazy bodu ve tvaru dvou navzájem kolmých úseček, v jiných rovinách je obrazem bodu neostrá ploška. Vadu je možné upravit brýlemi s cylindrickými čočkami. (cit. Velký lékařský slovník online, 2013 http://lekarske.slovniky.cz/ )
Definition (MSH) Unequal curvature of the refractive surfaces of the eye. Thus a point source of light cannot be brought to a point focus on the retina but is spread over a more or less diffuse area. This results from the radius of curvature in one plane being longer or shorter than the radius at right angles to it. (Dorland, 27th ed)
Definition (CSP) optical defect in which refractive power is not uniform in all directions (meridians); light rays entering the eye are bent unequally by different meridians, which prevents formation of a sharp image focus on the retina.
Concepts Disease or Syndrome (T047)
MSH D001251
ICD9 367.20, 367.2
ICD10 H52.2 , H52.20
SnomedCT 193627002, 193626006, 155134009, 82649003
English Astigmatism, Astigmatism, unspecified, ASTIGMATISM, astigmatism, astigmatism (diagnosis), Astigmatism NOS, Unspecified astigmatism, Astigmatism [Disease/Finding], Astigmatism NOS (disorder), Unspecified astigmatism (disorder), Astigmatism (disorder), Astigmatism, NOS
Dutch astigmatisme, niet-gespecificeerd, astigmatisme, Astigmatisme
French Astigmatisme, non précisé, Astigmatisme
German Astigmatismus, unspezifisch, Astigmatismus, Stabsichtigkeit, Brennpunktlosigkeit
Italian Astigmatismo, non specificato, Astigmatismo
Portuguese Astigmatismo NE, Astigmatismo
Spanish Astigmatismo no especificado, astigmatismo, SAI, astigmatismo, SAI (trastorno), astigmatismo no especificado (trastorno), astigmatismo no especificado, astigmatismo (trastorno), astigmatismo, Astigmatismo
Japanese 乱視、詳細不明, 乱視, ﾗﾝｼ, ﾗﾝｼｼｮｳｻｲﾌﾒｲ
Swedish Astigmatism
Czech astigmatismus, Astigmatismus, Astigmatismus, blíže neurčený
Finnish Hajataittoisuus
Russian ASTIGMATIZM, АСТИГМАТИЗМ
Korean 난시
Croatian ASTIGMATIZAM
Polish Astygmatyzm, Niezborność
Hungarian Astigmatismus, Astigmatismus, nem meghatározott
Norwegian Skjeve hornhinner, Astigmatisme
Derived from the NIH UMLS (Unified Medical Language System)

Ontology: Hyperopia (C0020490)

Definition (MSHCZE) Dalekozrakost, porucha vidění blízkých předmětů. Typ refrakční vady oka, kdy se světelné paprsky lámou do oblasti za sítnicí (resp. kdy by ostrý obraz vznikal až za sítnicí). Příčinou je nedostatečná síla lomivého aparátu oka nebo je příliš krátká oční předozadní osa. Postižený musí nahrazovat lomivou sílu čočky značnou akomodací, pomocí níž umísťuje paprsky (resp. ostrý obraz) na sítnici. Později již ani akomodace nestačí, a tak se vidění blízkých předmětů zhoršuje. Dalekozrakost se upravuje brýlemi se spojkami (konvexní čočky – označují se znaménkem plus). (cit. Velký lékařský slovník online, 2013 http://lekarske.slovniky.cz/ )
Definition (MSH) A refractive error in which rays of light entering the eye parallel to the optic axis are brought to a focus behind the retina, as a result of the eyeball being too short from front to back. It is also called farsightedness because the near point is more distant than it is in emmetropia with an equal amplitude of accommodation. (Dorland, 27th ed)
Concepts Disease or Syndrome (T047)
MSH D006956
ICD9 367.0
ICD10 H52.0
SnomedCT 38101003, 155132008
English Farsightedness, Hypermetropia, Hyperopia, hypermetropia, hypermetropia (diagnosis), Long-sighted, Hyperopia [Disease/Finding], far-sightedness, farsighted, far sightedness, hyperopia, Long;sight, long sighted, Longsightedness, Longsighted, Farsighted, Hypermetropia (disorder), farsightedness, Far-sightedness, long sight
Dutch verziend, hyperopie, hypermetropie, Hypermetropie, Verziendheid
French Hyperopie, Hypermétrope, Hypermétropie
German weitsichtig, Hypermetropie, Hyperopie, Weitsichtigkeit
Italian Presbite, Ipermetrope, Ipermetropia, Iperopia
Portuguese Presbita, Hipermétrope, Hipermetropia, Hiperopia
Spanish Hipermétrope, Vista larga, hipermetropía (trastorno), hipermetropía, hiperopía, vista lejana, presbicia, vista larga, Hipermetropía, Hiperopía
Swedish Översynthet
Japanese ｴﾝｼ, 遠視
Czech dalekozrakost, Hypermetropie, Dalekozraký, Dalekozrakost, Hypermetrop, hyperopie, hypermetropie
Finnish Kaukotaittoisuus
Russian GIPEROPIIA, GIPERMETROPIIA, DAL'NOZORKOST', ГИПЕРМЕТРОПИЯ, ГИПЕРОПИЯ, ДАЛЬНОЗОРКОСТЬ
Korean 원시
Croatian HIPEROPIJA
Polish Nadwzroczność
Hungarian Hyperopia, Hypermetropia, Távollátó
Norwegian Langsynthet, Overlangsynthet, Hypermetropi
Derived from the NIH UMLS (Unified Medical Language System)

Ontology: Emmetropia (C0234622)

Definition (MSH) The condition of where images are correctly brought to a focus on the retina.
Concepts Finding (T033)
MSH D058453
SnomedCT 147959009, 45089002
English Emmetropias, Emmetropia, normal vision, emmetropia, emmetropias, Normal vision, Normal vision (finding)
French Emmétropie
German Emmetropie
Czech emetropie
Italian Emmetropia
Spanish Emetropía, emetropía, visión normal (hallazgo), visión normal
Russian EMMETROPIIA, ЭММЕТРОПИЯ
Portuguese Emetropia
Polish Oko miarowe, Emmetropia, Miarowość oka, Miarowość oczu
Norwegian Emmetropi
Derived from the NIH UMLS (Unified Medical Language System)

Ontology: Refraction assessment (C0430943)

Concepts Diagnostic Procedure (T060)
SnomedCT 82555003, 252886007
English Ocular refraction procedure (procedure), Ocular refraction procedure, Refraction assessment (procedure), Ocular refraction procedure, NOS, Refraction, Refraction assessment
Spanish procedimiento de refracción ocular (procedimiento), procedimiento de refracción ocular, evaluación de la refracción (procedimiento), evaluación de la refracción
Derived from the NIH UMLS (Unified Medical Language System)

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