Ophthalmology Book

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Refractive Error

Aka: Refractive Error, Refraction, Emmetropia, Hyperopia, Farsighted, Astigmatism
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  1. 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. 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
    4. Hyperopia (Farsightedness)
      1. Normal in infants (+0.50 to +2.50 Diopters)
        1. Vision normalizes by age 5 to 8 years old
      2. Light rays focus behind Cornea
        1. Cornea too flat or lens too weak for globe
        2. Near objects not seen clearly
      3. Correction: Convex lenses (convergent, plus power)
    5. Astigmatism
      1. Non-spherical Corneal surface
      2. Parts of surface (Meridians) are steeper than others
      3. Objects blurry at any distance
  2. Assessment
    1. See Visual Acuity
  3. Management: Refractive Error Correction
    1. Non-Surgical Options
      1. Eye Glasses
      2. Contact Lenses
    2. Refractive Surgery
      1. Laser In-Situ Keratomileusis (LASIK)
      2. Intrastromal corneal ring (ICR or Intacs)
      3. Phakic Intraocular Lenses

Refraction assessment (C0430943)

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


Astigmatism (C0004106)

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 155134009, 193626006, 193627002, 82649003
English Astigmatism, Astigmatism, NOS, Astigmatism NOS, Astigmatism, unspecified, Unspecified astigmatism, ASTIGMATISM, astigmatism, astigmatism (diagnosis), Unspecified astigmatism (disorder), Astigmatism NOS (disorder), Astigmatism [Disease/Finding], Astigmatism (disorder)
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, Astigmatism, astigmatismo (trastorno), astigmatismo no especificado (trastorno), astigmatismo no especificado, astigmatismo, SAI (trastorno), astigmatismo, SAI, 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
Sources
Derived from the NIH UMLS (Unified Medical Language System)


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 Vision, normal, Emmetropias, Emmetropia, normal vision, emmetropia, emmetropias, Normal vision, Normal vision (finding)
Spanish Normal vision, Emetropía, Emetropia, emetropía, visión normal (hallazgo), visión normal
French Emmétropie
German Emmetropie
Czech emetropie
Italian Emmetropia
Russian EMMETROPIIA, ЭММЕТРОПИЯ
Portuguese Emetropia
Sources
Derived from the NIH UMLS (Unified Medical Language System)


Hyperopia (C0020490)

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 155132008, 38101003
English Farsightedness, Hypermetropia, Hyperopia, HYPEROPIA, hypermetropia, far-sightedness, hypermetropia (diagnosis), Long-sighted, Hyperopia [Disease/Finding], farsighted, far sightedness, farsight, Long;sight, long sighted, Hypermetropia (farsightedness), Farsighted, Hypermetropia (disorder), hyperopia, 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, Hypermetropia, hipermetropía (trastorno), hipermetropía, hiperopía, vista lejana, presbicia, vista larga, Hipermetropia, Hiperopia, Hipermetropía, Hiperopía
Swedish Översynthet
Japanese ｴﾝｼ, 遠視
Czech hyperopie, dalekozrakost, Hypermetropie, Dalekozraký, Dalekozrakost, Hypermetrop
Finnish Kaukotaittoisuus
Russian GIPEROPIIA, GIPERMETROPIIA, DAL'NOZORKOST', ГИПЕРМЕТРОПИЯ, ГИПЕРОПИЯ, ДАЛЬНОЗОРКОСТЬ
Korean 원시
Croatian HIPEROPIJA
Polish Nadwzroczność
Hungarian Hyperopia, Hypermetropia, Távollátó
Sources
Derived from the NIH UMLS (Unified Medical Language System)


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