Ophthalmology Book

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Refractive ErrorAka: 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

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.
ConceptsDisease or Syndrome (T047)
ICD9367.2, 367.20
MSHD001251
EnglishAstigmatism, Unspecified astigmatism
Spanishastigmatismo, astigmatismo no especificado
Parent ConceptsRefractive Errors (C0034951), Astigmatism (C0004106), Disorder of refraction AND/OR accommodation (C0339670), Duplicate concept (C1274013)
SourcesAOD, COSTAR, CSP, CST, DXP, ICD9CM, LCH, MEDLINEPLUS, MSH, NDFRT, OMIM, SCTSPA, SNOMEDCT
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)
ConceptsDisease or Syndrome (T047)
ICD9367.0, 367.0
MSHD006956
Englishfar-sightedness, Farsightedness, Hypermetropia, Hyperopia
Spanishhipermetropia, hiperopia, presbicia, vista larga, vista lejana
Parent ConceptsRefractive Errors (C0034951), Disorder of refraction AND/OR accommodation (C0339670), Duplicate concept (C1274013)
SourcesAOD, COSTAR, CSP, CST, DXP, ICD9CM, LCH, MEDLINEPLUS, MSH, MTHICD9, NDFRT, OMIM, SCTSPA, SNOMEDCT
Derived from the NIH UMLS (Unified Medical Language System)


Normal vision (C0234622)

ConceptsFinding (T033)
EnglishEmmetropia, Normal vision
Spanishemetropia, vision normal
Parent ConceptsGeneral visual observation (C0578652), Duplicate concept (C1274013)
SourcesOMIM, SCTSPA, SNOMEDCT
Derived from the NIH UMLS (Unified Medical Language System)


Refraction assessment (C0430943)

ConceptsDiagnostic Procedure (T060)
EnglishOcular refraction procedure, Refraction, Refraction assessment
Spanishevaluacion de la refraccion, procedimiento de refraccion ocular
Parent ConceptsVision Tests (C0042793), Procedure on eye (C0196950), Ophthalmological and optical investigations (C0455798), Duplicate concept (C1274013)
SourcesMTH, SCTSPA, SNOMEDCT
Derived from the NIH UMLS (Unified Medical Language System)



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