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ASTIGMATISM. ASTIGMATISM: PROGRAM. Astigmatism: program. Definition Epidemiology Classification Symptoms and signs Methods of measurement Prescription criteria Resolution of clinical cases. ASTIGMATISM: DEFINITION. Astigmatism: definition .

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astigmatism program3
Astigmatism: program
  • Definition
  • Epidemiology
  • Classification
  • Symptoms and signs
  • Methods of measurement
  • Prescription criteria
  • Resolution of clinical cases
astigmatism definition5
Astigmatism: definition
  • Refractive condition in which the image of an object is not formed on a solo plane, since the different ocular meridians are of distinct potency (distinct focal distances).
  • Habitually, there are 2 main meridians, of maximum and minimum potency, and perpindicular to one another.
astigmatism epidemiology i
Astigmatism: epidemiology I
  • The majority of eyes show weak astigmatism.
  • Astigmatism can present itself in an isolated form or, with greater frequency, associated with myopia or hypermetropia.
  • Between 2-6% of the population has an astigmatism > 2,00 dioptre
astigmatism epidemiology ii
Astigmatism: epidemiology II
  • Changes with age
    • An significant percentage of newborns show inverse astigmatism.
    • During the first few months of life the astigmatism dimishishes gradually.
    • At school age, direct astigmatism of low magnitude tends to exist.
    • Throughout youth and adulthood, astigmatisms do not tend to pass through any important changes.
    • From the 50-60 and on, increases in inverse astigmatism or decreases in direct astigmatism exist.
astigmatism epidemiology iii
Astigmatism: epidemiology III
  • Genetics
    • In corneal astigmatisms >1,50/2,00D there is a strong genetic component
  • Environmental factores
    • The use of rigid contact lenses can induce variations in the corneal astigmatism of 2 or more dioptres.
  • Various authors suggest that astigmatism and its variations are the consequence of the relationship between the palpebral tarsus and the cornea.
astigmatism c lassification i
Astigmatism: classification I
  • According to the regularity of the corneal surface
  • According to the direction of the main meridians
  • According to the refraction of the eye
astigmatism c lassification ii
Astigmatism: classification II
  • According to regularity of the corneal surface
    • Regular (habitual):
      • Main meridians are perpindicular to one another
    • Irregular (infrequent):
      • Main meridians are not perpindicular
      • Curvature of one of the meridians is not constant

Irregular corneal astigmatism

Regular corneal astigmatism

Spherical cornea

astigmatism classification iii

90°

70°

110°

135°

45°

160°

20°

180°

Astigmatism: classification III
  • According to the direction of the main medians of the astigmatism of the eye
    • Direct astigmastism or “in favor of the rule”
      • The horizontal meridian is the flattest
      • The horizontal meridian is less powerful
      • The axis of the refractive astigmatism, expressed in negative potency, is around 0º-180º (±20º)
      • It is the most frequent
astigmatism classification iv

90°

70°

110°

135°

45°

160°

20°

180°

Astigmatism: classification IV
  • According to the direction of the main meridians of the astigmatism of the eye
    • Inverse astigmatism or “against the rule”
      • The vertical meridian is the flattest
      • The vertical meridian is less powerful
      • The axis of the refractive astigmatism, expresed in negative potency, is around 90º (±20º)
astigmatism classification v

90°

70°

110°

135°

45°

160°

20°

180°

Astigmatism: classification V
  • According to the direction of the main meridians of the astigmatism of the eye
    • Oblique astigmatism
      • The main meridians are between 20° and 70° and between 110° and 160°
astigmatism classification vi
Astigmatism: classification VI
  • According to the refraction of the eye:
    • Simple: only one meridian is ametrope (only astigmatism exists).
      • Example 1: -0,50x90º (simple myopic astigmatism)
      • Example 2: +1,25x5º (simple hypermetropic astigmatism)
    • Compound: the two meridians show the same type of ametropia.
      • Example 1: +2,50+1,75x15º (Compound hypermetropic astigmatism)
      • Example 2: -1,00-0,75x30º (Compound myopic astigmatism)
    • Mixed: the two meridians are ametropic and of a different type.
      • Example 1: +0,50-1,50x10º (the potency of one meridian is +0,50 and the other -1,00)
astigmatism classificaction vii

Simple H. Astig.

Compound H. Astig.

Simple M. Astig.

Compund M. Astig.

Mixed Isodioptric Astig.

Mixed Isodioptric Astig.

Astigmatism: classificaction VII
  • In the following schemes the formation of images in the retina according to the eye’s refraction are shown:
astigmatism classification viii
Optical cross:

The weaker meridian (flattest) is the one at 180º

Transposition formula:

+1,50+2,00x90º

Classification according to main meridians:

Direct astigmatism

Classification according to refraction:

Compound hypermetropic astigmatism

+3,50-2,00=+1,50

+3,50

Astigmatism: classification VIII

Example 1: +3,50-2,00x180º

astigmatisms symptoms and signs i
Astigmatisms: symptoms and signs I
  • The symptoms tend to depend on the magnitude of the astigmatism.
    • Moderate and evelated astigmatism
      • Blury vision in DV and NV
      • Symptoms of visual fatigue, headache, ocular irritation, etc.
      • Symptoms of image distortion and absence of comfort upon initial use of lenses that compensate for astigmatism
astigmatisms symptoms and signs
Astigmatisms: symptoms and signs
  • Low astigmatism (<1,50D)
    • The VA does not tend to be very affected, but it is difficult to determine it precisely
    • Visual fatigue associated with prolonged use of vision
    • Inverse astigmatisms tend to produce greater symptomology than direct ones
    • Significant difficulties to adapt to the new prescription do not tend to appear
astigmatisms symptoms and signs iii
Astigmatisms: symptoms and signs III
  • Imprecision in the determination of VA
    • Low astigmatisms < 1.50 D
      • If it is hypermetropic the VA can easily reach 20/25 or even 20/20
      • If it is myopic the VA is affected more and is near 20/30
    • Moderate to high astigmatisms (≥1,50-2,00 D)
      • If it is hypermetropic the VA is diminished, but not as much as it would be if it were myopic
      • If it is hypermetropic the diminishment of the VA will be ≈ in DV and in NV
      • If it is myopic the diminishment of the VA will be greater in DV than in NV
    • Oblique astigmatisms demonstrate the worst VA
      • Comparing the same level, the VA in the oblique astigmatism < VA in inverse astigmatism < VA in direct astigmatism
astigmatism methods of measurement i
Astigmatism: methods of measurement I
  • Keratometry: determination of the power of the main meridians of the cornea
    • Hemholtz
    • Javal
    • Automatics
  • Corneal topography: determination of the morphology of the anterior corneal surface
astigmatism methods of measurement ii
Astigmatism: methods of measurement II
  • Keratometry:
    • Clinical technique to measure the radius of the curvature of the anterior face of the cornea.
    • Based on the reflection of light in the cornea (convex mirror). It gives a small image, straight and virtual, of the object (“look”) which is of a known size
    • The measurement is done in a diameter of 3 mm around the visual axis
astigmatism methods of measurement iii
Astigmatism:methods of measurement III
  • Hemholtz’s keratometer
  • Javal’s keratometer
  • Automatic keratometers
astigmatism methods of measurement iv
Astigmatism: methods of measurement IV
  • Corneal topography:
    • Can measure large areas
    • Is a quantitative evaluation
    • High resolution (approx. 5000 puntos)
    • Lots of presentation options
astigmatism methods of measurement v
Astigmatism: methods of measurement V
  • Clinical use
    • Informs on the quality/integrity of the corneal surface
      • regular : clear and regular vision and the main meridians are perpindicular
      • Irregular: irregular or distorted vision. The precise determination of the main meridians is difficult
    • Help in the determination of approximante astigmatic refraction
      • In cases of minimal collaboration
      • When ocular means are unclear
    • Essential help in the selection of parameters for contact lenses
astigmatism methods of measurement vi
Astigmatism: methods of measurement VI
  • Limitations of keratometry:
    • An astigmatism determined through keratometry corresponds to the anterior face of the cornea.
      • Astigmatism also exists in the posterior face of the cornea, being crystalline and even retinal.
    • The design of the keratometer is based on spherical surfaces and this leads to errors in the measurement
    • The visual axis frequently remains displaced from the geometric center of the cornea
    • The measurement is done is a 3 mm diameter around the visual axis
astigmatism methods of measurement vii
Astigmatism: methods of measurement VII
  • The total astigmatism (TA) is the sum of:
    • Astigmatism of the anterior face of the cornea (FHC)
    • Internal physiological astigmatism (IPA)
  • Javal’s rule:
    • In general, the IPA has an approximate value of

-0,50x90º

  • Example 1:
    • FHC = -1,75x180º
    • Which TA is expected, if we follow Javal’s rule?
astigmatism prescription criteria i
Astigmatism: prescription criteria I
  • Age of the patient:
    • Small children (from 2 to 6): total compensation if the VA is believed to be compromised. There tends to be good tolerance.
    • Children (from 6 to 12): total compensation continues being recommended, but the tolerance tends to lessen.
    • Adults: Variable tolerance to the changes:
      • If there are great improvements of the VA: prescribe for the astigmatism
      • Oblique axes: partial compensation of the astigmatism
astigmatism prescription criteria ii
Astigmatism: prescription criteria II
  • Magnitude of the astigmatism:
    • The greater the astigmatism, the lesser the tolerance to the total prescription
    • Elevated astigmatisms tend to be congenital or of early appearance. If no prescription is made, they can provoke ambyopia.
    • In cases of irregular elevated astigmatisms the best VA is obtained through the use of rigid contact lenses.
    • Small astigmatisms (<1,00D) do not tend to require serious consideration.
astigmatism prescription criteria iii
Astigmatism: prescription criteria III
  • Habitual astigmatic prescription:
    • When an adult patient does not show symptoms with his/her habitual compensation, it seems wise not to realize important changes.
    • Consider changes when symptoms, marked reduction of the VA or reduction of stereopsis exists.
    • For adults that have never had astigmatism:
      • Reduce the cylindrical power, maintaining the spherical equivalent.
      • With the passage of time try to align the level of prescription to the refraction of the person.
astigmatism prescription criteria iv
Astigmatism: prescription criteria IV
  • Method of the spherical equivalent (SE)
    • Method to reduce the power of the cylinder but allowing that, without additional accomadative force, the circle of least confusion is situated over the retina.
    • Half of the magnitude of the unprescribed cylinder (SE) sums up algebraically to the value of the sphere
    • Example 1: +2,50-3,50x85º
      • 2,00 dioptres are prescribed
      • SE of the unprescribed astigmatism = -1,50/2 = -0,75
      • The SE adds up to the value of the sphere: +2,50 +(-0,75) = +1,75
      • Final prescription: +1,75-2,00x85º
astigmatism case 1 i
Astigmatism: case 1-I
  • MJH, 12-year-old child. Student.
  • MC: Occasionally shows that he does not see well in NV. Visual tiredness when studying. Occasional ocular hyperaemia.
  • PH: Has never worn glasses. Previous pediatric check-ups. No illnesses or ingestion of medication.
  • FH: Unimportant.
astigmatism case 1 ii
Astigmatism: case 1-II
  • Habitual VA in DV and NV:
    • RE: 20/20-2; NV: 20/25
    • LE: 20/25; NV: 20/25
  • Binocularity in habitual conditions:
    • Cover test:
      • DV: ortho
      • NV: ortho
    • Proximal convergence: 5/8cm
astigmatism case 1 iii
Astigmatism: case 1-III
  • Retinoscopy:
    • RE: +1,00-1,50x180º
    • LE: +0,50-1,50x5º
  • Subjective DV and VA:
    • RE: +0,50-1,25x175º; VA: 20/20
    • LE: +0,25-1,25x5º; VA: 20/20
    • NV with the subjective: VA 20/20 in both eyes. Good comfort
  • Amplitude of accomodation with the subjective:
    • RE: 8cm≈12,5D
    • LE: 8cm≈12,5D
  • Ocular health exams: within normal limits
  • Color vision: normal
astigmatism case 1 iv
Astigmatism: case 1-IV
  • Complete diagnostic of the case
  • Proposed treatment and plan of check-ups
  • Possible evolution of the condition
astigmatism case 1 v
Astigmatism: case 1-V
  • Complete diagnostic of the case
    • Low hypermetropia present in both eyes
    • Direct astigmatism in both eyes:
      • According to the conoid: mixed in both eyes
    • Binocularity and accomodation: within the normal limits
    • Other tests within normal limits
astigmatism case 1 vi
Astigmatism: case 1-VI
  • Proposed treatment:
    • Glasses with the value of the subjective:
      • RE: +0,50-1,25x175º
      • LE: +0,25-1,25x5º
    • Use mainly for school and work in NV.
    • They can be worn for all uses.
    • Revision in one year or before if new symptomology appears.
    • Explain the condition to the patient and his/her parents.
astigmatism case 1 viii
Astigmatism: case 1-VIII
  • Possible evolution of the condition:
    • Stability of the stigmatism
    • Slight diminishment (or stability) of the hypermetropia
astigmatism case 2 i
Astigmatism: case 2-I
  • JJB, 25-years-old. Waiter.
  • MC: Notices sporadic diminishment of vision, as much in DV as in NV. Greater difficulty at the end of the day.
  • PH: 15 years ago he was prescribed glasses but they were very uncomfortable and he never wore them. No illnesses or ingestion of medication.
  • FH: Irrelevant.
astigmatism case 2 ii
Astigmatism: case 2-II
  • Habitual VA in DV y NV:
    • RE: 20/40; NV: 20/40
    • LE: 20/30; NV: 20/25
  • Binocularity in habitual conditions:
    • Cover test:
      • DV: ortho
      • NV: ortho
    • Proximal convergence: as far as the nose
astigmatism case 2 iii
Astigmatism: case 2-III
  • Retinoscopy:
    • RE: +3,00-4,00x5º
    • LE: +1,50-2,50x20º
  • Subjective DV and VA:
    • RE: +2,75-3,50x5º; VA: 20/25
    • LE: +1,00-2,00x15º; VA: 20/20+
    • DV and NV with the subjective: notices better vision but is not comfortable. A reduction of the graduation is tried and tolerance is greater:
      • RE:+2,00-2,00x5º; VA: 20/25-2
      • LE: +0,75-1,50x15º; VA: 20/20
  • Amplitude of accomodation with the second refraction:
    • RE: 14cm≈7D
    • LE: 11cm≈9D
  • Exams of ocular health: within normal limits
    • Central fixation in both eyes
astigmatism case 2 iv
Astigmatism: case 2-IV
  • Are other tests necessary for a correct diagnosis and treatment?
  • Complete diagnosis of the case
  • Proposed treatment and plan of check-ups
  • Possible evolution of the condition
astigmatism case 2 v
Astigmatism: case 2-V
  • Are other tests necessary for a correct diagnosis and treatment?
    • VA with a stenopaic disc?
    • Keratometry?
astigmatism case 2 vi
Astigmatism: case 2-VI
  • Complete diagnosis of the case
    • Hypermetropic and astigmatic anisometropia
    • Hypermetropia becomes apparent in both eyes (RE>LE)
    • Direct astigmatism in both eyes (RE>LE)
      • According to the conoid: mixed astigmatism in both eyes
    • Slight amblyopia in the RE
    • The rest of the tests within normal limits
astigmatism case 2 vii
Astigmatism: case 2-VII
  • Proposed treatment:
    • Prescribe glasses with the determined equivalent:
      • RE:+2,00-2,00x5º
      • LE: +0,75-1,50x15º
    • Use as much in DV as in NV.
    • Explain the condition to the patient
    • New revision in 3-4 months
astigmatism case 2 viii
Astigmatism: case 2-VIII
  • Possible evolution of the condition:
    • Significant changes to the value of the refractive defect are not expected in the first few years
    • Periodical check-ups are necessary since we want to get the prescription as near as possible to the value of the refractive defect
    • Greater dependence on glasses with the passage of time
astigmatism bibliography
Astigmatism: bibliography
  • Amos JF. Diagnosis and management in vision care. Butterworth-Heinemann, 1987
  • Grosvenor T, Flom MC. Refractive anomalies. Research and clinical applications. Butterworth-Heinemann, 1991
  • Brookman KE. Refractive management of ametropia. Butterworth-Heinemann, 1996
  • Werner DL, Press LJ. Clinical pearls in refractive care. Butterworth-Heinemann, 2002
astigmatism bibliography49
Astigmatism: Bibliography
  • http://en.wikipedia.org/wiki/Astigmatism
  • http://www.healthatoz.com/healthatoz/Atoz/ency/astigmatism.jsp
  • http://www.eyemdlink.com/Condition.asp?ConditionID=250