1. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
ASTIGMATISM
The objective of this section is: Determine the prescription criteria in cases in which subjects have astigmatism.
This section is structured to include:
2 hours of theory
1 hour of work outside of the classroom
It does not deal with directly associated skills or methods. Simultaneously, we recommend that students continue drilling clinincal techniques of refraction.

2. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
ASTIGMATISM: PROGRAM

3. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: program
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
Definition
Epidemiology
Classification
Symptoms and signs
Methods of measurement
Prescription criteria
Resolution of clinical cases
This astigmatism theme will address, in order, the points shown in the slide above.

4. ASTIGMATISM: DEFINITION
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
ASTIGMATISM: DEFINITION
In the section dedicated to definition, the objective is to refresh the student’s previous knowledge of astigmatisms, explained in an earlier module. Therefore, this class doesn’t necessarily have to be attended in person. We can count on between 1 to 2 hours of personal work by the student in order to recuperate previous knowledge
We recommend working in groups of 3-4 students, guiding them in the following phases:
Recuperation of the information learned from other subjects/courses.
Recommend a bibliography or webpage covering the subject of astigmatism
A professor’s interview with each of the groups in which strong and weak points of the summary realized up to that point are detected. Elaboration and amplification necessary for each group.
A definitive work handed in to the professor who can decide what does and does not form a part of the system of evaluation.
A later, corrected work handed in indicating the quality of the work and assessing the capacity for synthesis.
At this point it is very important to make sure that the student:
Knows to convert the ocular refraction in its representation in a cross-cylinder and viceversa
Knows how to transpose a sphero-cylindrical formula and pass it from the negative cylinder to the positive and viceversa.
To this end we recommend a series of exercises of a type similar to:
Exercise 1: +2,00-1,00x180º
a. Mould the cross-cylinder
b. Which is the least powerful meridian?
c. Transpose the formula, passing it to the positive cylinder

5. Astigmatism: definition
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: definition
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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.
In the astigmatic eye the rays of light coming from infinity do not focus in one point, like they do in the emmetropic, myopic or hypermetropic eye, since all the ocular meridians do not possess the same potency. In regular astigmatism, the norm, the changes of refraction from one meridian to another are progressive, from which the final result is reduced to two main meridians, of greater and lesser refractive power, and perpindicular to one another.
In the images inserted into the slide we can see, in a schematic way, the depicted formation of images. It is necessary to remind the students that the zone of focalization is known as Sturn’s conoid and that it is in the intermediate zone where the image is of the highest quality and is known as the circle of least confusion.

6. Astigmatism: epidemiology I
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: epidemiology I
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
According to epidemiologists, the refractive defect with the greatest prevalence is astigmatism since the majority of people show a low level of astigmatism that doesn’t tend to exceed 0.50 diotropes. When we refer to medium or elevated astigmatisms, prevalence diminishes markedly, situating itself around 2-6%.

7. Astigmatism: epidemiology II
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: epidemiology II
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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 and on, increases in inverse astigmatism or decreases in direct astigmatism exist.
Las variaciones habituales del astigmatismo a lo largo de la vida se reflejan en la diapositiva. Destacamos que el astigmatismo varía los primeros años de vida, llegando a estabilizarse en los niveles del adulto hacia los 5-6 años de vida. El proceso es:
Durante las primeras semanas del recién nacido se ha encontrado un grado significativo de astigmatismo inverso que irá disminuyendo en los meses siguientes.
A partir de los 6 años los estudios muestran una mayor prevalencia de bajos astigmatismos directos (inferiores a 1,00 dioptría). A partir de estas edades el valor del astigmatismo suele estabilizarse, en ausencia de patología ocular.
A partir de los 60 años suele aparecer una disminución en la magnitud de los astigmatismos directos e incluso un aumento del inverso. Se piensa que el motivo de este cambio tardío es la pérdida de tonicidad del párpado superior lo que permite un mayor aplanamiento del meridiano corneal vertical.

8. Astigmatism: epidemiology III
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: epidemiology III
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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.
In the slide, the diverse results studied on certain factors that influence astigmatism are shown.

9. Astigmatism: classification I
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: classification I
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
According to the regularity of the corneal surface
According to the direction of the main meridians
According to the refraction of the eye
Next, we dedicate an important section to the diverse forms of classifying astigmatism since they permit a greater depth and understanding of the subject. Astigmatism can be classified in different ways, but we will make reference to three criteria of clinical importance:
According to the integrity and regularity of the anterior corneal surface, we must remember it is the ocular surface that tends to collaborate principally in the existence of astigmatism.
According to the direction of the main meridians of the ocular refraction, since this factor has a significant effect on the symptomology the individual shows.
According to the total refraction of the eye, an isolated astigmatism could exist or, with greater frequency, one associated to myopia or hypermetropia.

10. Astigmatism: classification II
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: classification II
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
As we commented previously, in regular astigmatism the changes of refraction from one meridian to another are progressive, which is why the final result is reduced to two main meridians of greater and lesser refractive power and perpindicular to one another. It is the most commonly found astigmatism.
Irregular astigmatism tends to be secondary to a pathological condition of the anterior segment of the eye. This pathology can be active or already overcome, but having already left scars or zones of irregularity on the corneal surface. In these cases there is no geometric pattern in the different meridians enabling, even, the existence of distinct powers in the same meridian. It is much more infrequent than regular astigmatism. Some of the causes of irregular astigmatism are:
Keratoconus: degenerative corneal alteration that provokes a thinning and deformation of the cornea
Corneal abrasions and erosions
Chalazion: palpebral alteration that through pressure upon the cornea can come to provoke an irregular astigmatism
Corneal deformation due to the use and abuse of contact lenses
Regular corneal astigmatism
Irregular corneal astigmatism
Spherical cornea

11. Astigmatism: classification III
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: classification III
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
When classifying the regular ocular astigmatism depending on the direction of the main meridians, we find the types shown in the three following slides:
Direct astigmatism: the flattest meridian, or of lesser power, shows a horizontal orientation, within the range depicted in the image .
180°
135° 0°
90°
45°
160°
110°
20°
70°

12. Astigmatism: classification IV
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: classification IV
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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)
Inverse astigmatism: the flattest meridian, or of lesser power, shows a vertical orientation, within the range depicted in the image.
180°
135° 0°
90°
45°
160°
110°
20°
70°

13. Astigmatism: classification V
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: classification V
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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°
Oblique astigmatism: the flattest meridian, or of lesser power, shows an oblique orientation within the range depicted in the image.
180°
135° 0°
90°
45°
160°
110°
20°
70°

14. Astigmatism: classification VI
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: classification VI
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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)
As commented earlier, the astigmatism can find itself isolated or, more frequently, associated with a variable magnitude of hypermetropia or myopia. Along with this factor we can find:
Simple Astigmatism: Only astigmatism exists. One meridian focuses on the retina (it is emmetrope) and the other shows hypermetropia (simple hypermetropic astigmatism) or myopia (simple myopic astigmatism. In the slide a couple of examples are shown.
Compound Astigmatism: Both main meridians show an ametropia of the same type, myopic (compound myopic astigmatism) or hypermetropic (compound hypermetropic astigmatism)
Mixed Astigmatism: Both main meridians show signs of an ametropia of distinct types, one meridian is myope and the other is hypermetrope.
The contents of this slide complement those in the following slide in which the same concepts are graphically depicted.

15. Astigmatism: classificaction VII
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: classificaction VII
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
In the following schemes the formation of images in the retina according to the eye’s refraction are shown:
Simple M. Astig.
Simple H. Astig.
Compound H. Astig.
Compund M. Astig.
Scheme of the formation of images: shows the position of Sturn’s conoid.
Mixed Isodioptric Astig.
Mixed Isodioptric Astig.

16. Astigmatism: classification VIII
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: classification VIII
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
Example 1: +3,50-2,00x180º
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
At this point we recommend assigning a series of exercises that permit the students to apply their knowledge of this section. Below we develop an example.
Let’s imagine a case in which the ocular refraction is +3,50-2,00x180º. Complete the following tasks and/or answer the questions:
Draw the corresponding optical cross
Which ocular meridian is flattest (weakest)?
Transpose the sphero-cylindrical formula
Classify the astigmatism according to the direction of the main meridians
Classify the astigmatism according to the level of refraction

17. Astigmatisms: symptoms and signs I
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatisms: symptoms and signs I
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
The symptoms of patients with astigmatism depend as much on the magnitude of the astigmatism as on the spherical ametropia that accompanies it. That is why symptoms vary in their distinct grades of severity among different individuals. Along general lines we can say that:
In cases of moderate or elevated astigmatism the VA, as much in DV as in NV, is decreased.
Patients tend to mention visual fatigue, headaches, etc., mainly when the person realizes tasks that require visual exertion. This symptomology tends to be greater when the astigmatism is accompanied by hypermetropia since an accomodative exertion is constantly made in order to situate the circle of least confusion over the retina (best image quality).
According to age in which the use of astigmatic prescription begins, symptoms of spacial distortion appear, mainly in observation of the floor, the walls, figures with straight lines, etc. It’s good to wait until an adaptation to this phenomenon occurs after a few weeks of the use of the prescribed calibration.

18. Astigmatisms: symptoms and signs
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatisms: symptoms and signs
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
In cases of astigmatism of low magnitude:
The visual acuity is not affected much. Nonetheless, the diminishment will be greater in cases in which the astigmatism is accompanied by a certain grade of myopia.
Visual fatigue, headaches, etc., mainly after realizing tasks requiring prolonged use of vision.
Adaptation to the new prescription is not as critical as it is in cases of elevated astigmatism, but it remains dependent on:
The magnitude of the astigmatism
The age of the individual
The tolerance of changes

19. Astigmatisms: symptoms and signs III
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatisms: symptoms and signs III
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Here is a small section dedicated to the characteristics of the VA in people with astigmatism, providing certain specifics depicted in the slide.

20. Astigmatism: methods of measurement I
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: methods of measurement I
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Here there is just a small description of the methods of measurement of corneal astigmatism that exist today. In the course on instrumentation, another description is made with much greater attention to detail.

21. Astigmatism: methods of measurement II
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: methods of measurement II
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Keratometry is the technique traditionally used to measure the power and radius of the main meridians of the cornea.

22. Astigmatism:methods of measurement III
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism:methods of measurement III
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
Hemholtz’s keratometer
Javal’s keratometer
Automatic keratometers
In the slide, images of commonly used keratometers are shown.

23. Astigmatism: methods of measurement IV
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: methods of measurement IV
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
Corneal topography:
Can measure large areas
Is a quantitative evaluation
High resolution (approx puntos)
Lots of presentation options
Corneal topography allows us to obtain a map of the morphology of nearly all of the anterior surface of the cornea.

24. Astigmatism: methods of measurement V
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: methods of measurement V
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Utilizing keratometry provides us with valuable information about:
The possible existence of lesions or pathologies on the anterior surface of the eye, since the vision will be distorted and it will be nearly impossible to localize the main meridians.
In some cases it can be useful in order to determine the approximate magnitude of the ocular astigmatism. Nevertheless, it is necessary to pay special attention to the fact that it is only an approximation since other ocular components exist that also contribute to the total astigmatism of the eye.
It orients us during the selection of the parameters for test contact lenses.

25. Astigmatism: methods of measurement VI
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: methods of measurement VI
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Keratometry also some limitation that we must keep in mind:
It only provides information about the astigmatism on the anterior face of the cornea. In the next slide more emphasis will be place on this concept.
Keratometers traditionally operate under the supposition that the geometry of the cornea is spherical and that the geometric center of the cornea coincides with the visual axis. These errors have been solved through the use of corneal topographies.

26. Astigmatism: methods of measurement VII
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: methods of measurement VII
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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?
As we mentioned before, the total astigmatism does not only depend on the anterior face of the cornea if not also on the astigmatism provoked on the posterior face of the cornea, the crystalline and even in the retina. The astigmatism composed of these ocular components and which is not measurable by the common clinical methods is given the name of: internal physiological astigmatism. As follows:
TA = FHC + IPA
One rule, normally accepted and contrasted in studies, was proposed by Javal and consists in supposing that the value of the IPA has an approximate value of 0,50 dioptres of inverse astigmatism. Nevertheless, it must npt be forgotten that it is an empirical rule and does not apply to all people.
It is good to provide several diverse examples for the students so that they familiarize themselves with Javal’s rule. One example is shown in the slide:
Through keratometric measurements we know that the FHC of one eye is from -1,75x180º
Javal’s rule tells us to expect an IPA of -0,50x90º (or the equivalent of +0,50x180º) that must sum up algebraically to the result of the keratometry
Consequently we expect a slightly inferior TA, in this case, than one from the anterior face of the cornea and with an approximate value of -1,25x180º

27. Astigmatism: prescription criteria I
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: prescription criteria I
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Prescription in cases of astigmatism is not simple and the following slides give a series of general guidelines regarding the diverse factors that must be considered.
Age if the patient:
In treating babies, we must be very prudent when prescribing since, as we commented in the first slides, the astigmatism can vary significantly in the first few months of life. In babies up to 2-years-old, follow-up should be accompanied by two or three check-ups before the prescription is recommended.
In small children older than 2: the prescription for the astigmatism is important in that we must always consider that it can complicate the correct visual development of the child and provoke amblyopia. We are referring to moderate or elevated astigmatism. In these cases and at these ages, a total prescription for the astigmatism is advisable since the child’s sensory plasticity is not normally accompanied by difficultites in adaption to the prescription.
A similar guideline is recommended for children between the ages of 6 and Nevertheless, in these cases there can exist greater difficulty to adapt oneself to the distortion that the compensation of elevated astigmatism provokes. It makes sense to wait for the child to adapt well after a few weeks of constant use of glasses.
In adults it is more difficult to make a decision. Along general lines:
The changes tend to more easily accepted when the come accompanied by evident improvements of the VA.
Important changes in the absence of signs or symptoms are not justifiable
Astigmatisms of oblique axes are the least tolerated because they provoke the greatest distortion of visual perception. Bias the prescription.

28. Astigmatism: prescription criteria II
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: prescription criteria II
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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.
Magnitude of the astigmatism:
It is evident to think that the greater the magnitude of the astigmatism (or of the astigmatic change detected) the greater the difficulty in tolerance of the prescription. Clinically, there are two trends in the prescription of elevated astigmatisms:
Prescribe for the totality of the astigmatism. If the patient does not adapt, after a prudent period of time, make the necesarry changes to reduce the prescription for the astigmatism.
Bias the prescriptions with astigmatisms, preventing possible complaints from the patient.
Other considerations for prescription are listed in the slide.

29. Astigmatism: prescription criteria III
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: prescription criteria III
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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.
Here we make reference to cases in which the patient already has part of his/her astigmatism compensated for with his/her glasses and questions the suitability of realizing important changes in their graduation.
When this section makes reference to the optical prescription in subjects with astigmatism the concepts of “biasing”, “reducing”, etc. the magnitude of the astigmatism in the compensation always present themselves. This means diminishing the prescription of the astigmatism is recommended, while maintaining the spherical equivalent of the graduation. This concept is important enough to merit further inspection in the next slide.

30. Astigmatism: prescription criteria IV
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: prescription criteria IV
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
In this slide the objective of and method to bias the prescriptions for astigmatism is explained.
Objective: situate, in a relaxed way and without accomadative force, the circle of least confusion over the retina.
Method: half of the unprescribed astigmatism sums up algebraically to the value of the sphere
An example is shown, but it would be advisable to realize various examples in order to familiarize the students with the method.

31. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
ASTIGMATISM: CASES
Next, two cases of hypermetropic patients are presented. The objective is to present the cases to the students and allow them 15 minutes to try and solve the questions displayed at the end. It might be more adequate to have them work in groups.

32. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 1-I
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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.
Some clarifications about the slide:
MJG are the initials of the patient’s name. The existing laws that treat the protection of personal information impede revealing any patient’s name.
MC: Principal motive of the consultation
PH: personal history
FH: family history

33. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 1-II
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Results of the first clinical exams realized. We observe:
The monocular VA is slightly dimished as much in the DV as in the NV. This data informs us of the possible existence of astigmatism. It could also be a case of elevated hypermetropia.
Normally, when the VA is not very reduced, it is normal to perform an exam that will imform us as to the efficiency of the visual system in habitual conditions. In this case the result of the cover test is found within normal limits.

34. Astigmatism: case 1-III
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 1-III
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Some comments regarding the content of the slide:
The values of the retinoscopy and the subjective are similar; in addition the VA and the visual comfort in NV is suitable for the value of the subjective.
The test of the amplitude of accomodation has also been realized. It has been realized with the value of the subjective. The value is normal for his/her age.
Given that the patient is a man and that it is the first time that he has realized a complete visual exploration, a test of his color vision has also been realized.

35. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 1-IV
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
Complete diagnostic of the case
Proposed treatment and plan of check-ups
Possible evolution of the condition
These are the issues that the students should try to resolve.

36. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 1-V
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
The diagnostic is shown on the slide. It may indicate that we have not made special mention of the anisometropia since a large difference in graduation between both eyes of 0,25D is totally irrelevant.
Emphasize that in this case we have not planned the need to reduce the magnitude of the astigmatism in the prescription by three factors:
The low magnitude of the astigmatism.
The type of astigmatism: direct in both eyes and of equal magnitude.
The patient is a child of 12 which is why we do not expect difficulty in adaptation to the prescription,
We could have realized more tests of binocularity and accomodation but the most logical is to hope for an effect of the graduation on the symptomology of the child.

37. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 1-VI
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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.
The proposed course of action is displayed in the slide. Pay special attention to the fact that the glasses are needed mainly for NV and during class. They are not necessary when playing sport or participating in other outdoor activities.
The next revision could be recommended in 6 months instead of in a year.

38. Astigmatism: case 1-VIII
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 1-VIII
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
Possible evolution of the condition:
Stability of the stigmatism
Slight diminishment (or stability) of the hypermetropia
It is hoped that the refractive defect found in DV will change little in the next few years. Perhaps there could be a slight decrease of the mypermetropia but of low magnitude.

39. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 2-I
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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.
Some clarifications regarding the slide:
JJB are the initials of the patient’s name. The existing laws that treat the protection of personal information impede revealing any patient’s name.
MC: main motive for the consultation
PH: personal history
FH: family history

40. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 2-II
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Results of the first clinical exams realized. We observe:
The monocular VA is diminished as much in DV as in NV, mainly in the RE. This data informs us of the possible existence anisometropía or an important disfunction of binocularity (possible strabismus).

41. Astigmatism: case 2-III
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 2-III
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Some comments about the content of the slide:
The values of the retinoscopy and the subjective are similar
Given that the patient does not wear glasses, a comfort test was realized with the found level of refraction and we were obligated to reduce the astigmatic prescription (suiting the sphere to the reduction realized).
Also, an examination of amplitude of accomodation was done with the more comfortable refraction. A slightly reduced value was observed in the RE; this can be due to a lack of hypermetropia in the patient’s prescription and a consequence of a certain amblyopia.
To corroborate that a small angled strabismus (a microtropia) does not exist, the fixation, which is central in both eyes, was assessed. This result allows us to determine that there is no strabismus since the result of the cover test is normal.

42. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 2-IV
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
These are the questions that the students should solve.

43. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 2-V
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
Are other tests necessary for a correct diagnosis and treatment?
VA with a stenopaic disc?
Keratometry?
In this case it seems interesting to ask this question of the students. Basically, it makes reference to two sections of the slide:
The VA with a stenopaic. This test is always essential in all cases in which the VA with the best refraction is incorrect. In this case its evaluation would have been necessary.
Having and noting down the value of the patient’s keratometry would have provided interesting data for the continuation of the case.
The need for a low refraction cycloplegia could have also been questioned. Nonetheless, with the collected data it does not seem necessary.
A new cover test could also have been realized with the value of the subjective.

44. Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 2-VI
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
The diagnostic is shown in the slide.

45. Astigmatism: case 2-VII
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 2-VII
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
Distinct professionals could propose slightly different treatments, but in all of the cases aimed at prescribing a refraction, mantaining the anisometropia provides a certain equilibrium between the best vision and the comfort. One possibility is displayed in the slide.
The use of the glasses should be constant
It is just as essential to explain the visual condition to the patient as it is to recommend a follow-up revision to reevaluate:
The symptomology
A new refractive exam: retinoscopy and subjective
Possible change of the graduation of the glasses

46. Astigmatism: case 2-VIII
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: case 2-VIII
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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
In the slide, the evolution that we can expect with the passage of time is shown.

47. ASTIGMATISM: BIBLIOGRPHHY
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
ASTIGMATISM: BIBLIOGRPHHY

48. Astigmatism: bibliography
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: bibliography
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)
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

49. Astigmatism: Bibliography
Óptico de Atención Primaria (Tahoma 10 negrita y alineado izquierda)
Astigmatism: Bibliography
Asignatura
Número y Título del tel tema (Tahoma 10 negrita y alineado derecha)