Types of Astigmatism.
Based on axis of the principal meridians
Regular astigmatism –      principal meridians are perpendicular 
With-the-rule astigmatism – the vertical       meridian is steepest (an American football lying on its side).
Against-the-rule astigmatism – the       horizontal meridian is steepest (an American football standing on its       end).
Oblique astigmatism – the steepest curve       lies in between 120 and 150 degrees and 30 and 60 degrees.[2]

Irregular astigmatism –      principal meridians are not perpendicular
In With-the-rule astigmatism a minus cylinder is placed in the horizontal axis to correct the refractive error. Adding a minus cylinder in the horizontal axis makes the horizontal axis “steeper” which makes both axes equally “steep.” In Against-the-rule astigmatism a plus cylinder is added in the horizontal axis (or a minus cylinder in the vertical axis).
Children tend to have With-the-rule astigmatism and elderly people tend to have Against-the-rule astigmatism.
Axis is always recorded as an angle in degrees, between 0 and 180 degrees in a counter-clockwise direction. 0 and 180 lie on a horizontal line at the level of the centre of the pupil, and as seen by an observer, 0 lies on the right of both eyes.
Based on focus of the principal meridians
With accommodation relaxed:
Simple astigmatism 
Simple hyperopic astigmatism – first focal       line is on retina while the second is located behind the retina
Simple myopic astigmatism – first focal       line is in front of the retina while the second is on the retina

Compound astigmatism 
Compound hyperopic astigmatism – both focal       lines are located behind the retina
Compound myopic astigmatism – both focal       lines are located in front of the retina

Mixed astigmatism – focal lines are on both      sides of the retina (straddling the retina)

Types of Astigmatism.

Based on axis of the principal meridians

  • Regular astigmatism – principal meridians are perpendicular
    • With-the-rule astigmatism – the vertical meridian is steepest (an American football lying on its side).
    • Against-the-rule astigmatism – the horizontal meridian is steepest (an American football standing on its end).
    • Oblique astigmatism – the steepest curve lies in between 120 and 150 degrees and 30 and 60 degrees.[2]
  • Irregular astigmatism – principal meridians are not perpendicular

In With-the-rule astigmatism a minus cylinder is placed in the horizontal axis to correct the refractive error. Adding a minus cylinder in the horizontal axis makes the horizontal axis “steeper” which makes both axes equally “steep.” In Against-the-rule astigmatism a plus cylinder is added in the horizontal axis (or a minus cylinder in the vertical axis).

Children tend to have With-the-rule astigmatism and elderly people tend to have Against-the-rule astigmatism.

Axis is always recorded as an angle in degrees, between 0 and 180 degrees in a counter-clockwise direction. 0 and 180 lie on a horizontal line at the level of the centre of the pupil, and as seen by an observer, 0 lies on the right of both eyes.

Based on focus of the principal meridians

With accommodation relaxed:

  • Simple astigmatism
    • Simple hyperopic astigmatism – first focal line is on retina while the second is located behind the retina
    • Simple myopic astigmatism – first focal line is in front of the retina while the second is on the retina
  • Compound astigmatism
    • Compound hyperopic astigmatism – both focal lines are located behind the retina
    • Compound myopic astigmatism – both focal lines are located in front of the retina
  • Mixed astigmatism – focal lines are on both sides of the retina (straddling the retina)
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    This is interesting because science and also because the horizontal pic is what I see when I try to read words without...
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    Cool.
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    I have this. I’d tell you which type but I honestly have no idea. It’s hard to tell when you also have a serious case of...
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