The effect of this will be that when a vertical beam of light in the distance travels towards the eye, the "minus" cylinder (which is placed with its axis lying horizontally – meaning in line with the patients horizontal meridian relative to the excessively steep vertical meridian) will cause this vertical beam of light to slightly "diverge", or "spread out vertically", before it reaches the eye. This compensates for the fact that the patients eye converges light more powerfully in the vertical meridian than the horizontal meridian. Hopefully, after this, the eye will focus all light on the same location at the retina, and the patients vision will be less blurred.In against-the-rule astigmatism, a plus cylinder is added in the horizontal axis (or a minus cylinder in the vertical axis).Axis is always recorded as an angle in degrees, between 0 and 180 degrees in a counter-clockwise direction. Both 0 and 180 degrees lie on a horizontal line at the level of the center of the pupil, and as seen by an observer, 0 lies on the right of both the eyes.Irregular astigmatism, which is often associated with prior ocular surgery or trauma, is also a common naturally occurring condition. The two steep hemimeridians of the cornea, 180° apart in regular astigmatism, may be separated by less than 180° in irregular astigmatism (called nonorthogonal irregular astigmatism); and/or the two steep hemimeridians may be asymmetrically steep—that is, one may be significantly steeper than the other (called asymmetric irregular astigmatism).
Causes
The most common cause is the mismanagement of 3rd stage of labor, such as:

Fundal pressure
Excess cord traction during the 3rd stage of laborOther natural causes can be:

Uterine weakness, congenital or not
Precipitate delivery
Short umbilical cordIt is more common in multiple gestation than in singleton pregnancies. Associations
Placenta praevia
Fundal Placental Implantation
Use of Magnesium Sulfate
Vigorous fundal pressure
Repeated cord traction
short umbilical cord

Types
One: Complete. Visible outside the cervix. Two: Incomplete. Visible only at the cervix. Treatment
Treatment involves standard resuscitation together with replacing the uterus as rapidly as possible. If efforts at manual replacement are not successful surgery is required. After the uterus is replaced oxytocin and antibiotics are typically recommended. The placenta can then be removed if it is still attached. Epidemiology
Uterine inversion occurs in about 1 in 2,000 to 1 in 10,000 deliveries. Rates are higher in the developing world. == References ==