Another recent follow-up study again had identified four novel loci for corneal astigmatism, with two also being novel loci for astigmatism: ZC3H11B (associated with axial length), NPLOC4 (associated with myopia), LINC00340 (associated with spherical equivalent refractive error) and HERC2 (associated with eye color). Acquired
Astigmatism may also occur following a cataract surgery or a corneal injury. Contraction of the scar due to wound or cataract extraction causes astigmatism due to flattening of the cornea in one direction. In keratoconus, progressive thinning and steepening of the cornea cause irregular astigmatism. Pathophysiology
Axis of the principal meridian
Regular astigmatism – principal meridians are perpendicular. (The steepest and flattest meridians of the eye are called principal meridians.) With-the-rule astigmatism – the vertical meridian is steepest (a rugby ball or American football lying on its side). Against-the-rule astigmatism – the horizontal meridian is steepest (a rugby ball or American football standing on its end). Oblique astigmatism – the steepest curve lies in between 120 and 150 degrees and 30 and 60 degrees. Irregular astigmatism – principal meridians are not perpendicular.In with-the-rule astigmatism, the eye has too much "plus" cylinder in the horizontal axis relative to the vertical axis (i.e., the eye is too "steep" along the vertical meridian relative to the horizontal meridian). Vertical beams of light focus in front (anterior) to horizontal beams of light, in the eye. This problem may be corrected using spectacles which have a "minus" cylinder placed on this horizontal axis.
Epinephrine, also known as adrenaline, is a medication and hormone. As a medication, it is used to treat several conditions, including anaphylaxis, cardiac arrest, asthma, and superficial bleeding. Inhaled epinephrine may be used to improve the symptoms of croup. It may also be used for asthma when other treatments are not effective. It is given intravenously, by injection into a muscle, by inhalation, or by injection just under the skin.Common side effects include shakiness, anxiety, and sweating. A fast heart rate and high blood pressure may occur. Occasionally, it may result in an abnormal heart rhythm. While the safety of its use during pregnancy and breastfeeding is unclear, the benefits to the mother must be taken into account.Epinephrine is normally produced by both the adrenal glands and a small number of neurons in the brain, where it acts as a neurotransmitter. It plays an essential role in the fight-or-flight response by increasing blood flow to muscles, heart output, pupil dilation, and blood sugar. Epinephrine does this through its effects on alpha and beta receptors. It is found in many animals and some single-celled organisms, but the medication is produced synthetically and is not harvested from animals.Jōkichi Takamine first isolated epinephrine in 1901, and it came into medical use in 1905. It is on the World Health Organizations List of Essential Medicines. It is available as a generic medication. In 2017, it was the 263rd most commonly prescribed medication in the United States, with more than one million prescriptions.