Cycloplegia is paralysis

Paralysis

Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...

 of the ciliary muscle

Ciliary muscle

The ciliary muscle is a ring of striated smooth muscle in the eye's middle layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humour into Schlemm's canal. It changes the shape of the lens within the eye not the size of the pupil which is...

 of the eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

, resulting in a loss of accommodation

Accommodation (eye)

Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image on an object as its distance changes....

.

Anatomy

The iris

Iris (anatomy)

The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...

 is the heavily pigmented colored part of the eye. It has a contractile diaphragm in front of the lens with a central opening called the pupil. It is located between the lens and the cornea, and is attached radially to the ciliary body and the cornea via ligaments called pectinate ligaments.

The iris contains two sets of muscles:

• a radial group for enlargement of the pupil (dilator pupillae)
• a circular group set to decrease pupil size on contraction (sphincter pupillae).

The muscles regulate the amount of light entering the eye. The sphincter pupillae is stimulated through muscarinic receptors by the parasympathetic nervous system. The dilator pupillae is stimulated through noradrenergic receptors by the sympathetic nervous system

Sympathetic nervous system

The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

.

Photophobia

Destruction of the sphincter pupillae from any cause can result in permanent photophobia

Photophobia

Photophobia is a symptom of abnormal intolerance to visual perception of light. As a medical symptom photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of actual physical photosensitivity of the eyes, though the term...

. Light entering an eye with a destroyed sphincter will result in pain, because the pupil can not constrict.

Cycloplegic drugs

Cycloplegic drugs are generally muscarinic receptor blockers. These include atropine

Atropine

Atropine is a naturally occurring tropane alkaloid extracted from deadly nightshade , Jimson weed , mandrake and other plants of the family Solanaceae. It is a secondary metabolite of these plants and serves as a drug with a wide variety of effects...

, cyclopentolate

Cyclopentolate

Cyclopentolate is a mydriatic and cycloplegic agent commonly used during pediatric eye examinations. Cyclopentolate is also administered as an atropine substitute to reverse muscarinic and CNS effects of indirect cholinomimetic administration....

, homatropine

Homatropine

Homatropine is an anticholinergic medication that inhibits muscarinic acetylcholine receptors and thus the parasympathetic nervous system...

, scopolamine

Scopolamine

Scopolamine, also known as levo-duboisine, and hyoscine, is a tropane alkaloid drug with muscarinic antagonist effects. It is among the secondary metabolites of plants from Solanaceae family of plants, such as henbane, jimson weed and Angel's Trumpets , and corkwood...

 and tropicamide

Tropicamide

Tropicamide is an anticholinergic used as a mydriatic. In Russia, it is used to some degree as an inexpensive recreational drug...

. They are indicated for use in cycloplegic refraction (to paralyze the ciliary muscle in order to determine the true refractive error of the lens) and the treatment of uveitis

Uveitis

Uveitis specifically refers to inflammation of the middle layer of the eye, termed the "uvea" but in common usage may refer to any inflammatory process involving the interior of the eye....

. Many cycloplegics are also mydriatic

Mydriasis

Mydriasis is a dilation of the pupil due to disease, trauma or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day...

 (pupil dilating) agents and are used as such during ophthalmoscopic examinations to better visualize the retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

.

When cycloplegic drugs are used to dilate the pupil, the pupil in the normal eye regains its function when the drugs are metabolized or carried away. Some cycloplegic drugs can cause dilation of the pupil for several days. Usually the ones used by ophthalmologists or optometrists wear off in hours, but when the patient leaves the office strong sunglasses are provided for comfort.

See also

• Adie syndrome
  Adie syndrome
  Adie syndrome, sometimes known as Holmes-Adie's syndrome or Adie's Tonic Pupil, is a neurological disorder characterized by a tonically dilated pupil. It is named after the British neurologist William John Adie...
  
  
• Anisocoria
  Anisocoria
  -Causes:In the absence of the iris or eyeball proper, anisocoria is usually the result of a defect in efferent nervous pathways controlling the pupil traveling in the oculomotor nerve or the sympathetic pathways...
  
  
• Marcus Gunn pupil
  Marcus Gunn pupil
  Marcus Gunn pupil is a medical sign observed during the swinging-flashlight test whereupon the patient's pupils constrict less when a bright light is swung from the unaffected eye to the affected eye...
  
  
• Miosis
  Miosis
  Miosis is the constriction of the pupil of the eye to two millimeters or less...
  
  
• Parinaud's syndrome
  Parinaud's syndrome
  Parinaud's Syndrome, also known as dorsal midbrain syndrome is a group of abnormalities of eye movement and pupil dysfunction. It is caused by lesions of the upper brain stem and is named for Henri Parinaud , considered to be the father of French ophthalmology...
  
  
• Syphilis
  Syphilis
  Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...