What is mydriasis?

The Mydriasis Is a dilation of the pupil that is often produced by non-physiological causes, that is, it is caused by external agents that alter the sympathetic or parasympathetic nervous system, such as certain pathologies and drugs.

The word mydriasis comes from the Greek mydriasis, which joins the adjective mydros ("hot metal / red hot") with the suffix -iasis, which denotes the presence of a disease, as is the case with the word amebiasis.

Mydriasis, therefore, is different from anisocoria (which is the unequal constriction of the pupils) and is the opposite of Miosis . Thus, in mydriasis, pupillary dilation is experienced outside the common in which the iris does not move. In the eye with mydriasis (mydriatic eye), the aperture that gives way to light is extremely widened.

In other words, when a pupil is very dilated it is because it has mydriasis, which may be due to diverse causes that may not always be due to the response of this opening of the eye to light but to health disorders or the action of chemical substances Which were consumed by the person.

However, in all cases mydriasis implies that there was a stimulation of the nervous system which in turn had an impact on the sphincter of the pupil.

The photomotor reflex in the pupil

Source: http://healthool.com/mydriasis/

By photomotor reflex is meant that reflex that naturally occurs when the pupil dilates ("opens") or contracts ("closes"), depending on the amount of light in the room.

In the eye, correct vision allows the constriction of the pupil if the environment is very bright, so that the retina is not damaged by excess light, but also causes the pupil of this pupil to enlarge to capture more light and so Make the vision fit the darkest places.

In the constriction of the pupil, especially if there is miosis, the eye passes through a process in which light penetrates to the retina and then takes a nervous impulse that goes to the brain; From there an order is given so that the sphincter of the pupil is stimulated and closes the hole so that less light enters.

Therefore, the photomotor effect would be no more than the physiological response of the eye to light, which causes that pupillary muscle to become excited and thereby reduce the diameter of that eye opening.

With dilation of the pupil, however, we have an effect in the opposite direction that does not occur as in miosis. As the luminosity is low or zero (that is, there is little light or there is simply no light), the brain does not receive through the eye the stimulus necessary to contract the pupil. As a result, the pupillary sphincter relaxes and makes the opening more open, hence its diameter is greater in both the left eye and the right eye.

A very illustrative comparison of this phenomenon can be made with the camera or, more specifically, with one of its parts: the diaphragm (figure 1). Leaving aside the obvious differences in the structure of human vision and photography, one aspect of the diaphragm is that its degrees of aperture are used to regulate the light that passes through the lens of the lens and reaches the Film, where the image is formed.

By applying an analogy, the camera would have miosis with a small aperture of f / 32 that lets in little light. The amount of illumination increases as the diaphragm opens more and more, with a progressive increase in the orifice diameter, through apertures f / 16, f / 8 and f / 5.6. If the photographer needs his camera to capture more light, he would have to use an aperture of f / 4 or f / 2.8; Already with f / 2 your device would have mydriasis.

As with miosis, mydriasis is also clearly observable by the physician, who can detect if there is any condition or problem that is affecting the person.

Examination of the ocular reaction to light, therefore, has a fundamental value in assessing a patient's health condition, since it is his sight that emits subtle but significant signs indicating that something is not right with The normal physiological functions of your eyes.

Causes of Mydriasis

Source: http://healthool.com/mydriasis/

Previously it was specified that mydriasis has physiological (inherent to biology and visual functions), pathological (directly or indirectly related to diseases, pathologies and other health disorders) and pharmacological causes (strictly related to the use of drugs, substances Of medicinal use and drugs of various kinds).

The following three sections examine these various factors in which the pronounced dilation of the pupils occurs.

Physiological Causes

The physiological causes are those in which the dilation of the pupils occurs as a result of the natural reaction of the eye in the absence or lack of light.

In other words, here the individual has no problem because his pupils dilate just to catch the dim light in the environment in order to better adapt his vision to the dark, and not because there is any disease or chemical that Alter the functioning of your nervous system.

Usually, non-pathological meiosis occurs due to:

• Shortage, absence of light : As explained above, the lack of light stimulus results in a relaxation of the pupillary sphincter. The pupil, therefore, dilates, so that the view is better adapted in an environment that at the moment is dark.
• Oxytocin : A recent 2007 study suggests that increased levels of this hormone are linked to mild to moderate mydriasis. The case analyzed by this investigation was that of a woman who experienced this pupil dilation after sexual arousal. There are still scientific papers under development that will delve into this case.

Pathological causes

[Notice of caution for the reader : If mydriasis is caused by a health problem, consult your doctor to obtain a correct diagnosis that leads to an effective treatment of your condition.

Keep in mind that this section only complies with the duty to inform, so you should not use this article as a substitute for the diagnosis or remedy of your clinical condition, much less as a means to resolve doubts that you should ask a specialist in The matter.]

Pathological causes are those in which pupil dilation occurs due to clinical conditions, conditions, diseases or syndromes in which both the health and quality of life of the patient are at risk.

Therefore, the pupils do not have a normal reaction to the light, because if so, they would shrink to protect the integrity of the retina and also to optimize the vision of the affected person. Some of these problems are:

• Paralysis or damage to the parasympathetic nerve : Occurs in the cranial nerve III, directly responsible for miosis. When this nerve is affected for some reason, the pupil can not contract because the sphincter stops working.
• Disorders of the central nervous system : The ocular nerves can be seriously compromised before diverse affections, such as the Stroke , Cerebral hernia, sudden increase in brain mass and epilepsy .
• Cranioencephalic injuries : these Affections Damage the nerves and eye muscles. In general it refers to blows, fractures, contusions and hemorrhages that are located in the head. Very common in traffic accidents and in combat sports such as boxing, in which an injury to the orbit of the eye prevents the pupils from contracting, so that they do not react to light.

Pharmacological causes

The pharmacological causes are those in which the dilation of the pupils can happen through chemical reactions that are proper of the consumption of substances that take part in the performance of the neurotransmitters in the brain.

Here the person took drugs or drugs of some sort that Altered the functioning of your nervous system , So your eyesight has irregularities in reacting to the stimulus of light. Some of these factors are:

• Poisoning Of different nature.
• Drugs : Anticholinergics, atropine, ephedrine, hyoscyamine, Scopolamine (Also known as burundanga) and alkaloids present in solanaceae, such as belladonna ( Atropa belladonna ). These substances block the brain chemistry that is responsible for the constriction of the pupil.
• Stimulants and antidepressants : Apart from various supplements, drugs such as cocaine and the Amphetamines Raise the levels of Serotonin And end up causing dilation of the pupils.
• Mydriatic Agents : Drugs and drugs that dilate the pupils (that is, cause mydriasis), but for medical purposes, such as tropicamide and cyclomidril.

References

1. Alemañy Martorell, Jaime and Villar Valdés, Rosendo (1983). Ophthalmology (4th ed., 2003). Havana Cuba. Editorial Medical Sciences.
2. Ball, Jane W., Stewart, Rosalin W. et al (1987). Mosby's Guide to Physical Examination (7th ed., 2011). Missouri, United States. Mosby.
3. Cyclomydril [Online article] (2017). Auckland, New Zealand. Drugs.com. Accessed January 28, 2017, on drugs.com.
4. Medical-biological dictionary, historical and etymological. Mydriasis (2014). Salamanca, Spain. University of Salamanca.
5. Galán Terraza, Alicia (2011, October 14). The photomotor reflex or why the pupil closes with the light [Online article]. Barcelona, ​​Spain. DYTO ophthalmic clinic. Accessed January 27. Llano Sosa, David S. del, and Ramírez Velázquez, Reyvis (2009). Ophthalmological terminology. Bilingual glossary. Spanish-English / English-Spanish. Havana Cuba. Editorial Medical Sciences.
6. Millodot, Michel (1986). Dictionary of Optometry and Visual Science (7th ed., 2014). Amsterdam, The Netherlands. Elsevier Health Sciences.
7. Ritch, R.; Dorairaj, J. M. and Liebmann, J.M. (2007, February 16),"Angle-closure triggered by orgasm: a new provocative test?". Eye, 21 (6), pp. 872-874. Available on nature.com.
8. Traumatic Mydriasis and Miosis [Online article] (2016). San Francisco, United States. American Academy of Ophthalmology. Accessed January 27, 2017.
9. Tropicamide [Online article] (2017). Auckland, New Zealand. Drugs.com [Website]. Accessed January 28, 2017, on drugs.com.
10. Ceballos Torres, Juan Carlos (2013, November 2). Ocular changes in sexual relations [Online article]. Madrid Spain. Optics by Face [Website]. Accessed January 28, 2017, at opticaporlacara.com.
11. González García, Antonio (2011). Analogic photograph. Initiation. The camera. Camera Controls [Online Article]. Sevilla Spain. Sevilla University. Consulted the 27 of January of 2017, in hosped.us.es.