Introduction
The pupil is an opening in the center of a muscular diaphragm, the iris. This unique property of the iris musculature to contract and hence shrink their size gives the pupil the characteristic property to widen or constrict in size. This is critical for developing the image quality because it reduces excess light scattering and allows light to be oriented at the same angle as the orientation of our eye's light receptors, known as rods and cones.
The normal size of the pupil is 3 to 4 millimeters in both eyes. A variation of 2 mm between the 2 eyes is considered normal. That means, even if one eye of a patient has a bigger or smaller pupil by 2 mm, it does not necessarily mean that s/he has some ocular problem. The same applies to both eyes.
The process of controlling the size of the pupil is done by nervous control. The arm of the nervous system responsible for this is the autonomous nervous system. This means that the size of our pupils is not in our hands but under autonomic nervous feedback control. The center of this reflex is placed in the Edinger-Westphal nucleus in the midbrain and is relayed through the third cranial nerve and its branches. It is thus implied that any injury or lesions involving the cranial cavity, midbrain, or third nerve will produce pupillary abnormalities.
Is the Pupil a Hole in the Eye?
The pupil's primary function is to constrict and dilate as light rays enter the eye. Deep sleep, high doses, and certain drugs can cause problems with the iris. In the eye, the pupil is a part at the center of the iris (a colored, round structure in the eye). The pupil transfers the light into the brain. It is a black hole in the iris. Iris helps to find the amount of light passing into the eye and maintains the size of the pupil. The pupil becomes smaller when larger light rays are passed through the iris. Smaller light rays pass through the iris and become large.
What Are the Testing Procedures of Pupils?
Testing the pupil is fairly simple and is done using a torchlight, preferably a pen torch. The light causes a constriction of both pupils in a normal patient when shone on one eye. This is because of the shared nervous supply, also known in medical terms as the crossing over of internuncial fibers. The attribute of a brisk and comprehensive contract encompassing the whole of the pupil is considered normal.
These include -
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Drugs - Medications, including certain prescription drugs. For example, cholinergic drugs, as in the case of the abuse of recreational drugs like morphine and other opioids.
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Near Work - During near work, another nervous reflex, accommodation, comes into play and helps us focus on objects and words while reading.
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Emotional Responses - Profound emotions such as crying can cause changes in pupil size, including constriction.
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Ciliospinal Reflex - It is also a nervous reflex. Here, the stimulation of skin over the neck causes pupillary constriction. This is also seen in normal individuals.
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Similarly, diseases causing pupil constriction include injury to the iris, tumors in the brain, and third cranial nerve paralysis commonly. Numerous ocular diseases and ocular inflammation can cause pupillary constriction, such as uveitis. The pupil also undergoes constriction progressively in old age as a process of aging, accompanied by a loss of tissue elasticity.
What Are the Factors That Play a Role in the Dilation of Pupil?
These include -
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Drugs - Atropine, Homatropine, and Phenylephrine.
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Caffeine - Coffee intake in normal individuals.
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Recreational drugs - cocaine.
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Emotional states - This is especially seen in “fight or flight” situations. For example, anger and fear.
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As a normal response to low levels of lighting.
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Similarly, diseases causing dilatation of the pupil include neurological problems such as Adie’s syndrome, Argyll Robertson’s pupil, Horner's syndrome, etc. It can also be seen in injuries to the eyeball and, in particular, the iris.
Problems Seen in Patients with Dilated Pupils:
Although people with constricted pupils have almost no problems with daily activities, the same cannot be said of patients with dilated pupils. As mentioned earlier, the pupil plays an important role in vision by regulating the amount of light entering the eye, thus preventing light scattering and a drop in vision. Therefore, dilated pupils can cause problems like glare and an aversion to bright light (photophobia).
The pulsating pupil is the pressure change between the cerebrospinal fluid and the intraocular space. Repeated dilation and constriction occur in this disorder. Concussed eyes are seen in people with dilated pupils, a sign of blurred vision, and difficulty finding objects in the distance.
What Is the Treatment?
The main treatment mode is the treatment of the underlying causative disease. A visit to the ophthalmologist will facilitate this.
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Good quality sunglasses, preferably with UV (ultraviolet) or Polaroid filters.
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Brimonidine is a prescription medication intended to lower intraocular pressure inside the eye. It has been found to reduce pupil size in several studies.
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Indoor car lighting should be used to reduce the amount of glare while driving at night.
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The physician uses tropicamide to enlarge the hole in the iris and examine the pupils' condition.
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Pilocarpine eye drops constrict the pupil's size when it is damaged.
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Atropine and Phenylephrine drops dilate pupil sizes when they are affected.
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Iridoplasty is performed to mold or change the damaged iris structure using an argon laser. It is retained in its original structure when these procedures are performed.
Conclusion
The human body has no voluntary control or movement in the pupil. Things like using hands and legs for walking, closing eyelids, and people's daily activities are voluntary movements. Although the function of the pupil may be recovered after some treatments, it is not assured that treatment will provide a permanent solution for the pupil's disorder. Performing eye exams at least once a year is important for finding the irregularities and condition of the pupil. Proper management and treatment depend on the severity of the pupil's condition.
