The human eye is built a bit like a camera, with the main difference that the images “photographed” with it can only be evoked with words. And most often they remain memories for viewing only in the “for your eyes only” mode.
Aperture priority
Contrary to appearances, the pupil is not a black spot, but a transparent hole; an opening that allows a certain amount of light to pass further into the eye and into the retina. When the surroundings are plunged into darkness, the pupil, like the lens of a camera, must collect as much light as possible, so it expands like the aperture of the lens to the maximum. In opposite conditions, when it is bright around, the pupil protects the retina from too strong a beam of light that could damage it, which is why in the sun the pupil is the size of a pinhead. An experiment to confirm this mechanism can be carried out by observing the pupil’s response to different light intensities in a mirror. A healthy pupil, controlled by the muscles of the iris, will react smoothly to changes in light. However, perhaps some will notice a disproportion in their size. The minimal difference in the size of the right and left pupils may be a congenital and physiological feature, but any other case of anisocoria, i.e. pupil unevenness, should be consulted with a doctor: an ophthalmologist or a neurologist.
Marek Żydok, a neurologist who runs a doctor’s office in Chełm, says:
– Anisocory should always be disturbing, although, of course, not in every case it turns out that the cause for anxiety did exist. It may happen that after some time the pupil inequality disappears by itself, but then all the more you have to look for the causes of this condition. I always order computed tomography, depending on the clinical condition of the patient, urgent or delayed.
Why is this seemingly anatomical detail so alarming for a doctor? And what could the pupil have to do with the lung?
The lungs are watching
Well, a lot. Along the entire human spine, on both sides, runs the so-called sympathetic trunk, consisting of ganglia. If the sympathetic innervation of the eye is damaged, a number of symptoms, primarily ophthalmic, can occur, one of which is anisocoria. In addition to her, it is stated, inter alia, drooping eyelid or collapsing eyeball. We are then dealing with Horner’s syndrome, a syndrome of various etiologies. One of the possible causes is lung cancer, which oppresses the sympathetic trunk. The presence of the so-called Pancoast tumor, which is a bronchial cancer located at the top of the lung. Therefore, one of the routes that a doctor diagnosing the causes of anisocoria should follow is the pupil-lung section. The analogy is not obvious, but it is worth keeping in mind.
Unequal pupils can be associated with reactions to certain drugs, such as atropine, or drugs such as cocaine. Anisocoria may be the result of advanced, untreated syphilis, occur in the course of glaucoma or, unfortunately, indicate the development of multiple sclerosis. Some migraine sufferers indicate anisocoria as one of the symptoms of pre-migraine aura.
– The pupil inequality may be a consequence of a head or eye injury – adds Marek Żydok, a neurologist – as well as a remnant of a past infection of the eyeball. However, tomography is necessary because anisocoria can be one of the external manifestations of pathological changes in the brain, including focal changes.
Keep an eye on the pupil
Changes in the appearance and activity of the pupils may be caused by the presence of a developing tumor in the brain that compresses delicate nervous structures and disrupts the proper functioning of the eye. Damage to the oculomotor nerve, the so-called III of the cranial nerve, may cause an aneurysm. Unfortunately, the list of serious neurological threats does not end there, because it also includes meningitis, brain edema, and stroke.
The pupil is also indirectly influenced by viruses and bacteria, as they underlie the development of Adie’s syndrome. This series of neurological symptoms, including anisocoria, is initiated by inflammation in the parasympathetic nervous system.
In diagnostics, apart from the main examination, i.e. computed tomography, it will be important to determine which pupil exhibits pathological features: smaller or larger. This provides the clinician with valuable clues as to where to look for the cause of the pupil unevenness.
Of course, not every anisocory has a dramatic basis, but not every anomaly in the structure and functioning of the brain will manifest in this way. This means that anisokoria must neither be demonized nor taken lightly. You just have to check where it came from.
Text: Julia Wolin
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