Detecting Abnormalities and Pupillary Disorders with Pupil Size

Pupillary Disorders | Ento Key

The principles of neuro-foundational ophthalmology, as well as pupillary size measurement, are dependent on an understanding of pupillary reactions. Professionals must cultivate this skill in emergencies, clinics, and, most importantly, exams. To begin, the pupil is the primary aperture of the iris, which regulates the amount of light that reaches the retina. Its diameter ranges from around 1 to 8 mm in diameter, depending on the species of the eye.

When the sympathetic and parasympathetic nervous systems engage, this causes the interaction that leads to pupil size. The only way to make a valid diagnosis during a clinical examination is to examine the pupils and pupillary reflexes.

Normal pupil reflexes

Pupil constriction

The activation of the parasympathetic nervous system forces the pupillary muscles to contract, which causes pupillary light reflex. As a result of two inputs, it is a normal response: light falling on retinal photoreceptors and the effort required for completing near reflexes and accommodation.

Pupillary light reflex

Four kinds of neurons are involved in the constriction of the pupil in response to light. It originates in the retina’s ganglion cell layer, where it gives rise to the optic nerves and continues to the brain through the afferent pathway. The fibers escape the optic chiasm in the pretectal nucleus and proceed to both optic tracts. Internuncial neurons link each pretectal nucleus on either side of the brain to the ipsilateral Edinger-Westphal nucleus. The contralateral Edinger-Westphal nucleus may be reached through the posterior commissure on the other side of the brain.

Indirect and direct pupil reactivity is possible because both Edinger-Westphal nuclei receive input from the same optic nerve. It is via the inferior oblique branch that preganglionic parasympathetic fibers enter, leave the nerve, and connect to the ciliary nerve. Sphincter pupillae is fed by post-ganglionic fibers that go via the short ciliary nerves and into the iris.

Accommodation

To get to the occipital lobe, afferent limbs of the reflex pass from the retina to the lateral geniculate body. Midbrain fibers stimulate the Edinger-Westphal nucleus and vergence cells of the reticular formation located in the occipital region. Even if you are visually impaired, there are ways to make things easier.

 

The Edinger-Westphal nuclei in pre-striate cortex region 19 may be stimulated bilaterally to get the same outcomes. A reduction in globularity and an increase in refractive power are two reactions to this stimulation. The third response is a contraction of the ciliary muscles and relaxation of the zonules, increasing the lens’s refractive power. The sphincter pupillae constrict simultaneously, preventing light from passing through the lens’s periphery section. The intensity of the reticuli causes the eyes to become more focused on the same topic, which is essential in the measurement of pupillary acuity.

Pupil dilation

It’s also possible that the pupils dilate due to sympathetic activity. Innervation in the posterior hypothalamus nucleus is related to sympathetic nerve roots that exit the spinal cord, making this pathway critical.

This neuron originates from the first thoracic nerve root to join the paravertebral sympathetic chain, which goes to the superior cervical ganglion. Carotid arteries, both exterior and internal, are coated with post-ganglionic fibers. After traveling via the long ciliary nerve, a part of the sympathetic fibers enters the trigeminal nerve ophthalmic division in the cavernous sinus and supplies the dilation pupillae there.

There are face sweat glands and eyelid muscles supplied by this pathway. Pupils dilate in response to stress, anxiety, or fear, and these factors are considered during pupil measurement.

Pupil reactivity eye disorders

Adie’s tonic pupil

It is known as Adie’s tonic pupil because it has a huge pupil that does not contract in reaction to light but instead contracts gradually in response to accommodation and pupil reactivity.

“Light-near dissociation” is the term used to describe the pupillary response in traumatic brain injury. A gradual constriction and re-dilation to distance are normal after persistent close exercise. The parasympathetic nervous system has been harmed due to post-ganglionic fiber damage. For 90 percent of the population, it begins as a unilateral disorder before spreading to both sides of the spectrum.

This condition referred to as “little old Adie’s pupil,” ultimately progresses to the point where it is tonic and even miotic. Female genital herpes is a common illness that affects both men and women in the genital area. However, it is frequently caused by an idiopathic cause such as a viral infection, diabetes, or a traumatic event. It is known as Holmes Adie syndrome, and it is a condition in which the reflexes of the tendons begin to fail. While an average pupil will not be altered by denervation hypersensitivity to moderate cholinergic drugs (0.125 percent pilocarpine), an abnormal pupil will be affected.

Acute angle-closure glaucoma 

Because of the peripheral iris crowding during semi-dilation, the anterior chamber angle is mechanically closed after the pupil has been semi-dilated. A tumor might cause this syndrome in the eye, creating anterior or posterior synechiae after uveitis or rubeotic glaucoma induced by fibrovascular development in the chamber angle caused by retinal ischemia (diabetes and central retinal vein occlusion classically). The use of a slit-lamp evaluation of pupillary reaction will be necessary to confirm the diagnosis if the patient’s narrative alone does not show the existence of an ocular emergency. If a patient develops this condition, the ophthalmologist should be alerted as soon as possible, preferably immediately. For these individuals, glaucoma drops, intraocular pressure-lowering medications, topical miotics, and iridotomy may be beneficial in reducing the amount of pressure in their eyes during the pupil measurement.

Third nerve palsy

Complete and partial third-nerve palsy are the two forms of third-nerve palsy that may occur. In the affected eye, three-nerve palsy expresses itself as a completely dilatable pupil, a ‘down and out’ eye, ptosis, and the lack of light or accommodation constrictions. To determine the existence of an efferent route, shine an intense light into the affected eye and see if the pupil dilates or does not dilate. However, this has not affected the consensual light response in the opposing eye. Compressive lesions (aneurysms, tumors, and trauma), hypertension, and diabetes are only a few of the factors that might cause a microvascular infarction (occlusion of the vasa nervorum). 

The fact that modest third-nerve palsy symptoms are slight does not rule out the possibility that they indicate the need for prompt medical intervention. Because of the rapid rise in intracranial pressure, the third nerve is often pinched against the crest of the petrous temporal bone, causing it to become inflamed. Parasympathetic fibers, which are located close to the skin’s surface, become inflamed, resulting in dilated pupils on the side of the body that the inflammation has impacted. It is virtually always necessary to do a CT angiography to screen for intracranial aneurysms when there is an immediate need for surgical decompression of the brain as a consequence of pupillary dilation.