Pupil diameter measurement should be part of every comprehensive eye exam, as that could reveal serious retinal and neuro-ophthalmic conditions. For the diagnosis of pupillary response in traumatic brain injury and the management of these illnesses at the primary care level, the use of this test may be helpful. This article explains the most common pupil abnormalities and how physicians may discover them via frequent pupil testing.
Anatomy of the pupillary system
Understanding the pupillary light response architecture and the autonomic innervation of pupil reactivity is critical for the accurate interpretation of pupillary data. Parasympathetic nerves control the pupillary light reflex and rapid responses to stimuli. Either the afferent or the efferent pathway contributes to the pupillary light response. Retinal photoreceptors transfer light to the optic nerve, which travels to the optic tract and chiasm slightly anterior to the lateral geniculate body (LGN).
It is separated from the tract and travels to the midbrain, where it is projected to both pretectal nuclei bilaterally. Transmissions from pretectal nuclei are made through efferent pathways. There are two Edinger-Westphal nuclei in CN III, and they serve as the beginning point of the efferent route. Midbrain pretectal nuclei and the two Edinger-Westphal nuclei of the oculomotor nerve (CN III) are connected to the efferent pathway via pupil fibers.
Measure Pupil Size
If you have a doctor measure pupil size and analyze direct and consensual light reactions arising from this neuroanatomy, you may objectively assess its integrity. For example, suppose that the right eye answers immediately (and the left eye responds consensually). So, for example, the right afferent pathway is functioning properly. Consequently, the pupil does not expand in either eye when there is a lesion in the optic nerve or the optical tract. Once in orbit, efferent pupil fibers travel back to the eyeball with CN III, where they synapse in the ciliary ganglion, with only 3% of post-ganglionic fibers innervating the iris sphincter muscle (which allows for miosis) and the remaining 97% innervating the ciliary body (which regulates blinking) (which allows for accommodation).
To provide sensory input to the eye, the oculo-sympathetic nerve has three neurons. In the posterior hypothalamus, the first-order neuron is generated. The ciliospinal center of Budge is located between the levels of the eighth cervical. And fourth thoracic vertebrae of the brainstem (C8-T4). On its way out of your spinal cord, a second-order neuron connects with your lungs’ apex and then connects to your superior cervical ganglion. To get to the eye, post-ganglionic axons travel down the internal carotid artery and through the cavernous sinus to the ophthalmic division of the trigeminal nerve (V1) and the ophthalmic artery. For V1, neurons continue to innervate the iris dilation muscle, which is responsible for mydriasis, while in V2, neurons continue to innervate Mueller’s muscle, which is responsible for eyelid control.
The Swinging Flashlight Test
Testing for afferent pupillary abnormalities with a portable penlight or a swinging flashlight is preferable because of the higher light intensity. When detecting afferent pupillary abnormalities, clinicians should use a transilluminator or the light from a binocular indirect ophthalmoscope instead of a portable penlight. The direct pupillary reaction and the consensual pupillary response are measured in the same eye.
A patient with a relative afferent pupillary deficit (RAPD), also known as an APD or Marcus Gunn pupil, suggests damage at or anterior to the lateral gaze nucleus when the consensual response in the affected eye is bigger than the direct response in the other eye (LGN). An RAPD may only be induced if the injury to the retina, optic nerve, or a lesion behind the eye is either unilateral or asymmetrical.
An extreme but bilaterally equal situation can’t lead to a RAP since there is no bilateral APD. Ocular media or refractive errors can’t even cause an RAPD in extreme circumstances. Doctors should always seek an RAPD if one eye is substantially impair in visual acuity. However, it is not always the case that this is the case.
Evaluation of the Size and Shape of Pupils
There should be no misalignment of the iris or pupil. The iris sphincter controls pupil size and the amount of light passing through the eye; therefore, sympathetic innervation (iris dilator) is less powerful in limiting the amount of light passing through the pupil.
Variations in light and eyeglasses might cause a patient’s pupil to change size. Pupil evaluation should begin with measuring the patient’s pupil diameter to see whether there is any evidence of anisocoria. As one age, the pupil’s diameter reduces owing to senile miosis, which occurs in the later years of life. At least a 0.4mm disparity between the two eyes is consider clinically significant. As the name implies, just one of the patient’s eyes is afflict by anisocoria. Physiologic, pharmacologic, or pathological causes are all possible.
The sympathetic and parasympathetic channels should be separate in future studies of anisocoria by reassessing pupil size in bright and dim light. If the difference in pupil diameters is greater under bright light, parasympathetic denervation has occurred. Sympathetic innervation is abnormal if the difference in pupil size is greater under low conditions.
It is important to adequately record patients who have recently been expose to medications or chemicals. That might cause an increase in pupil size, as well as those. Who have recently had a traumatic or surgical event. An old image or the patient’s driver’s license might help physicians understand how long an illness has been going on.
If the anisocoria is physiologic in origin, all lighting conditions should be the same. Eyes may switch throughout the day and have little more than 1 mm of physiologic anisocoria. In the case of physiologic anisocoria, no further pharmacological evaluation is require. In the meantime, physicians should rule out any other possible neurological conditions.
A pupil evaluation and pharmacological testing may be use to determine. The existence of either sympathetic or parasympathetic anomalies in the autonomic nervous system. Even if patients and co-managing practitioners are unaware that they have a neurological condition. They may benefit from the observations and tests of an OD.