Technological advancements have made the automated pupillometer a significant tool in the critical care of severe TBI patients

 

Pupils


During the initial inspection, it's crucial to keep a close eye on the pupil size and responsiveness to light. The parasympathetic axons are impaired by compression of the oculomotor nerve, which can indicate temporal lobe/uncal herniation and result in modest pupillary dilation and a sluggish pupillary light response.Bilateral miotic pupils (1–3 mm) can also arise in the early stages of herniation due to a breakdown of the hypothalamic pupillomotor sympathetic pathways, allowing parasympathetic tone and pupillary constriction to predominate. The pupil dilates and the light response becomes paralysed as the herniation progresses. Ptosis and paresis of the medial rectus and other ocular muscles innervated by the oculomotor nerve manifest with full mydriasis (8 to 9 mm pupil). To determine pupillary light responses, a bright light in a darkened area is always required. 

Clinical trials of computerised pupillometry were conducted in the past, with initially mixed results.78 However, technological advancements have made the automated pupillometer a significant tool in the critical care of severe TBI patients. The use of an automated pupillometer in critical care populations was associated with enhanced reliability in the assessment of a patient's pupillary response, according to a direct comparison of automated pupillometry to standard clinical practise.

Even with small pupils (less than 2 mm), current automated pupillometers can assess both pupillary size and responsiveness. To improve intraobserver reliability, automated pupillary systems should be considered in any critical care situation. 79

In the evaluation of the patient with h, it is helpful to recognise further pupillary problems that can arise in an unconscious patient with head trauma.

The swinging flashlight test detects disruption of the afferent arc of the pupillary light reflex within the optic nerve.



Another option is to use a corneal reflection pupillometer.

Monocular PDs can be assessed more precisely using pupillometers than with an anatomical measurement (Holland & Siderov 1999).This is useful when ordering spectacles for severe refractive errors or progressive addition lenses, as each lens must be precisely centred along the patient's visual axes. Furthermore, the operation is quick and straightforward, and it may be done by a clinical assistant without the use of binoculars.

A corneal reflection pupillometer's PD will normally be 0.5–1 mm less than the anatomical PD (Holland & Siderov 1999, Osuobeni & Al-Fahdi 1994). This is because pupillometers assess the ‘physiological PD,' or the distance between the two main corneal reflexes, and locate the visual axis, whereas anatomical PD determines the lines of sight or optical axes. Many pupillometers have a correction for the parallax inaccuracy discussed in the anatomical PD section (Brown 1991). 

If the pupillometer is placed higher or (typically) lower on the bridge than the desired spectacle frame, and the nose is not straight, the monocular PDs can be displaced to one side, causing inaccuracies.

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