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\begin{document}

\title{Pupil Size and Reactivity in Pediatric Patients with Sickle Cell Disease}



\author[1]{Joana Mack}%
\author[2]{Sara Frankowski}%
\author[2]{Bethany Verkamp}%
\author[2]{Shelley Crary}%
\author[3]{Beverly Spray}%
\author[1]{Lee Crawley}%
\author[2]{Suzanne Saccente}%
\author[4]{Kathleen Neville}%
\affil[1]{Arkansas Children's Hospital}%
\affil[2]{University of Arkansas for Medical Sciences}%
\affil[3]{Arkansas Children's Research Institute}%
\affil[4]{University of Arkansas System}%


\vspace{-1em}



  
  \date{May 25, 2024}


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\selectlanguage{english}
\begin{abstract}
Background/Objectives: Pupil size and reactivity have been studied in
adult and pediatric populations to objectively measure pain which showed
that pupillometry is a promising biomarker for pain measurement.
Vaso-occlusive crisis, is a common complication of sickle cell disease
(SCD) and better assessment tools are needed. The objective of this
study is to establish normative values for pupil size and reactivity in
pediatric patients with SCD with the hope that pupillometry can be used
as a tool to objectively measure pain and response to treatment.
Design/Methods: Institutional review board (IRB) approved prospective
study enrolled 82 patients with SCD. Readings were performed using a
NeurOptics PLR-2000 pupillometer. The following measures were collected:
resting pupil size, \% change in pupil size, pupil constriction
velocity, and pupil dilation velocity. Results: Forty-four males and 38
females, all black, were studied. Median age was 11 years (range:2-21).
The mean minimum and maximum pupil sizes were 3.52mm and 5.08mm,
respectively. The mean dilation velocity and maximum constriction
velocity were 1.03mm/s and -4.48mm/s, respectively. When comparing our
participants with white participants in a previously published pediatric
study, there was a significant difference in maximum constriction
velocity, maximum pupil size, and minimum pupil size.1 There was no
significant difference when comparing means for these parameters.
Conclusion: There was no significant difference in pupil size and
reactivity between patients with SCD and black patients without the
disease. Further investigation of pupillometry within the black
population during vaso-occlusive crisis and in the ``well state'' is
warranted in pediatric patients with SCD.%
\end{abstract}%



\sloppy


\textbf{Introduction}

Pupil size and reactivity have been studied in the adult and pediatric
populations in an attempt to objectively quantify pain. Previously
conducted studies have demonstrated pupillometry as a promising
biomarker for objective pain measurement.\textsuperscript{1-3} A 2012
study demonstrated the significant correlation between patient verbally
reported pain and pupillary dynamics in order to guide narcotic
administration.\textsuperscript{2} Another study showed that
pupillometry is a more sensitive test for pain assessment and response
to medication than other hemodynamic markers, including vital
signs.\textsuperscript{3} Factors including patient age, sex, and
ethnicity have been previously studied in order to better understand the
potential variables affecting pupil dynamics and establish a set of
normal values. Regarding pupillary dynamics in younger patients, Brown
et al. evaluated the pediatric population and demonstrated a slight
change in pupil dynamics across pediatric age groups as well as
differences across various ethnicities.\textsuperscript{1}

Pupillometry is conducted using a hand-held device that measures a
variety of pupil dynamics following exposure to an infrared light
stimulus. The parameters of pupil constriction and dilation velocity as
well as minimum and maximum pupil sizes are the most significant
categories used for comparison of patient populations. The testing is
noninvasive, quick, and carries little to no risk for the patient,
making pupillometry an ideal tool for pain measurement.

The clinical application of pupillometry is particularly useful in the
young pediatric population as it is more difficult to understand
subjective patient-reported pain, and an objective pain evaluation
measurement is needed. For example, in the pediatric sickle cell disease
population, vaso-occlusive crisis is a common complication that presents
with acute pain. Vaso-occlusive pain crises are often over or
undertreated due to fear of medication side-effects, possible addiction,
and variable tolerance.\textsuperscript{4} Quantifying acute pain and
response to treatment has been difficult due to dependence on subjective
measures. In this study, we aim to measure pupillometry measurements in
pediatric patients with sickle cell disease as a first step to establish
normative data for future utilization in cases of acute pediatric
vaso-occlusive pain crisis.\textsuperscript{1}

\textbf{Methods}

The University of Arkansas for Medical Sciences (UAMS) IRB approved this
prospective, single-center study. Male and female patients ages 2-21
years were approached at Arkansas Children's Hospital Sickle Cell clinic
during their outpatient visits. Patients with sickle cell disease (SS,
SC, SB\selectlanguage{ngerman}º-thalassemia, SB\textsuperscript{+}-thalassemia) were considered
for the study and screened for enrollment. Patients were eligible if
they were afebrile for 48 hours (fever defined as temperature
\textgreater{}101°F), had vital signs within normal limits, had not
received any narcotics in the last 24 hours, and were not currently
experiencing any pain based on a patient-reported, age-appropriate pain
scale. Additionally, patients were excluded if they had a prior history
of stroke or neurological deficits.

After consent was obtained, each child was tested using the NeurOptics
PLR-2000 Pupillometer. The handheld device includes a rubber cup that is
placed over the child's eye in order to block any outside light sources.
The device then locates the pupil and measures the resting (maximum)
pupil diameter (mm). Next, an infrared light briefly flashes and the
pupillometer measures the average and maximum pupil constriction
velocity (mm/s), minimum pupil diameter (mm), \% change in pupil size in
response to light, and the pupil dilation velocity after exposure to
infrared light stimulus (mm/s) (Fig. 1). The testing takes \textless{}2
minutes, is noninvasive, and is associated with little to no risk for
the patient. Patient data was excluded if a reading could not be
obtained after 4 measurement attempts.

After data collection, the measurements were divided across different
age groups as well as male vs. female study participants for analysis.
Maximum and minimum pupil sizes were reported as means with standard
deviations across six age groups (range 2-21 years old). Maximum and
minimum pupil sizes, maximum and average constriction velocity, and
dilation velocity were reported as means with standard deviation and p
values as overall, male, and female results.

Data were evaluated for assumptions of normality and equal variances
using the Shapiro--Wilk~W test~and Levene's tests, respectively. To
determine if pupillometry measures differed between gender, independent
sample t-tests were conducted. Minimum and maximum pupil sizes were
presented as means and standard deviations. The GPLOT procedure,
incorporating linear regression, was utilized to create scatter plots
and regression lines for pupil size and velocity by patient age. All
data were analyzed using SAS software version 9.4 (SAS Institute, Cary,
NC, USA).

\textbf{Results}

A total of 82 participants, 44 males and 38 females, enrolled in the
study. All study participants were black with a median age of 11 years
old (range 2-21). In order to analyze the data for potential
differences, measurements were extrapolated and compared between age
groups and biological sex. The summary of all measured pupil dynamics
and corresponding mean values with reported p-values can be seen in
Table 1. The overall mean minimum and maximum pupil sizes were 3.52mm
and 5.08mm, respectively. There was no statistically significant
correlation in minimum and maximum pupil size with age (Fig. 2). The
mean dilation velocity and maximum constriction velocity were 1.03mm/s
and -4.48mm/s, respectively. No statistical significant correlation was
found between dilation velocity, maximum constriction velocity and age
(Fig. 2). There was no statistically significant difference between
males and females for all pupil dynamics. A breakdown of participant
ages and corresponding mean maximum and minimum pupil sizes can be seen
in Table 2.

The Brown et al. study reported a mean maximum constriction velocity of
-4.42mm/s, mean maximum pupil size of 4.97mm, and mean minimum pupil
size of 3.4mm for their healthy black participants revealing no
significant difference compared to our means (t = 0.46; p = 0.645), (t=
1.25, p = 0.216), (t = 1.84, p = 0.069), respectively. However,
comparing our participants with their white participants, there was a
significant difference in maximum constriction velocity (t = 3.45; p =
0.009), maximum pupil size (t = -5.57mm, p \textless{} 0.00001), and
minimum pupil size (t = -3.24, p = 0.002).

\textbf{Discussion}

The use of pupillometry as an objective method to measure pain and
analgesic response has proven to be a useful modality in a variety of
populations; however, establishing normative values for select
populations is still evolving as variables such as age, ethnicity, or
certain comorbidities have shown variability in comparative
measurements.\textsuperscript{1-3} This study suggests that when using
pupillometry as a clinical tool in pediatric patients with sickle cell
disease, it is reasonable to use the normative values established in
previous studies of healthy participants with similar age and race.

Previous studies have shown significant differences in measurements when
comparing age groups of healthy participants. With age, pupil size and
dilation velocity increase slightly while maximum constriction velocity
decreases. These changes with age are fairly correlated with changes in
eye size but may also be influenced by developmental changes of the
pupillary reflex.\textsuperscript{1,5} In the study by Brown et al.,
there were also significant differences in pupil size and maximum
constriction velocity when comparing healthy black to their respective
white cohorts. Our results also reflect a variation amongst races as our
data showed no significant change when comparing children with sickle
cell disease to healthy black children of a similar age, but did show a
significant difference amongst our participants in contrast to their
white cohorts in the aforementioned study.

When comparing various comorbidities to baseline values obtained from
healthy participants of similar age and race, some disease processes
have reflected significant changes, making it difficult to use
previously established normative values for those specific populations.
For example, children with ADHD have been shown to have higher pupillary
velocity values in correlation with changes in thickness of the retinal
nerve fiber layer and anxiety has been correlated with increased pupil
sizes.\textsuperscript{6,7} Specific disease processes affecting the
retina, such as diabetic retinopathy, have expectedly shown progressive
changes in pupillary dynamics with increasing disease
severity.\textsuperscript{8} Given the lack of a significant difference
in our data when contrasted with Brown et al.'s black participants, our
study supports the use of previously established normative values when
using pupillometry in the assessment of children with sickle cell
disease, as it does not appear to influence pupil dynamics.

Our data was obtained during outpatient clinic visits when participants
were presumed to be at their baseline state of health and without
significant pain or recent opioid use. This was done to first ensure
that sickle cell disease did not lead to baseline changes in pupil
dynamics prior to future investigations regarding changes during an
acute vaso-occlusive pain crisis and its associated management with
narcotics.

Vaso-occlusive crisis is unique to the sickle cell and is a major
contributor to disease morbidity that is often difficult to treat
appropriately. These crises are characterized by nociceptive pain and
associated inflammation which can lead to severe sequelae such as
multiorgan failure and even death.\textsuperscript{9} Opioids are a
cornerstone of treatment during an acute pain crisis, but the assessment
of pain and treatment efficacy is challenging as current measurements
rely on subjective measurements that are not all encompassing and
difficult for younger or non-verbal children to utilize. Due to concern
of inadequate pain treatment and concern for adverse effects of opioids,
pain is often under or over treated, hence the need for a reliable,
objective method of pain measurement in this
population.\textsuperscript{9}

In a recent study by Connelly et al. self-reported pain levels in
healthy children undergoing surgical procedures showed significant
associations with several measures of pupillary response. Amongst these
measures, maximum pupillary constriction velocity, a dynamic measurement
of pupil response to a light stimulus, showed the most promise as a
surrogate marker of pain. Their data showed an increase of 2 or more on
the validated visual analog scale (VAS) was associated with a change of
\selectlanguage{english}[?] 0.22mm/sec in maximum constriction velocity. As expected, an
association between drug dose (in morphine equivalents) and pupil size
was observed; however, when controlled for opioid effect, an independent
effect of pain on pupil response persisted.\textsuperscript{10} Despite
the known effect of opioids on pupil size, changes in dynamic pupil
parameters have continued to be observed following titration of opioid
dose to a level that elicits respiratory depression, and
intraoperatively, changes in pupillary reflex dilation in children have
occurred prior to significant changes in heart rate or blood pressure,
suggesting that pupillometry could be a valid tool in not just initial
assessment of pain level, but also when evaluating analgesic
response.\textsuperscript{11,12}

Patients with a history of stroke or other neurological deficits were
not included therefore normative values found in this study cannot be
extended to that particular population. Another limitation to this study
was that every patient was black. As the population become more
interracial, there needs to be further studies looking at their specific
normative pupillometry values.

In conclusion, black pediatric patients with sickle cell disease have no
significant difference in pupil size and reactivity compared to black
pediatric patients without sickle cell disease but have a significant
difference compared to white participants in the Brown et al study.
Pupillometry studies are needed in pediatric patients with sickle cell
disease in an acute vaso-occlusive crisis and are currently in progress
at our institution.

\textbf{Conflict of Interest}

The authors declare that there is no conflict of interest.

\textbf{Acknowledgements}

Thank you to patients who participated in this study.

\textbf{Data Availability Statement}

The data that support the findings of this study are available on
request from the corresponding author. The data are not publicly
available due to privacy or ethical restrictions.

\textbf{References}

1. Brown JT, Connelly M, Nickols C, Neville KA. Developmental Changes of
Normal Pupil Size and Reactivity in Children. \emph{J Pediatr Ophthalmol
Strabismus} . 2015;52(3):147-151. doi:10.3928/01913913-20150317-11

2. Aissou M, Snauwaert A, Dupuis C, Atchabahian A, Aubrun F, Beaussier
M. Objective Assessment of the Immediate Postoperative Analgesia Using
Pupillary Reflex Measurement: A Prospective and Observational
Study.\emph{Anesthesiology} . 2012;116(5):1006-1012.
doi:10.1097/ALN.0b013e318251d1fb

3. Barvais L, Engelman E, Eba JM, Coussaert E, Cantraine F, Kenny GN.
Effect site concentrations of remifentanil and pupil response to noxious
stimulation. \emph{British Journal of Anaesthesia} . 2003;91(3):347-352.
doi:10.1093/bja/aeg178

4. Wang, CJ, Kavanagh, PL, Little, AA. Quality-of-care indicators for
children with sickle cell disease. Pediatrics 2011; 128: 484--493. doi:
10.1542/peds.2010-1791

5. Shah SS, Ranaivo HR, Mets-Halgrimson RB, Rychlik K, Kurup SP.
Establishing a normative database for quantitative pupillometry in the
pediatric population. \emph{BMC Ophthalmol} . 2020;20(1):121.
doi:10.1186/s12886-020-01389-x

6. Aslan MG, Uzun F, F\selectlanguage{polish}ı\selectlanguage{english}nd\selectlanguage{polish}ı\selectlanguage{english}k H, Ka\selectlanguage{ngerman}çar M, Okutucu M, Hocao\selectlanguage{polish}ğ\selectlanguage{english}lu \selectlanguage{ngerman}Ç.
Pupillometry measurement and its relationship to retinal structural
changes in children with attention deficit hyperactivity
disorder.\emph{Graefes Arch Clin Exp Ophthalmol} . March 2020.
doi:10.1007/s00417-020-04658-z

7. Bertrand AL, Garcia JBS, Viera EB, Santos AM, Bertrand RH.
Pupillometry: The Influence of Gender and Anxiety on the Pain
Response.\emph{Pain Physician} .:10.

8. Jain M, Devan S, Jaisankar D, Swaminathan G, Pardhan S, Raman R.
Pupillary Abnormalities with Varying Severity of Diabetic
Retinopathy.\emph{Sci Rep} . 2018;8(1):5636.
doi:10.1038/s41598-018-24015-9

9. Uwaezuoke SN, Ayuk AC, Ndu IK, Eneh C, Mbanefo NR, Ezenwosu OU.
Vaso-occlusive crisis in sickle cell disease: current paradigm on pain
management. \emph{JPR} . 2018;Volume 11:3141-3150.
doi:10.2147/JPR.S185582

10. Connelly MA, Brown JT, Kearns GL, Anderson RA, St Peter SD, Neville
KA. Pupillometry: a non-invasive technique for pain assessment in
paediatric patients. \emph{Archives of Disease in Childhood} .
2014;99(12):1125-1131. doi:10.1136/archdischild-2014-306286

11. Sabourdin N, Diarra C, Wolk R, Piat V, Louvet N, Constant I.
Pupillary Pain Index Changes After a Standardized Bolus of Alfentanil
Under Sevoflurane Anesthesia: First Evaluation of a New Pupillometric
Index to Assess the Level of Analgesia During General
Anesthesia.\emph{Anesthesia \& Analgesia} . 2019;128(3):467-474.
doi:10.1213/ANE.0000000000003681

12. Rollins MD, Feiner JR, Lee JM, Shah S, Larson M. Pupillary Effects
of High-dose Opioid Quantified with Infrared
Pupillometry:\emph{Anesthesiology} . 2014;121(5):1037-1044.
doi:10.1097/ALN.0000000000000384

Table 1 Means and Standard Deviations (SD) for Pupillometry Data

Overall (n=82) Males (n=44) Females (n=38) p-value

Minimum pupil size (mm) 3.52 (0.61) 3.57 (0.66) 3.47 (0.54) 0.495

Maximum pupil size (mm) 5.08 (0.78) 5.11 (0.85) 5.04 (0.71) 0.661

Maximum pupil constriction velocity (mm/s) -4.48 (1.05) -4.40 (0.90)
-4.57 (1.21) 0.482

Average pupil constriction velocity (mm/s) -3.31 (0.73) -3.34 (0.76)
-3.26 (0.69) 0.618

Dilation velocity (mm/s) 1.03 (0.31) 1.07 (0.33) 0.99 (0.27) 0.203

Table 2 Mean Minimum and Maximum Pupil Sizes

Minimum Maximum

Age (years) \# participants pupil size pupil size

{[}mm{]} (SD) {[}mm{]} (SD)

2 -- 3 4 3.03 (0.26) 4.83 (0.29)

4 -- 6 19 3.25 (0.41) 4.83 (0.64)

7 -- 9 15 3.89 (0.55) 5.49 (0.64)

10 -- 12 22 3.49 (0.67) 4.95 (0.86)

13 -- 15 12 3.84 (0.65) 5.51 (0.90)

16 -- 17 10 3.40 (0.50) 4.80 (0.73)

SD = standard deviation

Figure 1 Neuroptics Pupillometer

Figure 2 Scatter plot and regression line of pupil size and dilation
velocity\selectlanguage{english}
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