Four-Dimensional Ultrasound Analysis of Fetal Independent Oculomotor Control

Four-Dimensional Ultrasound Analysis of Fetal Independent Oculomotor Control

Amy Jane Cunliffe-Penman

2017

This dissertation seeks to enhance the present understanding of elicited fetal independent ocular-motor control during late gestation. Independent ocular-motor control refers to the ability to more the eyes independently from the head when fixating on a visual stimulus. Whilst there is a wealth of information regarding fetal visual development and responsiveness to light stimulation, there is a paucity of research investigating elicited fetal visuo-motor abilities. Therefore, the current research aims to utilsise four-dimensional ultrasound imaging to view fetal responsiveness when exposed to a custom-made light source. To assess fetal independent ocular movement, light was presented through the maternal abdomen (N=54) towards the peripheral of the fetal head to elicit directed purposeful eye and head movements. Ultrasound scans were recorded and later coded for frequency of eye and head movements at each stage of light exposure (before, during and after light). The primary experimental hypothesis suggested that the fetus would exhibit independent ocular-motor control when exposed to a light stimulus and that, the fetus would produce behavioural responses more often during light stimulation, than in the absence of light stimulation. Analysis of results indicated that the fetus was able to make independent, directed ocular movements towards stimuli during late gestation. Eye movements were more frequent during and after light exposure, in comparison to before light exposure. Head movements were more common during light exposure; however, head movements were more commonly performed by the fetuses than eye movements overall. The results suggest that the fetal visual system maybe more advanced than previously thought and may provide clinical implications, as independent ocular movement may be utilised as a neurological diagnostic tool

Four-dimensional Ultrasound Imaging
Fetal Visual Development
Third Trimester
Light Stimuli
Independent Oculomotor Control

Experimental Design
The study employed a repeated-measures, within-subjects design, in which one sample of participants were exposed to a light stimulus and assessed for behavioural responses before, during and after light exposure. The independent variable manipulated light stimuli presentation time (before stimulation, during stimulation and after stimulation). The dependent variable measured the frequency of behavioural responses (head movements and eye movements) elicited at each stage of light exposure. The participants were counterbalanced in regards to the presentation of two forms of light exposure (constant beam and intermittent beam, described below) to avoid the introduction of confounding variables and reduce the possibility of order effects.
Three extraneous variables were identified however; this included maternal abdominal thickness, fetal positioning and external room illumination. Maternal abdominal thickness was controlled for by first assessing maternal thickness before the experimental procedure and then altering the light strength dependant on this factor. Therefore, if the thickness was greater, a stronger light strength would be used to ensure light reached the fetal retina in accordance to Del Giudice’s (2011) model of light penetration. There were three different light strengths employed within this study, as will be discussed below.
Furthermore, fetal positioning was considered an extraneous variable as the location of light exposure on the maternal abdomen was dependant on the fetus’s position within the womb. To ensure light was presented to the same location for each participant, an initial examination was conducted to determine the orientation of the fetus. Then, the light source was positioned towards the peripheral of the fetus head. Conducting this initial examination increased research validity as each fetus experienced the light similarly and was able to perform horizontal eye and head movements.
Lastly, external room illumination was an important factor to consider, as if the room was not dark, it was possible the light stimulus would not have had an experimental effect. Room illumination was controlled for by conducting the experimental procedure only in complete darkness to ensure no other light could reach the fetus and influence fetal responsiveness.
Materials
Light Stimulus. The light stimuli employed within the current study was a customised, ethically approved light source which emitted light at 650nm. The light stimulus was specially constructed to ensure extraneous variables, such as light strength and maternal thickness, could be controlled for. The stimulus was assembled using a custom-made semiconductor laser torch. The torch was created with a triangular shape at the end, which included three dots, each distanced 15mm apart. Three dots were used to provide a smaller light guide, as this has been described to provide better fetal response rate (Dunn et al, 2015). Utilising Del Giudice’s (2010) model of light penetration, the light source was adjustable to ensure 0.1-1% of light reached the fetus and was within the range of the fetal visual system. In addition, red spectrum lumen levels were used, as this wavelength penetrates tissue most successfully when compared to other colour spectrums (Dunn et al., 2015). An advantage of employing red spectrum wavelengths means lower levels of light can be presented, without reducing the amount of light reaching the fetal retina.
An important component of the light stimulus was the ability to alter light strength depending on maternal abdominal thickness. More specifically, the light was calibrated at output optical powers of 0.5mW, 1mW or 5mW for thickness (t) below 1.5cm, between 1.5cm and 3cm and above 3cm. To control for variations in light stimulation in regards to maternal thickness, and to ensure a constant level of light was experienced by every fetus, dependent optical powers were delivered.
Ultrasound Machinery. Observations of eye and head movements were recorded during experimental ultrasound scans, located at either Cumbria University Medical Imaging Unit or Blackpool Victoria Hospital. At Cumbria University Medical Imaging Unit, a GE Healthcare Voluson iBT07 4D live ultrasound scanner and 4D probe, model RAB4-8-RS was used. Also, at Blackpool Victoria Hospital using a GE Healthcare Voluson E8 Expert BT13 advanced 4D HD live ultrasound scanner and 4D probe, model RM66. The ultrasound recordings were streamed onto a laptop during the scans and then saved on to an external hard drive, which contained no previous data. The external hard drive was used for coding of eye and head movements offline, at a private location on Lancaster University campus.
Procedure
On arrival at one of the two medical clinics, either located at Blackpool Victoria Hospital or Cumbria University Medical Imaging Unit, the participant was greeted by a researcher and taken into a room containing an ultrasound imaging machine. The participant was introduced to the sonographer and then asked to remove all items of clothing covering the abdomen and to lie down on a medical bed. When the participant voiced their comfort, the sonographer proceeded in applying a lubricating jelly to the area of examination on the abdomen. The lubricating jelly was used to ensure smooth movement of the probe against the skin during the ultrasound scan. The sonographer then placed the probe onto the abdomen and began the first 2D ultrasound scan to assess the maternal tissue thickness (in millimetres) and to determine the fetal head position.
These assessments were undertaken to inform the experimenter of where the light stimulus should be presented and the strength of the light needed, in order to reach the fetal retina. Tissue thickness was measured from maternal skin to uterine wall and ranged between 1cm and 5cm thick. Del Guidice’s (2010) model of light penetration was employed to determine the strength of light needed. During the ultrasound assessment and experimental procedure, the 3D and 4D scans were broadcasted simultaneously to both the ultrasound machine and a laptop which recorded the scans onto an external hard drive. Once it was concluded, there were no fetal abnormalities and the light strength and fetal orientation had been established, the participant was asked to remain motionless to preserve image acuity and light source position. The lights in the room were then switched off, and the experimental study began. The custom-made light source was presented to the participant’s abdomen, showing a three dotted red light in two stages of light exposure. The times in which the light source was turned on and off, as well as the minutes measured, were noted and recorded by the experimenter on a data collection sheet and were controlled using a digital stop watch. The two stages of light exposure were randomised between participants to counterbalance the sample and reduce order effects. When the experimenter was ready to switch on the light source and begin testing, they would signal the sonographer so that both the 4D scan recording, the light source, and stopwatch were all started at the same time. In the first stage of light exposure, light was presented to the fetus in a constant stationary beam for 3 minutes, presented to the periphery to the side of the fetus. There was then a break period between the two stages of light exposure, to allow the participant, sonographer, and researchers to readjust their positions. The second stage of light exposure consisted of 10 intermittent beams of light, in which timing between each light beam was again controlled by an experimenter using a digital stopwatch. This stage of light was created according to the procedure of Johnson and Morton (1991), in which a light stimulus was slowly presented to the fetus along the arc of a protractor. The light was presented at a rate of around five degrees per second when the fetal head was positioned on the protractor mid-line at zero degrees. Therefore, the present study decided the second form of light would be presented to the side of the fetal head and then moved away from the head position horizontally across the abdomen for approximately five seconds, at a rate of 1 centimetre per second. After the assigned five seconds, the light source was temporarily switched off and the 4D scan turned to a 2D scan for around 20 seconds, following which the 5 second light exposure would then begin again. As aforementioned, this stage was repeated 10 times over a 3 minute period. On completion of both stages of light exposure, the experiment was finished, and the participants were thanked for their cooperation. Each scan recording ranged from between 8 to 22 minutes, corresponding to safety standards (Harr, 2011). All recordings were saved onto a specific file on an external drive and stored in a filing cabinet in the Lancaster University Psychology Department. The hard drive was kept separate from the light presentation times and mothers personal details, which were stored elsewhere in the department to retain maximum confidentiality and security.
Data Coding
Data was gathered from the participants by recording and coding 4D ultrasound real-time videos for fetal movements in response to a light stimulus. Consequently, a specific coding process needed to be established to certify all researchers were coding matching responses and ensuring research validity. The ultrasound recordings were coded using an external hard-drive and Mac computer. During a research team meeting, the experimenters agreed on four specific behavioural responses that would be coded for, before stimuli, during stimuli, and after stimuli. Coding for before stimuli was conducted for only the first three minutes before the first light exposure stage began, meaning if light stimulation began at eight minutes on the ultrasound recording, only five minutes onward would be coded for potential ‘before stimuli’ movement. The short break between the two light exposure stages was coded as after stimuli, despite additional stimulation being presented after a short interval. A timed approach was decided as the fetus had previously been exposed to light, therefore, possible continued fetal activation could influence behavioural response. Initially, the researchers observed several scans to better understand the procedure and to examine the characteristics of the data, in which four behaviours were clearly demonstrated. These four behaviours were used as the categories for coding movement. The first response was named ‘head movement, with eye movement’; the second response was ‘head movement, eyes move first’; the third response was ‘head movement, cannot depict eye movement' and the fourth response was ‘independent eye movement’. An excel spreadsheet was used to code the frequency of behavioural responses in three columns, before, during and after stimuli. Within these columns were a further four columns with each of the four possible behavioural responses. When a movement was observed, the participant number and time was noted in a row and a number one was placed in the corresponding behavioural column located on the same row.
To reduce subjectivity during coding it was agreed that eye movements were to be coded when the probe was stationary and the light stimulus (displayed as a white dot on the 2D image scan) moved in any direction over the abdomen. Head movements were coded only when the centre position of the head moved clearly either right or left and up or down. This is important as the fetus often made small movements or moved their limbs, which may cover and/or reposition the head. Such movements could be confused with a singular head movement; therefore, only centre position movements were included in the coding data sheet. In addition, other non-fetal movements the researchers needed to be aware of included movement of the probe, as the probe was occasionally moved to gain greater image acuity. To identify this, the researchers agreed that the surrounding environment in utero must remain motionless as the head moves, such as the line representing the edge of the maternal uterus wall. Similarly, this rule was implemented when the mother breathed, as the fetus can appear to move, potentially causing further coding confusion. Thus, fetal head movements were only included in the data set if the external image was unmoving.
Data Reduction
Data clearing was conducted in an effort to increase internal research validity. Participant data was not submitted for behavioural coding if the fetal position could not be established or clearly seen during the ultrasound procedure. Visual acuity was particularly important during the experiment to determine where the light stimulus would be presented, therefore, if the fetal position was not clear, the light could not be accurately exposed to the peripheral of the fetus. Additionally, 12 individuals were later excluded from data analysis, as when coding for behavioural responses, the fetus was inactive and showed no movements. Inactivity meant a lack of any fetal actions available during behavioural coding, considered a sleep state in the fetal behavioural literature, therefore, the data was not included in the overall analysis.

Lancaster University

data/SPSS.sav

CunliffePenman2017

John Towse

Open

None

English

LA1 4YF

Vincent Reid

MSc

Developmental Psychology

Fifty-four participants were recruited, consisting of healthy pregnant women with singleton healthy fetuses

Wilcoxon Signed-Ranks test