Stephanie Obeng-Inkoom, Paediatric Optometry Fellow

Paediatric Optometrist, Korle bu Teaching Hospital, Ghana

A. Introduction

Infants have certain visual functions present at birth. However, they do not have good peripheral vision. Their visual field extends to the adult value of around 80° at 10 months of age.⁽¹⁾ Some neurological and ocular diseases cause visual field deficits such as hemianopia and field constriction in young children. Early treatment following the detection of visual field deficits helps prevent loss of central vision in the future.⁽²⁾ In clinical practice, confrontation test is the most used technique to assess the visual fields of Paediatric patients, but this technique is non quantitative and most often unreliable and inconsistent. ⁽³⁾ The standard conventional perimeter requires cooperation and understanding. Children have less cognitive maturity and short attention span than adults hence assessing this visual function becomes a challenge. ^{(4, 5)} This blog is a summary of efforts made towards the development of quantitative visual field-testing tools in children.

B. Efforts to develop visual field analysis tools

Preferential looking Perimeter

Allen et. al., developed a tool “KidzEyez” which showed promising results when compared with confrontation test results in their study. It uses preferential looking responses to assess the integrity of the visual field in young and developmentally delayed children (3-10 years). Patient sits in front of a plasma screen with a webcam mounted below. Central fixation is elicited with a cartoon video playing in the centre and square targets presented as the peripheral stimulus. The clinician watches the eye movements from the webcam and scores as “seen” or “unseen” depending on the patient’s gaze direction.⁽²⁾

Figure 1. Shows a captured image of the clinician’s monitor showing the webcam image of the patient fixating at the cartoon video. Picture the pink superimposed square shows to the clinician the position of the next peripheral target and picture B, the target becomes green when presented.

Image courtesy: Allen, L. E., Slater, M. E., Proffitt, R. V., Quarton, E., &Pelah, A. (2012). A new perimeter using the preferential looking response to assess peripheral visual fields in young and developmentally delayed children. Journal of American Association for Pediatric Ophthalmology and Strabismus, 16(3), 261-265.

Light-Emitting Diode (LED) Perimeter

This perimeter uses LED lights within a hemispheric dome to map visual fields in infants (2-12 months) and patients with special needs. The dome is covered with a black cloth and the patient placed in a supine position on a mattress. Central target (LED) is used to maintain fixation and then turned off when the peripheral LED stimulus is presented. Gross visual field (GVF), Visual field extent (VFE) and time taken for the infant to look at the stimulus, that is, the Reaction time (RT) is measured. Satgunam et al obtained quantifiable variables for RT with GVF and a complete visual field isopter was plotted in one sitting even though visual field losses beyond 50 degree were not captured due to the nature of the dome.⁽⁶⁾

Figure 2: Schematic diagram of the Pediatric Perimeter device showing the skeletal structure of the hemispherical dome and a magnified screen snapshot of an infant getting tested.

(Picture courtesy: Satgunam, P., Datta, S., Chillakala, K., Bobbili, K. R., & Joshi, D. (2017). Pediatric Perimeter—A Novel Device to Measure Visual Fields in Infants and Patients with Special Needs. Translational Vision Science & Technology, 6(4), 3-3).

Video game- based perimeter

Children aged between 4 to 14 years were made to sit at an apparatus designed in a castle structure. The child is taught to “squash the tomato” (to maintain central fixation) and to kill the ghost when it is seen (peripheral target). Aslam et. al., reported that although two of the children had abnormal fields due to the complexity of the game, they still successfully completed it. ⁽⁷⁾

Figure 3: Shows the image of the tomato being squashed

Figure 4: Shows the peripheral ghost being lasered. (Picture courtesy: Aslam, T. M., Rahman, W., Henson, D., &Khaw, P. T. (2011). A novel pediatric game-based visual-fields assessor. British Journal of Ophthalmology, 95(7), 921-924).

Remote Eye Tracking

Pel et. al., in their study made children aged between 2-9 years sit at 60cm from a monitor combined with an eye tracking system which measures the gaze position of the eyes using the reflection from the cornea. Targets consisting of large and high contrast cartoons were showed in the corner of the monitor and the Saccadic Reaction Time (SRT) and time the gaze was within 6 degrees from the target centre, that is, Reaction Time to Target Fixation(RTF) were recorded. They concluded that, the eye tracking provides quantifiable timing variables as well as perform oculomotor fixations during orienting behaviour tasks and can be used in children with brain damage or developmental disorders.⁽⁸⁾

Figure 5: Shows an image of the cartoons being displayed in the corner of the monitor. The gaze position of the patient is initially seen at the lower left corner and ends with a steady fixation in the upper right corner. The white dashed circle shows the target area.

(Picture courtesy: Pel, J. J. M., Manders, J. C. W., & Van der Steen, J. (2010). Assessment of visual orienting behaviour in young children using remote eye tracking: methodology and reliability. Journal of Neuroscience Methods, 189(2), 252-256).

Conclusion

Standard visual field tests are not well tolerated by pediatric patients. Novel techniques are being developed to expand the potential to evaluate their visual fields quantitatively and reproducibly. Further studies are needed to validate these methods and made available for commercial use.

References

1. Daw, N. W., &Daw, N. W. (2006). Visual development(Vol. 9). New York: Springer.
2. Allen, L. E., Slater, M. E., Proffitt, R. V., Quarton, E., &Pelah, A. (2012). A new perimeter using the preferential looking response to assess peripheral visual fields in young and developmentally delayed children. Journal of American Association for Pediatric Ophthalmology and Strabismus, 16(3), 261-265.
3. Pandit, R. J., Gales, K., & Griffiths, P. G. (2001). Effectiveness of testing visual fields by confrontation. The Lancet, 358(9290), 1339-1340.
4. Safran, A. B., Laffi, G. L., Bullinger, A., Viviani, P., de Weisse, C., Desangles, D&Mermoud, C. (1996). Feasibility of automated visual field examination in children between 5 and 8 years of age. British journal of ophthalmology, 80(6), 515-518.
5. Tschopp, C., Safran, A. B., Viviani, P., Bullinger, A., Reicherts, M., &Mermoud, C. (1998). Automated visual field examination in children aged 5–8 years: Part I: experimental validation of a testing procedure. Vision research, 38(14), 2203-2210.
6. Satgunam, P., Datta, S., Chillakala, K., Bobbili, K. R., & Joshi, D. (2017). Pediatric Perimeter—A Novel Device to Measure Visual Fields in Infants and Patients with Special Needs. Translational vision science & technology, 6(4), 3-3.
7. Aslam, T. M., Rahman, W., Henson, D., &Khaw, P. T. (2011). A novel pediatric game-based visual-fields assessor. British journal of ophthalmology, 95(7), 921-924.
8. Pel, J. J. M., Manders, J. C. W., & Van der Steen, J. (2010). Assessment of visual orienting behaviour in young children using remote eye tracking: methodology and reliability. Journal of Neuroscience Methods, 189(2), 252-256.