Yap Tiong Peng

PhD Candidate

PhD Candidate

Research Title: Electrophysiology and psychophysics of children with newly-diagnosed refractive (non-strabismic) amblyopia and the effect of optical treatment

Supervisors: Dr Mei-Ying Boon (UNSW Sydney), Dr Catherine Suttle (City, University of London), A/Prof Chi Luu (University of Melbourne)

Electrophysiology and psychophsyics of children with newly-diagnosed refractive (non-strabismic) amblyopia and the effect of optical treatment

Optical treatment is the primary treatment of all types of amblyopia that has a refractive component. However, it is unclear how optical treatment impacts cortical processing in amblyopic children as some of them may readily improve letter recognition visual acuity (treatment responders) but others may not (treatment non-responders). The main aim was to investigate the electrophysiological and psychophysical effects of optical treatment in children who have been newly-diagnosed with amblyopia in comparison with normal maturation in non-amblyopic children.  The secondary aim was to explore whether pattern onset-offset visual evoked potentials (POVEPs) and psychophysical grating acuities (GA) may be predictive of clinically significant improvements in letter recognition visual acuity (VA) after four months of optical treatment.

The primary outcome measures were POVEP C3 amplitude and C3 latency and GA which were assessed in response to orientation-specific stimuli. The testing protocol was designed to optimize the assessment of meridional anisotropies and was able to identify children with refractive amblyopia and to monitor treatment outcomes.

The study presented evidence that four months of optical treatment improved POVEP C3 amplitude on average, although within the amblyopic group, a subset of refractive amblyopes were not found to significantly improve in letter visual acuity. A comparison control group, comprised of non-amblyopic children, were also monitored over two visits four months apart, which represented age-normal characteristics and maturation.

Meridional anisotropies were found to be a potentially useful indicator of normality, as there was evidence that orientation-specific neural mechanisms differed for the responders and non-responders to optical treatment, with the responders showing anisotropies more consistent with the control data. An onset of horizontal effect may indicate that the amblyopic visual systems are improving. Consequently, lower POVEP C3 amplitude in response to horizontally oriented grating stimuli at baseline was found to be a potential predictor of responder status after four months of optical treatment.

The findings added new knowledge into the understanding of the electrophysiological and psychophysical effects of optical treatment in refractive amblyopia. The PhD thesis by Dr Yap Tiong Peng was examined and graded excellent and outstanding by the examiners. He also received a nomination for the Dean's list of outstanding PhD theses.  


Yap Tiong Peng is an Optometrist in private practice in Singapore. He graduated from UMIST (Manchester) and Imperial College (London). Together with a team of six other optometrists in his practice, he spends most of this time working on neurodevelopmental vision therapy and seeing children with learning challenges and special-needs. In 2012, he started his PhD journey with the objective of studying the neurodevelopment of children with refractive amblyopia. His research data collection takes place mainly at the Visual Electrophysiology Laboratory at the Singapore National Eye Centre (SNEC), but also occasionally at UNSW in Sydney.



University of Manchester (BSc Hons, Optometry, 2:1, 2001)

University of London – Imperial College (MSc, Bioeng, 2003)

Imperial College of Science, Technology and Medicine (DIC, 2004)



Journal Articles

Yap TP, Luu CD, Suttle CM, Chia A, Boon MY. Electrophysiological and Psychophysical Studies of Meridional Anisotropies in Children With and Without Astigmatism. Invest Ophthalmol Vis Sci. 2019; 60(6):1906-1913. doi: 10.1167/iovs.18-25924. https://iovs.arvojournals.org/article.aspx?articleid=2732643

Yap TP, Luu CD, Suttle C, Chia A, Boon MY. Is there meridional anisotropy in children with normal visual acuity and different astigmatic refractive errors? An electrophysiological and psychophysical study (ARVO Abstract). Invest Ophthalmol Vis Sci, 2018; 59(9):4118. https://iovs.arvojournals.org/article.aspx?articleid=2691805

Boon MY, Leung H, Suttle C, Luu CD, Yap TP, Hing S. Suprathreshold VEPs as an indicator of abnormal cortical processing in nonstrabismic amblyopes (ARVO Abstract). Invest Ophthalmol Vis Sci, 2018, 59: 4120. https://iovs.arvojournals.org/article.aspx?articleid=2693807

Yap TP, Luu CD, Suttle C, Chia A, Boon MY. The effect of grating stimulus orientation on monocular pattern onset-offset VEPs and psychophysical grating acuity in young children with newly-diagnosed refractive amblyopia (ARVO Abstract). Doc Ophthalmol, 2018; 136:3-52.

Yap TP, Luu CD, Suttle C, Chia A, Boon MY. Transient VEPs in children with bilateral refractive amblyopia (ISCEV Abstract). Doc Ophthalmol, 2016; 133: 9 -41.

Boon MY, Suttle C, Leung H, Hing S, Yap TP, Luu CD. Binocular summation of luminance and chromatic contrast stimuli in children with unilateral or bilateral amblyopia (Abstract of ARVO). Invest Ophthalmol Vis Sci, 2013, 54: 3997. https://iovs.arvojournals.org/article.aspx?articleid=2148824

Wagle AM, Lim WY, Yap TP, Neelam K, Au Eong KG. Utility values associated with vitreous floaters. Am J Ophthalmol. 2011;152(1):60-65.e1. doi: 10.1016/j.ajo.2011.01.026. Epub 2011 May 12. https://www.ajo.com/article/S0002-9394(11)00064-X/fulltext

Yap TP, Wagle AM, Tai BC, Au-Eong KG, Yip CC. Three-drops 1% tropicamide regime and its effect on pupil size and rate of mydriasis: a comparison among different races and diabetes (Abstract of the 17th Asia Pacific Optometric Congress). Clin Exp Optom, 2010; 93:3:189-203. https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1444-0938.2010.00464.x


Reports and Book Chapters

Yap TP. Dyslexia and vision: a review of current evidence and clinical interventions. Medical Grapevine Asia, 2013; 09: 10-15.



ARVO Publications Grant (2019)



ARVO Annual Meeting (USA)

AAO Annual Meeting (USA)

BrSCEV Annual Meeting (UK)

COVD Annual Meeting (USA)

ICBO Annual Meeting (UK & Australia)

ISCEV Annual Meeting (Singapore, France & Korea)

NACBO (Melbourne and Sydney)



American Academy of Optometry (AAO, USA)

Australasian College of Behavioural Optometrists (ACBO, Australia)

Association for Research in Vision and Ophthalmology (ARVO, USA)

British Society for Clinical Electrophysiology of Vision (BriSCEV, UK)

British Association of Behavioural Optometrists (BABO, UK)

College of Optometrists in Vision Development (COVD, USA)

Imperial College Alumni Association of Singapore (Executive Committee Member and Former VP)

International Society for Low Vision Research and Rehabilitation (ISLRR)

International Neuro-optometric Rehabilitation Association (NORA)

Occupational and Environmental Health Society (OEHS, Singapore)

Singapore Optometric Association (SOA, Singapore)

University of Manchester Alumni Association of Singapore (Former Vice President)