An observational study in Binocular Visual Function, sponsored by Tan Tock Seng Hospital. Recruiting at 1 site in Singapore. Open to participants aged 21 Years to 59 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-01-09.
Sponsored by Tan Tock Seng Hospital · Observational
The assessment and monitoring of the field of binocular single vision remains a crucial aspect of ophthalmological care, yet current clinical practice relies on normative standards established by Feibel \& Roper-Hall in 1974 that present significant limitations for contemporary application. The original study, conducted with a demographically homogeneous Caucasian population in St Louis using only "several" normal individuals, raises concerns regarding its applicability to Asian populations, particularly in Singapore, where ethnic and genetic factors may influence ocular characteristics. The limited sample size significantly increases the likelihood of Type II errors, whilst the temporal gap of over five decades introduces additional concerns regarding population changes, environmental factors, and advances in measurement techniques that have not been incorporated into current normative data. Given these substantial limitations in demographic representation, statistical power, and temporal relevance, there exists a pressing need to establish population-specific normative data for the field of binocular single vision in Singapore's adult population, which would provide more clinically relevant reference values and potentially improve diagnostic accuracy for ocular conditions in the local context.
The assessment and monitoring of the field of binocular single vision is a crucial aspect of ophthalmological care, particularly in the management of oculoplastics and strabismus. Currently, clinicians worldwide, including those in Singapore, rely on the normal boundary of the field of binocular single vision established by Doctor Robert M. Feibel \& Gill Roper-Hall in 1974 as the gold-standard parameter for clinical assessment. However, this long-standing standard raises several significant concerns regarding its applicability to our current population.
The original study by Feibel \& Roper-Hall was conducted in St Louis, Missouri, United States of America, with participants who were likely of Caucasian descent. This demographic composition presents a potential limitation when applying these standards to Asian populations, particularly in Singapore, where ethnic and genetic factors may influence ocular characteristics. Furthermore, the study's methodology involved only "several" normal individuals, suggesting a sample size of more than two but fewer than ten participants. A sample size of this limited scope significantly increases the likelihood of Type II errors, potentially compromising the statistical power and reliability of the established normative values.
The temporal gap of over five decades since the original study adds another layer of concern. Population characteristics, environmental factors, and lifestyle patterns have undergone substantial changes during this period, potentially affecting ocular health parameters. Additionally, advances in measurement techniques and an understanding of ocular physiology suggest the need for updated normative data that reflect current population characteristics and incorporate modern assessment methodologies.
Given these limitations, there is a pressing need to establish population-specific normative data for the field of binocular single vision in Singapore's adult population. This would not only provide more relevant reference values for clinical assessment but also potentially improve the accuracy of diagnosis and monitoring of various ocular conditions in our local context.
Tan Tock Seng Hospital is the lead sponsor of 103 studies on the registry; 17 are open to participants now.
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Healthy Individuals
Language comprehension: Able to understand verbal spoken instructions in:
Exclusion Criteria:
- Communication barrier: Unable to understand verbal spoken instructions
Medical history:
Near visual acuity:
o Right eye \& Left eye monocularly, binocularly unaided near vision: worse than N6 at 40cm from participant's nose
Ocular alignment:
o Prism cover test at near (30cm) of equal or greater than 10 prism diopters at these positions of gaze:
Extraocular movement:
o Extraocular movement of over-action or under-action of equal or greater than 0.5 in any of the nine cardinal positions of gaze
Confrontational Visual field:
o Abnormal monocular visual field on confrontational visual field test
The intervention involves a single field of binocular single vision assessment using the Takagi MT-325UD Projection Perimeter. Participants undergo binocular testing where they fixate and follow a single round light stimulus as it moves throughout the perimeter bowl. When participants perceive two distinct light stimuli (indicating loss of binocular single vision), they press a buzzer. The orthoptist records these responses and plots the boundaries on a standardised recording sheet to map the participant's field of binocular single vision. This intervention addresses significant limitations of the current gold standard established by Feibel \& Roper-Hall (1974). The original study was conducted with "several" normal individuals (likely fewer than 10 participants) of Caucasian descent in St Louis, Missouri, creating potential issues with statistical power and population applicability. Our study uses a larger, more robust sample size of 32 participants specifically from Singapore's Asian
Field of Binocular Single Vision in Asian population
Establish comprehensive normative range of field of binocular single vision (BSV) specifically for healthy adults in Singapore's population aged 21-59, creating locally relevant reference standards that reflect ethnic, genetic, and contemporary population. BSV is the ability to use both eyes simultaneously and coordinate the slightly different images from each eye into a single, unified, three-dimensional mental percept. The "field of binocular single vision" is the specific area within the overall visual field where this fusion and single vision can be maintained. To measure the field of BSV using Goldmann perimetry, a moving light stimulus is presented while the patient uses both eyes. The test maps the area where the patient can maintain fusion (single vision). The boundary where fusion breaks (and diplopia starts) is plotted across different directions to define the BSV field.
Time frame: up to 20 minutes during 1 study visit.
Comparison of current field of binocular single vision gold standard between Caucasian population vs Asian population
Conduct rigorous statistical comparison between newly established Singapore normative values and existing Feibel \& Roper-Hall (1974) standards to quantify differences and determine clinical significance. Current benchmarks are based on a 1974 U.S. study by Feibel \& Roper-Hall that involved fewer than ten Caucasian subjects and no Asian representation. Consequently, clinicians may over- or under-diagnose ocular deviation and fusion deficits in Asian patients. The study validates a modern methodology using the Takagi MT-325UD Projection Perimeter to map BSV fields under standardized conditions.
Time frame: Up to 20 minutes during 1 study visit.
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