Pilot Study of Normative Range of Field of Binocular Single Vision in Adults in Singapore (NORVIBAS)

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.

Study Overview

• Status: Recruiting
• Conditions: Binocular Visual Function
• Intervention / Treatment: Diagnostic test: Field of Binocular Single Vision

Detailed Description

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.

• Study Type: Observational
• Enrollment (Estimated): 30

Contacts and Locations

• Study Contact: Name: Zheng Kuang Noel Soh, BSc; Phone Number: +65 6357 3693; Email: zheng.kuang.soh@nhghealth.com.sg

Study Locations

• Singapore
  • Singapore
    • Singapore, Singapore, Singapore, 308433
      • Recruiting
      • Tan Tock Seng Hospital
      • Contact: Zheng Kuang Noel Soh, BSc; Phone Number: +65 6357 3693; Email: zheng.kuang.soh@nhghealth.com.sg
      • Principal Investigator: Daniel Chin, MBBS
      • Sub-Investigator: Yan Tong Koh, MBBS
      • Sub-Investigator: Sebastian Yue, MSc
      • Sub-Investigator: Jackson Chng, BSc
      • Sub-Investigator: Azizah Binte Hajamohideen, BSc
      • Sub-Investigator: Zheng Kuang Noel Soh, BSc

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

Healthy Individuals

Description

Inclusion Criteria:

• Age: 21 to 59 years old
• Gender: Males or females
• Ethnicity: Asian descent.

• Language comprehension: Able to understand verbal spoken instructions in:

  • British/American English

  • Mandarin Chinese
  • Bahasa Melayu
• Protocol compliance: Ability to comply with the study protocol, as determined by the investigator's judgment
• Consent capacity: Must be able to understand and provide informed consent, with signed informed consent form required before any study assessments

Exclusion Criteria:

- Communication barrier: Unable to understand verbal spoken instructions

• Medical history:

  • Any facial trauma
  • Any ocular trauma
  • Any head trauma
  • Any history of ocular disease
  • Any history of ocular surgery
  • Systemic condition(s)

• 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:

  • Primary gaze
  • Right gaze
  • Left gaze
  • Up gaze
  • Down 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

• Hess chart test o Abnormal or asymmetry in pattern of extraocular muscle action in Hess chart test

Study Plan

How is the study designed?

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	up to 20 minutes during 1 study visit.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	Up to 20 minutes during 1 study visit.

Collaborators and Investigators

• Sponsor: Tan Tock Seng Hospital
• Investigators: Principal Investigator: Daniel Chin, MBBS, Tan Tock Seng Hospital; Study Director: Sebastian Yue, MSc, Tan Tock Seng Hospital

Publications and helpful links

General Publications

• Feibel RM, Roper-Hall G. Evaluation of the field of binocular single vision in incomitant strabismus. Am J Ophthalmol. 1974 Nov;78(5):800-5. doi: 10.1016/0002-9394(74)90303-1. No abstract available.
• Kakizaki H, Umezawa N, Takahashi Y, Selva D. Binocular single vision field. Ophthalmology. 2009 Feb;116(2):364. doi: 10.1016/j.ophtha.2008.08.046. No abstract available.

Study record dates

Study Major Dates

• Study Start (Actual): October 15, 2025
• Primary Completion (Estimated): June 30, 2026
• Study Completion (Estimated): October 14, 2026

Study Registration Dates

• First Submitted: November 20, 2025
• First Submitted That Met QC Criteria: November 20, 2025
• First Posted (Estimated): December 2, 2025

Study Record Updates

• Last Update Posted (Actual): January 9, 2026
• Last Update Submitted That Met QC Criteria: January 7, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: Binocular field of vision
• Other Study ID Numbers: 2025-1293

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Participant data cannot be shared due to local governing laws and institutional regulations.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No