New Visual Acuity and Crowding Tests for Better Detection of Amblyopia

July 20, 2021 updated by: Anglia Ruskin University

Examination of New Visual Acuity and Clinical Crowding Tests for Better Detection of Amblyopia

Amblyopia, or 'lazy eye', is the reduction in vision usually in one eye, due to abnormal visual development without organic cause. It is a preventable and leading cause of monocular vision loss (prevalence of around 3%) and increases lifetime risk of bilateral visual impairment from 10% in the general population, to 18% in amblyopes.

In the UK, vision screening in children aims to detect amblyopia and other undiagnosed visual conditions. Laboratory research suggest that amblyopia could be better detected by modifying standard clinical vision tests to enhance and quantify "crowding". Crowding is the negative effect that surrounding features have on the visibility of a target. Crowding distance and crowding magnitude are considerably greater in amblyopic eyes than in normal healthy eyes. Modifications that should lead to improved amblyopia detection are 1) place letters closer together on a vision chart, 2) define letters by contrast, rather than luminance, and 3) use a new thinner font in the form of numbers, to allow crowding distance in central vision to be measured. In this project, these modifications will be tested in amblyopic children for the first time.

Amblyopic children aged 3 to 11 years (n=32) will be recruited from ACPOS (Addenbrooke's Community Paediatric Ophthalmology Service) at ARU. They will have their vision measured with the three modified tests as well as an uncrowded test. The child will view letters and numbers on a computer screen and respond (verbally or by indicating their choice on a matching card). Testing is fun and game-like with breaks for rewards. Results will be compared to standard vision measurement (SLT: Sonksen LogMAR Test) from the child's ACPOS visit. Amblyopic data will be compared to control data from normal healthy children aged 3 to 11 years (n=200), and age-matched children with normal vision (n=16) from ACPOS (false referrals from school screening).

Study Overview

Status

Active, not recruiting

Conditions

Intervention / Treatment

Detailed Description

In the UK, a national vision screening is employed to detect amblyopia and other undiagnosed visual conditions in school-aged children, so that they can be managed effectively. Better detection of amblyopia could be achieved by modifying current visual acuity tests, which measure the spatial resolution limit (or capacity for clarity and sharpness) of vision and by measuring crowding distance; previously unmeasured in a clinical setting. By strengthening crowding magnitude, and better quantifying its spatial distance in paediatric populations, it is hoped that the ability to detect amblyopia, and monitor its improvement with treatment will be significantly enhanced.

Three recent suggestions regarding modifications to current visual acuity tests may lead to improved detection of crowding-sensitive conditions, such as amblyopia. First, closer placement of surrounding letters to the target letter should increase the magnitude of crowding in the amblyopic eye in particular, leading to increased visual acuity differences between eyes. Second, contrast modulated stimuli should enhance crowding in amblyopic eyes. Third, a new thinner font will allow clinical measures of foveal crowding distance. In this project, these three modifications will be tested for the first time in the target clinical population.

Several studies reported that optotypes (letters or symbols) on a vision chart should be placed closer together than they currently are on commercially-available charts, which use 2.5 to 5 stroke-widths separation between target and neighbouring letters. Closer placement disrupts target optotype identification in normal peripheral vision and in central vision of amblyopic eyes due to crowding. In one vision test in the proposed study, a laterally-reversible target letter (e.g., H, O, T or V) will be surrounded by four other letters (U, A, L, C). This arrangement, in which letters were separated by 0.5 optotype widths (or 2.5 stroke widths) was first formally used in the Cambridge Crowding Test. In the proposed experiments, the surrounding letters will be placed 1 stroke-width away from the target letter, the optimal position recommended by recent studies.

Visual acuities for target letters will be measured for both amblyopic and non-amblyopic eyes of child participants, in a clinical environment. These results will be compared with visual acuities acquired during the clinical appointment using the Sonksen logMAR Test (SLT), which is the standard visual acuity test used in Cambridge University Hospital, Addenbrooke's Orthoptic Department

In the Sonksen logMAR Test (SLT), a single line of 4 letters separated from each other by 5 stroke-widths (or 1 optotype width), is contained within a box, separated from the letters also by 5 stroke-widths.

Recognition of target optotypes created by contrast-differences (second-order stimuli) is prone to greater crowding effects than is recognition of optotypes created by luminance-differences (first-order stimuli). This effect is present in normal vision, however even greater visual losses for contrast-defined targets, as well as stronger crowding effects, have been reported in amblyopia. By presenting a contrast-modulated (CM) target letter (H, O, T or V) surrounded by four other letters (U, A, L, C) placed 1 stroke-width away (in the modified Cambridge Crowding Test arrangement), this research aims to examine whether this second-order vision test will exaggerate differences between the eyes of amblyopic children, when compared to those measured in visually 'normal' children. The results will again be compared to those obtained with the Sonksen logMAR test (SLT), a first-order vision test, to compare their sensitivities to amblyopia detection.

Finally, crowding distance, the spatial distance over which crowding occurs, in normal foveal (central) vision is small (2-4 arcmin) and cannot be measured with current standard clinical optotypes due to their large size (5 arcmin for 0.0 logMAR acuity). To get around this difficulty, a new vision test was recently created to quantify the crowding distance or "critical spacing" of crowding . It uses a new "Pelli" font, which is much thinner horizontally than standard clinical fonts, allowing the optotypes to get closer to each other in physical space. This 'Crowding Distance Test' permits quantification of the critical spacing of crowding for the first time in a clinical population. The new "Pelli" font, each optotype appearing like tall skinny numbers, has already been trialled on 'visually normal' school-aged children, but not yet examined on children with greater sensitivity to visual crowding, i.e., amblyopes. The third vision test in the proposed research, will investigate whether or not "crowding distance" measures made in each eye, results in greater inter-ocular differences, leading to better detection of anisometropic and strabismic amblyopia than does the current clinical standard visual acuity test, the Sonksen logMAR test (SLT).

By using closer first-order target optotypes, second-order target optotypes, and quantifying crowding distance in paediatric populations, the ability to detect amblyopia and monitor amblyopia treatment, could be significantly improved for the first time since the 1960s. At that time crowding was first quantified in a clinical population of adult amblyopes and was subsequently incorporated into commercially available tests as best practice.

Study Type

Interventional

Enrollment (Anticipated)

48

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United Kingdom
    • Cambridgeshire
      • Cambridge, Cambridgeshire, United Kingdom, CB11PT
        • Anglia Ruskin University Eye Clinic

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

3 years to 11 years (Child)

Accepts Healthy Volunteers

No

Genders Eligible for Study

All

Description

Inclusion Criteria:

  • Test participants; Male and female 3 to 11-year-old children diagnosed by ACPOS clinicians as likely having amblyopia (strabismic or anisometropic). They will be tested following 6 weeks (or more) of refractive adaption.
  • Control Participants; Male and female 3 to 11-year-old children who have been falsely referred into the Hospital Eye Service (ACPOS) by the visual screening service, but have satisfactory visual functions, as per the national screening guidelines.
  • All participants must be able to complete the Sonsken logMAR Test (SLT) either verbally or via use of a matching card.

Exclusion Criteria:

  • Uncorrected refractive error.
  • The presence of any other vision limiting medical condition, not listed in the inclusion criteria.
  • Any prior or existing medical history of epilepsy or seizures.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Diagnostic
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Active Comparator: Control
Visual acuity tests on control participants
Diagnostic test: Visual acuity tests
Participants to have visual acuity tested with the three modified vision tests.
Other Names:
  • Contrast-modulated Cambridge Crowding test
  • Crowding Distance Test
  • Enhanced Cambridge Crowding test
Experimental: Amblyopic
Visual acuity tests on amblyopic participants.
Diagnostic test: Visual acuity tests
Participants to have visual acuity tested with the three modified vision tests.
Other Names:
  • Contrast-modulated Cambridge Crowding test
  • Crowding Distance Test
  • Enhanced Cambridge Crowding test

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Visual Acuity
Time Frame: Vision measured at the time of testing.
LogMAR
Vision measured at the time of testing.

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Anglia Ruskin University

Investigators

  • Study Director: Sarah Waugh, PhD, Anglia Ruskin University

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

January 1, 2019

Primary Completion (Actual)

May 31, 2021

Study Completion (Anticipated)

May 1, 2022

Study Registration Dates

First Submitted

April 4, 2018

First Submitted That Met QC Criteria

April 12, 2018

First Posted (Actual)

April 23, 2018

Study Record Updates

Last Update Posted (Actual)

July 21, 2021

Last Update Submitted That Met QC Criteria

July 20, 2021

Last Verified

July 1, 2021

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • FST/FREP/17/739

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

Undecided

IPD Plan Description

Pseudo-anonymised data to be uploaded to ARRO, the university data storage system.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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