New Visual Acuity and Crowding Tests for Better Detection of Amblyopia

NCT ID: NCT03505606

Last Updated: 2024-10-21

Basic Information

• Recruitment Status: COMPLETED
• Clinical Phase: NA
• Total Enrollment: 76 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2019-01-01
• Study Completion Date: 2021-07-01

Brief Summary

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).

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.

Conditions

Amblyopia

Study Design

• Allocation Method: RANDOMIZED
• Intervention Model: PARALLEL
• Primary Study Purpose: DIAGNOSTIC
• Blinding Strategy: NONE

Study Groups

Control

Visual acuity tests on control participants

Group Type: ACTIVE_COMPARATOR

Visual acuity tests

Intervention Type: DIAGNOSTIC_TEST

Participants to have visual acuity tested with the three modified vision tests.

Strabismic/mixed amblyopes

Visual acuity tests on strabismic/mixed amblyopic participants.

Group Type: EXPERIMENTAL

Visual acuity tests

Intervention Type: DIAGNOSTIC_TEST

Participants to have visual acuity tested with the three modified vision tests.

Anisometropic amblyopes

Visual acuity tests on anisometropic amblyopic participants.

Group Type: EXPERIMENTAL

Visual acuity tests

Intervention Type: DIAGNOSTIC_TEST

Participants to have visual acuity tested with the three modified vision tests.

Interventions

Visual acuity tests

Participants to have visual acuity tested with the three modified vision tests.

Intervention Type: DIAGNOSTIC_TEST

Other Intervention Names

Contrast-modulated Cambridge Crowding test; Crowding Distance Test; Enhanced Cambridge Crowding test

Eligibility Criteria

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.

• Any prior or existing medical history of epilepsy or seizures.

Exclusion Criteria

• Uncorrected refractive error.

• Minimum Eligible Age: 3 Years
• Maximum Eligible Age: 11 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: Yes

Sponsors

Anglia Ruskin University

OTHER

Sponsor Role: lead

Responsible Party

Responsibility Role: SPONSOR

Principal Investigators

Sarah Waugh, PhD

Role: STUDY_DIRECTOR

University of Huddersfield

Locations

Anglia Ruskin University Eye Clinic

Cambridge, Cambridgeshire, United Kingdom

Countries

United Kingdom

References

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Reference Type: BACKGROUND

PMID: 18217825 (View on PubMed)

Chung ST, Li RW, Levi DM. Crowding between first- and second-order letters in amblyopia. Vision Res. 2008 Mar;48(6):788-98. doi: 10.1016/j.visres.2007.12.011. Epub 2008 Jan 31.

Reference Type: BACKGROUND

PMID: 18241910 (View on PubMed)

Danilova MV, Bondarko VM. Foveal contour interactions and crowding effects at the resolution limit of the visual system. J Vis. 2007 Nov 27;7(2):25.1-18. doi: 10.1167/7.2.25.

Reference Type: BACKGROUND

PMID: 18217840 (View on PubMed)

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Reference Type: BACKGROUND

PMID: 14065335 (View on PubMed)

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Reference Type: BACKGROUND

PMID: 24071956 (View on PubMed)

Hairol MI, Formankiewicz MA, Waugh SJ. Foveal visual acuity is worse and shows stronger contour interaction effects for contrast-modulated than luminance-modulated Cs. Vis Neurosci. 2013 May;30(3):105-20. doi: 10.1017/S0952523813000102. Epub 2013 Apr 25.

Reference Type: BACKGROUND

PMID: 23731769 (View on PubMed)

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Reference Type: BACKGROUND

PMID: 22824242 (View on PubMed)

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Reference Type: BACKGROUND

PMID: 26878696 (View on PubMed)

Siderov J, Waugh SJ, Bedell HE. Foveal contour interaction for low contrast acuity targets. Vision Res. 2013 Jan 25;77:10-3. doi: 10.1016/j.visres.2012.11.008. Epub 2012 Nov 29.

Reference Type: BACKGROUND

PMID: 23200866 (View on PubMed)

Song S, Levi DM, Pelli DG. A double dissociation of the acuity and crowding limits to letter identification, and the promise of improved visual screening. J Vis. 2014 May 5;14(5):3. doi: 10.1167/14.5.3.

Reference Type: BACKGROUND

PMID: 24799622 (View on PubMed)

Wong EH, Levi DM, McGraw PV. Is second-order spatial loss in amblyopia explained by the loss of first-order spatial input? Vision Res. 2001 Oct;41(23):2951-60. doi: 10.1016/s0042-6989(01)00189-4.

Reference Type: BACKGROUND

PMID: 11704234 (View on PubMed)

Wong EH, Levi DM, McGraw PV. Spatial interactions reveal inhibitory cortical networks in human amblyopia. Vision Res. 2005 Oct;45(21):2810-9. doi: 10.1016/j.visres.2005.06.008.

Reference Type: BACKGROUND

PMID: 16040080 (View on PubMed)

Provided Documents

Document Type: Study Protocol, Statistical Analysis Plan, and Informed Consent Form

View Document

Other Identifiers

FST/FREP/17/739

Identifier Type: -

Identifier Source: org_study_id