Condition category
Eye Diseases
Date applied
Date assigned
Last edited
Retrospectively registered
Overall trial status
Recruitment status
No longer recruiting
Publication status

Plain English Summary

Not provided at time of registration

Trial website

Contact information



Primary contact

Prof Bruce Evans


Contact details

Institute of Optometry
56-62 Newington Causeway
United Kingdom
+44 (0)20 7407 4183

Additional identifiers

EudraCT number number

Protocol/serial number


Study information

Scientific title


Study hypothesis

Amblyopia has a prevalence of 1-4% and is the leading cause of monocular visual loss in the age group 20-70 years (Simons, 1996) . Since AD 900 (Thabit Ibn Qurrah, 900), amblyopia has been treated by occluding the eye with better acuity. Although the lack of randomised controlled trials (RCTs) has been criticised (Moseley et al., 1995), this form of treatment is widely accepted clinically as long as the patient is treated within the so-called 'sensitive period' or 'critical period' of relatively high neural plasticity (Nelson, 1989).

Evans et al. (1999) carried out a clinical audit of Mallett's IPS treatment for amblyopia. The mean improvement was two lines of the Snellen chart and 100% of this improvement had occurred after 5 treatment sessions.

The purpose of the current study is to compare the Mallett IPS treatment with a placebo, using a randomised double-masked protocol.

Ethics approval

Added 28 July 2008:
Received from City University and Institute of Optometry .

Study design

Double-masked randomised controlled trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting

Not specified

Trial type

Not Specified

Patient information sheet

Full verbal and written information is provided to each participant and is available on request.


Eye Diseases: Amblyopia


Patients meeting strict diagnostic criteria for amblyopia are randomly allocated to an experimental and a control group. The control treatment (modified CAM) was developed to give subjects the same degree of time, attention, and use of 'high-tech' equipment as the IPS treatment, but to have no features which are likely to generate a treatment effect. A two-interval 26 alternative forced choice method is used to measure LogMAR acuities on three consecutive weekly occasions before treatment. Subjects are then treated for 6 weeks and, a week after the final treatment, acuities are again measured but by a researcher who does not know which treatment the subjects have received.

Intervention type



Not Specified

Drug names

Primary outcome measure

A table of findings will be drawn up describing the characteristics of the participants in the experimental group (e.g., age of onset, type of amblyopia, age at treatment) and participants will be ranked in this table in terms of their improvement in VA following treatment (based on their own z-score of improvement). The data will be inspected to see if there are any trends whereby particular types or sub-groups of amblyopia improve with IPS.

Secondary outcome measures

Not provided at time of registration

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

Subjects will be aged 10-65 years. Visual acuity between 6/9 and 6/36 in the amblyopic eye and 6/6 or better in the good eye and where the amblyopia is the result of strabismus or anisometropia. Participants will meet the following selection criteria:

1. No personal history of epilepsy.
2. Willing to attend the Institute of Optometry for the three pre-treatment assessments, six treatment sessions, the post treatment assessment, and the follow-up assessment.
3. Unilateral amblyopia with visual acuity better than 6/36 but worse than 6/9 in the amblyopic eye and 6/6 or better in the non-amblyopic eye.
4. Amblyogenic factor: amblyopic eye is either strabismic or has at least 1D more hypermetropia or 2D more astigmatism than the non-amblyopic eye.
5. No ophthalmoscopically detectable anomalies of fundus or defects of the visual pathway. This will be taken to mean no clinically significant departure from a normal ophthalmoscopic appearance and 30 degrees visual fields (static perimetry) within normal limits.
6. Patients must be at least 10 years old and have signed the informed consent form, or have this signed by a parent or guardian if under 16 years old.
7. No history of strabismus or other cause of reduced visual acuity (e.g., cataract) in first two years of life.
8. Subjects must have had a recent (within the last 1 year) eye examination and must be wearing the appropriate refractive correction. The cost of this appointment and of any refractive correction will have to be met by the participant. Anisometropic participants will be encouraged to wear contact lenses as this has been shown to be the best option to minimise aniseikonia (Winn et al., 1988). Participants must be adapted to any refractive correction, having worn the correction for at least four months (Stewart et al., 2004).

Participant type


Age group



Not Specified

Target number of participants

Sample size calculations indicate that the study will be continued until 32 participants have finished in each group.

Participant exclusion criteria

1. Personal history of epilepsy.
2. Unilateral amblyopia with visual acuity worse than 6/36 or better than 6/9 in the amblyopic eye and 6/9 or worse in the non-amblyopic eye.
3. Amblyogenic factor: cases where amblyopic eye has less than 1D more hypermetropia or less than 2D more astigmatism than the non-amblyopic eye.
4. Ophthalmoscopically detectable anomalies of fundus or defects of the visual pathway.
5. Patients under 10 years old
6. History of strabismus or other cause of reduced visual acuity (eg cataract) in first two years of life

Recruitment start date


Recruitment end date



Countries of recruitment

United Kingdom

Trial participating centre

Institute of Optometry
United Kingdom

Sponsor information


Department of Health

Sponsor details

Richmond House
79 Whitehall
United Kingdom
+44 (0)20 7307 2622

Sponsor type




Funder type


Funder name

City Eye Clinic (EYENET) (UK) NHS R&D Support Funding

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

Not provided at time of registration

Intention to publish date

Participant level data

Not provided at time of registration

Basic results (scientific)

Publication list

1. 2011 results in

Publication citations

  1. Results

    Evans BJ, Yu CS, Massa E, Mathews JE, Randomised controlled trial of intermittent photic stimulation for treating amblyopia in older children and adults., Ophthalmic Physiol Opt, 2011, 31, 1, 56-68, doi: 10.1111/j.1475-1313.2010.00801.x.

Additional files

Editorial Notes