The goal of this clinical trial is to learn whether adding noninvasive brain stimulation to augmented reality-based vision therapy can improve vision in adults aged 18 to 40 years with unilateral anisometropic amblyopia, commonly called "lazy eye." Anisometropic amblyopia develops during childhood when the two eyes have different focusing powers and the brain relies more on one eye than the other.
The main questions this study aims to answer are:
* Does active high-definition transcranial direct current stimulation (HD-tDCS) improve best-corrected visual acuity in the amblyopic eye and depth perception more than sham stimulation? * Does the combined treatment improve contrast sensitivity, suppression between the eyes, and measures of retinal and visual brain function?
All participants will receive the same augmented reality-based dichoptic therapy. This therapy presents different visual information to each eye and lowers the contrast seen by the stronger eye. This gives the weaker, amblyopic eye a visual advantage and encourages both eyes to work together while participants carry out normal daily activities.
During the first 2 weeks, participants will also receive either active HD-tDCS or sham stimulation immediately before the augmented reality therapy. Active HD-tDCS delivers a weak electrical current through small electrodes placed on the scalp. Sham stimulation uses the same equipment and procedures, but the current is applied only briefly at the beginning. Comparing the two groups will help researchers determine whether active brain stimulation provides additional benefits beyond those of augmented reality therapy alone.
Participants will:
* Complete 40-minute augmented reality therapy sessions four times per week for 10 weeks. * Receive eight 20-minute sessions of active or sham HD-tDCS during the first 2 weeks, immediately before the augmented reality therapy. * Attend assessment visits before treatment, after 2 weeks, and after 10 weeks. These visits will include vision tests, retinal imaging, tests of retinal function, and brain imaging.
Age between 18 and 40 years.
Diagnosis of anisometropic amblyopia.
Unilateral amblyopia with an interocular difference of at least 2 lines in best-corrected visual acuity, with visual acuity worse than 20/32 in the worse-seeing eye.
Any type of amblyopia other than anisometropic amblyopia.
Bilateral amblyopia.
Ophthalmological or neuro-ophthalmological disease other than amblyopia.
Neurological disease.
Parallel
Active High-Definition Transcranial Direct Current Stimulation
DeviceActive high-definition transcranial direct current stimulation will be delivered using a Soterix MxN-33 stimulator and a 4 × 1 electrode montage targeting the primary visual cortex. The central anodal electrode will be positioned at Oz, with four return electrodes positioned at PO3, PO4, PO7, and PO8. A current of 2.0 mA will be delivered for 20 minutes, including a 30-second ramp-up period at the beginning and a 30-second ramp-down period at the end of stimulation. Participants will receive eight sessions during the first 2 weeks, immediately before the augmented reality-based dichoptic therapy.
Sham High-Definition Transcranial Direct Current Stimulation
DeviceSham high-definition transcranial direct current stimulation will use the same stimulator, electrode montage, electrode positions, and session duration as active stimulation. The current will be ramped up over 30 seconds at the beginning of the session and then ramped down over 30 seconds, with no sustained current delivered during the remainder of the session. Participants will receive eight 20-minute sessions during the first 2 weeks, immediately before the augmented reality-based dichoptic therapy.
Augmented Reality-Based Dichoptic Therapy
DeviceAugmented reality-based dichoptic therapy will be delivered using a Meta Quest 3 headset. Participants will complete 40-minute sessions four times per week for 10 weeks. The therapy presents different visual information to each eye and reduces the contrast presented to the stronger eye, giving the amblyopic eye a visual advantage and encouraging both eyes to work together. Visual acuity in the amblyopic eye will be assessed within the headset to guide adjustment of the contrast presented to the stronger eye. The augmented reality environment allows participants to interact with their real surroundings and perform everyday activities during therapy.
Change From Baseline in Best-Corrected Visual Acuity of the Amblyopic Eye at Week 2
Best-corrected visual acuity of the amblyopic eye will be assessed monocularly using a standardized ETDRS chart and recorded as the number of letters correctly identified. Higher ETDRS letter scores indicate better visual acuity. Change from baseline will be calculated as the Week 2 letter score minus the baseline letter score. A positive change indicates an improvement in visual acuity.
Change From Baseline in Best-Corrected Visual Acuity of the Amblyopic Eye at Week 10
Best-corrected visual acuity of the amblyopic eye will be assessed monocularly using a standardized ETDRS chart and recorded as the number of letters correctly identified. Higher ETDRS letter scores indicate better visual acuity. Change from baseline will be calculated as the Week 10 letter score minus the baseline letter score. A positive change indicates an improvement in visual acuity.
Change From Baseline in Near Stereoacuity at Week 2
Near stereoacuity will be assessed binocularly using a graded circles stereotest with polarized glasses and recorded in seconds of arc. Measurable stereoacuity ranges from 400 to 20 seconds of arc. Lower values indicate better stereoacuity. Change from baseline will be calculated as the Week 2 value minus the baseline value. A negative change indicates an improvement. Participants unable to identify the largest disparity will be classified as having no measurable stereoacuity.
Change From Baseline in Near Stereoacuity at Week 10
Near stereoacuity will be assessed binocularly using a graded circles stereotest with polarized glasses and recorded in seconds of arc. Measurable stereoacuity ranges from 400 to 20 seconds of arc. Lower values indicate better stereoacuity. Change from baseline will be calculated as the Week 10 value minus the baseline value. A negative change indicates an improvement. Participants unable to identify the largest disparity will be classified as having no measurable stereoacuity.
Change From Baseline in Interocular Suppression at Week 2
Interocular suppression will be assessed under binocular viewing conditions using a standardized suppression test. The outcome will be the filter level at which binocular perception changes. Change from baseline will be calculated as the Week 2 value minus the baseline value.
Change From Baseline in Interocular Suppression at Week 10
Interocular suppression will be assessed under binocular viewing conditions using a standardized suppression test. The outcome will be the filter level at which binocular perception changes. Change from baseline will be calculated as the Week 10 value minus the baseline value.
Change From Baseline in Static Achromatic Contrast Sensitivity of the Amblyopic Eye at Week 2
Static achromatic contrast sensitivity will be assessed monocularly in the amblyopic and fellow eyes using the MonCV3 system (Metrovision). Sinusoidal gratings will be presented at a temporal frequency of 0 Hz and at spatial frequencies of 0.55, 1.1, 2.2, 3.4, 7.1, and 14.2 cycles per degree. Results will be recorded in decibels (dB) separately for each eye and spatial frequency, with higher values indicating better contrast sensitivity. Change from baseline will be calculated as the Week 2 value minus the baseline value. A positive change indicates improvement.
Change From Baseline in Static Achromatic Contrast Sensitivity in the Amblyopic and Fellow Eyes at Week 10
Static achromatic contrast sensitivity will be assessed monocularly in the amblyopic and fellow eyes using the MonCV3 system (Metrovision). Sinusoidal gratings will be presented at a temporal frequency of 0 Hz and at spatial frequencies of 0.55, 1.1, 2.2, 3.4, 7.1, and 14.2 cycles per degree. Results will be recorded in decibels (dB) separately for each eye and spatial frequency, with higher values indicating better contrast sensitivity. Change from baseline will be calculated as the Week 10 value minus the baseline value. A positive change indicates improvement.
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Polytechnic Institute of Porto
Lead sponsor
University of Coimbra
Collaborator
