The goal of this clinical trial is to see if a medicine called echothiophate iodide (Phospholine Iodide) can help treat children with refractory amblyopia. Amblyopia (also called lazy eye) is when one eye doesn't see as well as it should because the brain isn't using that eye correctly. Refractory amblyopia means a lazy eye that's very difficult to treat and it doesn't improve even after using common treatments, such as putting atropine eye drops in the stronger eye to encourage use of the weaker eye.

The main questions this study aims to answer are:

• Can adding echothiophate iodide eye drops help children who stopped improving with atropine alone start making progress again?
• Does using atropine and echothiophate iodide eye drops together work better for older children and adolescents who typically do not respond well to atropine alone?
• Besides improving eyesight, can echothiophate iodide eye drops also help with things like depth perception, seeing in crowded spaces, or noticing motion

Participants will be asked to:

• Participate in the study for a total of 14 weeks
• Attend four clinic visits
• Use atropine drops in the stronger eye nightly for a total 12 weeks
• Use of echothiophate iodide eye drops in the weaker eye in addition to atropine use in the stronger eye, if vision does not improve after 4 weeks of use of atropine alone in the stronger eye
• Upload weekly photos of the eyes
• Have a slit lamp exam performed at each visit
• Have Best Corrected Visual Acuity (BCVA) eye measurements taken at each visit.
• Have Optical Coherence Tomography Angiography (OCTA) images taken at at each visit.

Inclusion Criteria:

• Children/adolescents between 3 and <18 years old with amblyopia who are currently undergoing atropine treatment who are deemed to no longer be improving.
• Diagnosis of amblyopia associated with strabismus, anisometropia, or mixed types (as defined by previous PEDIG studies).
• Wearing appropriate spectacle correction based on cycloplegic refraction using PEDIG protocol recommendations.
• Currently undergoing atropine treatment (either 2x a week or every other day) with visual acuity in the amblyopic eye that has not improved with atropine treatment from participant's previous visit.
• Cycloplegic refraction that has been completed within 6 months of enrollment.
• Ability to measure visual acuity using standardized testing protocols.
• Visual acuity in the amblyopic eye 20/40 to 20/100. Visual acuity in the non-amblyopic eye 20/30 or better with intraocular difference greater than or equal to 2 lines.

Exclusion Criteria:

• Existing ocular conditions likely to interfere with treatment response (e.g., congenital cataract history, corneal opacities/scars, ptosis, retinal diseases).
• Neurologic or systemic conditions that impact vision.
• Severe developmental delays that might impact treatment adherence and outcome evaluation.
• Current use of prisms or bifocals.
• Active uveal inflammation or history of angle-closure glaucoma.
• Concurrent use of other anticholinesterase medications.
• Anticipated surgical procedures during the study period.
• Prior surgical interventions for ocular conditions that could interfere with study outcomes.
• Myopia with spherical equivalent >6D.
• Any contraindications to the components of the medicine to be used in the study