I think what you are asking about is an orthoptist. Orthoptists are specialized ophthalmic technicians who measure deviations in muscle balance in eye examinations. Most of them work with pediatric and strabismus specialists to determine the type and degree of muscle imbalance in patients seeking treatment for strabismus. Done well, orthoptics--measurements by the orthoptist--are valuable to a busy strabismus practice, and provide important data to the ophthalmologist making management decisions for patients, including surgical planning.
The education usually requires some formal technical training, and there are ophthalmic technician training programs in many places in the country, but some orthoptists are also on-the-job trained.