The orthoptic examinations are performed by an orthoptist. An orthoptist is a person who performs certain examinations in an opthalmological clinic. The job concerns the examination of strabismic patients, testing for diplopia and treating amblyopia.
The main part of the patients tend to be children. The visual acuity can be judged in babies already! The BVA (Berufsverband der Augenärzte) and the BOD (Berufsverband der Orthoptistinnen Deutschlands e.V.) advises as to when a thorough orthoptic and ophthalmological examination should be performed:

a.s.a.p.

With children that show abnormalities like ptosis (drooping eye) corneal opacities, cataract, pupillary anomalies, nystagmus or any suspection of glaucoma

At the age of 6 months up to one year

With all children with an increased risk of strabismus and hereditary ailments, i.e. in short prematures and those genetically prone

Preferably at the age of 2 till 3 at the most

All other children even those that seem normal in respect of the early discoverage of microstrabismus (small angle strabismus) and higher grades of refractive errors.

One cannot discover the late onset type of strabismus (at e.g. age four) with this type of screening. If there is any suspicion a repeated examination will be necessary at the age of 4 -5 years.