Complex sentence: In the 1850s Jäger made improvements to eye chart test types that were developed by Heinrich Kuechler (1811-1873), and in 1862 Dutch ophthalmologist Hermann Snellen introduced the popular "Snellen chart" for testing visual acuity.
Split into simpler sentences: In the 1850s Jäger made improvements to eye chart test types that were earlier developed by Heinrich Kuechler (1811-1873). In 1862 Dutch ophthalmologist Hermann Snellen introduced the popular "Snellen chart" for testing visual acuity.