A. If the cor’nea be too convex (or projecting), the person must wear double concave glasses, to counteract it.
Q. What is meant by “double concave glasses?”
A. Glasses hollowed in on both sides.
The figure A is double concave, or concave on both sides.
Q. What is meant by the “image of objects being reflected before it reaches the ret’ina?”
A. If the cor’nea be too convex, the image of a distant object is reflected (on the vitreous humours of the eye) before it reaches the ret’ina.
Thus the image is reflected at DE, instead of on ABC (the ret'ina).