That this question should have arisen at all is based on a misunderstanding of the nature and functioning of Renaissance art in general and Leonardo’s art in particular.
We should remember that Leonardo was drawing on his documented knowledge of rock crystal to devise a large sphere for Christ to hold, as an iconographical invention. He was not making a “portrait” of an actual sphere. Indeed spheres that large were not known at that time. Nor was he following all its optical consequences to their logical conclusion. I have been asked on many occasions why the drapery behind the sphere is not radically affected by what is in effect a large magnifying glass. The answer in a word is decorum; that is to say “pictorial good manners”. Leonardo observed many visual effects in the real world, such the blur of very fast-moving objects, that he would never have incorporated into paintings. He said that such extreme effects belonged to the world of “speculators” on natural phenomena rather than to the art of painting. He and other artists knew about refraction in water, but he certainly would not have portrayed Christ’s legs as optically bent in a Baptism. Leonardo’s paintings re-make nature not only accordance with natural law but also in obedience to the rules that governed functioning images for his patrons. He would not have disrupted the efficacy of the painting as a devotional image. His painting drew on his knowledge of optics and how the working of the eye (e.g. MS E) affected the clarity of objects at different distances, as in the Salvator Mundi, but they were not raw demonstrations of optical science, any more than they were stark demonstrations of anatomy. In the Mona Lisa for example he does not follow the visual implications of looking at a woman inside a balcony against a bright landscape, although he know precisely what the actual effect would have been.
Many of the things in the press (such as Leonardo never using a frontal pose) have been very poorly thought through. But de-bunking a $350 million painting gets column inches.
I have a book on the Salvator coming out next year with Robert Simon and Margaret Dalivalle. There is also a chapter in my personalised Living with Leonardo, published by Thames and Hudson in March.