This question has been on my mind for a while now. In Western Europe throughout the 14th and 15th centuries we see the development of increasingly protective armor, mainly in the form of steel or iron plate. I know that the development of the klivanion mainly occurred during the High Middle Ages, but can't find much information as to how Byzantine armor progressed from here.
Do we see advancements that parallel the advent of plate armor in Western Europe, either through the adoption of plate or a refinement of lamellar armor, or did the empire's decline simply halt technological progress in this area? Would a wealthy Byzantine cataphract, for instance, equipped with state-of-the-art armor around 1453 have the same defensive capabilities as a contemporary French man-at-arms wearing the western equivalent?
It's hard to talk specifically about Byzantine armor in the late period. This is because the army a) had an increasing reliance on foreign troops and b) the archaeological evidence we do have is dominated by foreign style equipment (Turk or Frank). The army would have used chainmail with leather and iron lamellar supplements. The Byzantines did not adopt plate armor in a large scale into their armies (partly due no doubt to the economic situation and geographical location of the Empire in the 1400s).
The wealthiest of soldiers would no doubt have been able to afford the style of protection of French men-at-arms, but Bartusis doesn't find much evidence of the adoption of iron plate. That said, I'd be surprised if some plate protection didn't replace the leather and lamellar supplements in the heaviest soldiers. If they did, however, it would have been imported from the west (not developed in the Empire).
I'm no expert on the subject, but my info here comes from: The Late Byzantine Army: Arms and Society, 1204-1453 by Mark Bartusis. I welcome corrections if the info is out of date.