Well, to begin with the army in 1071 would have been infinitely larger, as the Byzantine Empire in 1453 would have had very little resources to field an effective force.

The Byzantine Army in 1071 would have included large numbers of standing troops from central regiments called Tagmata, in addition to a militia drawn from farmers called Stratiotai who had military obligations, whereas in 1453 the soldierly would have consisted of a militia drawn from the population of Constantinople, contingents from foreigners settled in the city, the followings of aristocratic families and garrison forces from the Morea.

The Byzantine army in 1071 was an organized "national" force with light and heavy infantry and cavalry, a well-developed military doctrine and was generally trained and drilled to fight in pitched battles with standardized formations and equipment.

The army in 1453 wasn't really an army. It's organization varied according to different regions (such as the Morea, which functioned independently of Constantinople). There was very little drill, almost no standardization and was less of a formal state apparatus than it was a random collection of troops drawn from different sources.

Sources:

The Late Byzantine Army: Arms and Society, 1204-1453, By Mark Batusis.

Byzantium and Its Army, 284-1081, by Warren Treadgold.