Korsakoff's psychosis is diagnosed by -
Memory impairment in korsakoff's syndrome

Antegrade amnesia → New learning impaired.
Retrograde amnesia → (Loss of memory of past events)
Impaired recent memory
Relatively preserved remote memory
Impairment of explicit (conscious or declarative) type of long-term memory
Relatively preserved implicit (unconscious or non-declarative) type of long-term memory

Don’t get confuse remote memory with long-term memory. All remote memories are long-term memories. However, not all
long-term memories are remote memories. Read below:-

Recent memory includes both short-term (immediate) and long-term (delayed) memory. In Korsakoff's syndrome, recent memory is impaired, that means both short term and long term memories are involved. However, only long-term memory of recent past involved (say, for example, 20-30 minutes or 1 hour).
Remote memory is long-term memory of more distant past, which is not impaired in Korsakoff's syndrome. Therefore, long-term memory of the distant past (say for example, before the onset of illness) is not impaired.
Peripheral neuropathy
Visual hallucination
Impairment of long term memory
Seizures
Impairment of long term memory