optanomai are two ways of spelling the same Greek word which Dr. Strong’s Concordance numbering system designates as #3700.
Revelation 1:7 — “…every eye shall see (optanomai) him….”
Matthew 24:30 — “…and they shall see (optanomai) the Son of man coming in the clouds of heaven with power and great glory.”
Mark 13:26 — “And then shall they see (optanomai) the Son of man coming in the clouds with great power and glory.”
Optanomai can mean literal seeing or mental perception. Its majority New Testament usage denotes a literal sight. However, it is also used to denote mental discernment.
Often the logic is used that if God wanted to teach a certain point in a verse of scripture, He would have used a Greek word that solely has that particular meaning. That is plainly incorrect. For example, God overruled the use of a Greek word in Rev. 20:10 that is translated
tormented and primarily means tormented. However, it can have significance of
testing or examining. The meaning of testing certainly harmonizes with the total teaching of scripture on the subject of the condition of the dead.
Why didn’t the Lord use a Greek word in Matthew 24:30 and Revelation 1:7 that solely means discern, that is, mental
 perception? This begs the question—why didn’t the Lord use a Greek word in Revelation 20:10 that solely means
examining instead of using a word that can also mean
Mark 4:12 clearly states that the scriptures were written purposely in parables and dark sayings so that only the faithful searchers would understand.
Often the Lord provides a key in the context or a related passage to assure us of the meaning of the word in question.
He has provided this key as to the meaning of
optanomai in a second advent setting. In our Lord’s Great Prophecy, the Greek word
eido (Strong’s #1492) is used a number of times (Matthew 24:33 and Mark 13:29) to solely denote mental perception. Then in a parallel passage, Luke 17:22,
eido (Strong’s #1492) and optanomai (Strong’s #3700) are used interchangeably.
Luke 17:22 — “And he said unto the disciples, The days will come, when ye shall desire to see (eido) one of the days of the Son of man, and ye shall not see (optanomai) it.”
Luke 17:22-37 is parallel to Matthew 24. This proves that
optanomai means mental perception in a Second Advent context.