1 John 1:1

Ὃ ἦν ἀ ἀρχῆς, ὃ ἀκηκόαμεν, ὃ ἑωράκαμεν τοῖς ὀφθαλμοῖς ἡμῶν, ὃ ἐθεασάμεθα καὶ αἱ χεῖρες ἡμῶν ἐψηλάφησαν περὶ τοῦ λόγου τῆς ζωῆς ἐθεασάμεθα καὶ αἱ χεῖρες ἡμῶν ἐψηλάφησαν περὶ τοῦ λόγου τῆς ζωῆς

That which was in the beginning, which we have heard, which we have seen with our eyes, which we looked upon and our hands touched concerning the word of life


 * Ὃ - relative pronoun is neuter. Why? Clearly later he is talking about the person of Jesus who, he has seen, heard, touched and so on. A few explanations found from the internet resources. John implied as his main topic "the eternal life" or "the life", which is a neuter entity. Christ is, of course, Life itself. Another explanation is that John is referring to the totality of his experience--"all that I have heard, seen...." about Jesus, about eternal life.... in this case neuter is appropriate.
 * ἀκηκόαμεν and ἑωράκαμεν are perfect tense. Things completed in the past but which have, as is obvious here, ongoing consequences or relevance to the present discourse
 * τοῖς ὀφθαλμοῖς - puzzled by the absence of a preposition? That's what dative is for. This is the instrumental use of the dative. By means of, with the eyes.
 * the next two verbs ἐθεασάμεθα and ἐψηλάφησαν are plain aorist indicative. Perhaps here John is referring to a one-off event like when he saw and touched Jesus when he first appeared to the disciples after his resurrection.