ἔστι δὴ οὖν δεῦρο ὁ πᾶς ἥκων λόγος περὶ τῆς τετάρτης μανίας—ἣν ὅταν τὸ τῇδέ τις ὁρῶν κάλλος, τοῦ ἀληθοῦς ἀναμιμνῃσκόμενος, πτερῶταί τε καὶ ἀναπτερούμενος προθυμούμενος ἀναπτέσθαι, ἀδυνατῶν δέ, ὄρνιθος δίκην βλέπων ἄνω, τῶν κάτω δὲ ἀμελῶν, αἰτίαν ἔχει ὡς μανικῶς διακείμενος
Our whole discussion having arrived at this point, is about the fourth kind of madness, which is the cause of his being mad, for whenever he sees mundane beauty, he recollects the true one and starts growing wings; becoming fully-fledged, he strives to fly up; but unable to do so, gazes upwards like a bird neglecting what is below.
I think that there is no anacoluthon here as Yunis suggest but αἰτίαν is in apposition to ἣν.