A full description of the operation is given by Paul:
‘We measure off a nucleus’ breadth (ὅσον πυρηνομήλης) from the part called the iris and in the direction of the outer canthus, then mark with the olivary end of the couching needle (πυρῆνι παρακεντηρίου) the place to be perforated. If it is in the left eye, we work with the right hand, and vice versa. Bringing round the pointed end of the perforator, which is round at the tip (καὶ ἀναστρέψαντες τὴν ἀκμὴν στρογγύλην κατὰ τὸ πέρας ὑπάρχουσαν τοῦ κεντηρίου), we push it firmly through at the part which was marked out until we come to an empty space. The depth of the perforation should be as great as the distance of the cornea from the iris. Then raising the needle to the apex of the cataract (the bronze of it is plainly visible through the transparent part of the cornea) we depress the cataract to the underlying parts. After the couching of the cataract we gently extract the needle with a rotatory movement’ (VI. xxi).
It will be seen from Paul’s vivid description that the couching instrument consisted of a handle with a nucleus at one end, to measure off the spot at which to perforate, and a needle at the other. We saw that the outfit of the oculist Severus contained one such instrument ([Pl. XVI, fig. 2]). The same combination is not infrequently met with. In the Museum at Aarau there are four from the station at Vindonissa. I have one in my collection which is interesting as showing a screw thread for fitting on a cover to protect the needle ([Pl. XVI, fig. 7]). It was found in Bedfordshire. It reminds one very strongly of the couching needle figured by Paré. Other handled needles were used in eye work as cauteries. Of trichiasis Celsus says (VII. vii):
Si pili nati sunt qui non debuerunt, tenuis acus ferrea ad similitudinem spathae lata in ignem coniicienda est: deinde candens, sublata palpebra sic ut eius perniciosi pili in conspectum curantis veniant, sub ipsis pilorum radicibus ab angulo immittenda est ut ea tertiam partem palpebrae transsuat; deinde iterum, tertioque usque ad alterum angulum; quo fit ut omnes pilorum radices adustae emoriantur.
Ophthalmic Probe.
Greek, ὀφθαλμικὴ μήλη.
In Hippocrates (ii. 100) we find an ophthalmic probe mentioned.
Λεπίδος μῆλαι τρεῖς τῷ πλατεῖ καὶ ἀλήτου σητανίου κόλλης, πάντα ταῦτα λεῖα τρίψας, καταπότια ποιήσας δίδου.
‘Of squama aeris three times the full of a specillum and [as much] of the gluten of wheat. Levigate all up fine, form into pills and administer.’
Galen in his Lexicon explains that μῆλαι τρεῖς τῷ πλατεῖ means τῷ κυαθίσκῳ ὀφθαλμικῆς μήλης. This is the only mention which we have of a special ophthalmic probe with scoop. In applying medicaments to the eye with a probe whenever any variety of probe is mentioned it is always the ear specillum which is named. It seems most likely that either the ear specillum or some variety of it is referred to here. It may have had a nucleus for applying medicaments at one end and a scoop at the other.