§5.1#3τὸ μὲν γὰρ γλαύκωμα γίνεται μᾶλλον τοῖς γλαυκοῖς, οἱ δὲ νυκτάλωπες καλούμενοι τοῖς μελανοφθάλμοις.
For cataracts occur more in those with blue eyes, and the so-called night-blindness in those with dark eyes.
ἔστι δὲ τὸ μὲν γλαύκωμα ξηρότης τις μᾶλλον τῶν ὀμμάτων, διὸ καὶ συμβαίνει μᾶλλον γηράσκουσιν· ξηραίνεται γάρ, ὥσπερ καὶ τὸ ἄλλο σῶμα, καὶ ταῦτα τὰ μόρια πρὸς τὸ γῆρας·
And cataracts are rather a kind of dryness of the eyes, wherefore it also happens more to those who are growing old; for these parts, like the rest of the body, dry up towards old age.
ὁ δὲ νυκτάλωψ ὑγρότητος πλεονασμός, διὸ τοῖς νεωτέροις γίνεται μᾶλλον· ὑγρότερος γὰρ ὁ ἐγκέφαλος ὁ τούτων.
But night-blindness is an excess of fluid, wherefore it occurs more to younger individuals; for their brain is more fluid.
ἡ δὲ μέση τοῦ πολλοῦ καὶ τοῦ ὀλίγου ὑγροῦ βελτίστη ὄψις· οὔτε γὰρ ὡς ὀλίγη οὖσα διὰ τὸ ταράττεσθαι ἐμποδίζει τὴν τῶν χρωμάτων κίνησιν, οὔτε διὰ πλῆθος παρέχει δυσκινησίαν.
But the mean between much and little fluid is the best sight; for neither, being little, does it disrupt and hinder the movement of colors because of being easily disturbed, nor does it cause difficulty of movement because of abundance.
οὐ μόνον δὲ τὰ εἰρημένα αἴτια τοῦ ἀμβλὺ ἢ ὀξὺ ὁρᾶν, ἀλλὰ καὶ ἡ τοῦ δέρματος φύσις τοῦ ἐπὶ τῇ κόρῃ καλουμένῃ.
And not only are the aforementioned things the causes of seeing dimly or keenly, but also the nature of the skin over the so-called pupil.
δεῖ γὰρ αὐτὸ διαφανὲς εἶναι, τοιοῦτον δ᾽ ἀναγκαῖον εἶναι τὸ λεπτὸν καὶ λευκὸν καὶ ὁμαλὸν δ᾽ ὅπως μὴ ἐπισκιάζῃ ῥυτιδούμενον (καὶ γὰρ διὰ τοῦθ᾽ οἱ γέροντες οὐκ ὀξὺ ὁρῶσιν· ὥσπερ γὰρ καὶ τὸ ἄλλο δέρμα, καὶ τὸ τοῦ ὄμματος ῥυτιδοῦταί τε καὶ παχύτερον γίνεται γηράσκουσιν), λευκὸν δὲ διὰ τὸ τὸ μέλαν μὴ εἶναι διαφανές· αὐτὸ γὰρ τοῦτ᾽ ἐστὶ τὸ μέλαν, τὸ μὴ διαφαινόμενον.
For it must be transparent, and it is necessary for such a thing to be thin and white and smooth, so that it may not cast a shadow by being wrinkled (for indeed because of this old men do not see keenly; for like the rest of the skin, that of the eye also wrinkles and becomes thicker as they grow old), and it must be white because the black is not transparent; for the black is itself this very thing, that which is not seen through.
διόπερ οὐδ᾽ οἱ λαμπτῆρες δύνανται φαίνειν, ἐὰν ὦσιν ἐκ τοιούτου δέρματος.
Wherefore not even lamps can shine if they are made of such skin.
ἐν μὲν οὖν τῷ γήρᾳ καὶ ταῖς νόσοις διὰ ταύτας τὰς αἰτίας οὐκ ὀξὺ βλέπουσι, τὰ δὲ παιδία δι᾽ ὀλιγότητα τοῦ ὑγροῦ γλαυκὰ φαίνεται τὸ πρῶτον.
In old age, then, and in diseases they do not see keenly because of these causes, but children's eyes appear blue at first because of the smallness of the fluid.
ἑτερόγλαυκοι δὲ γίνονται μάλιστα οἱ ἄνθρωποι καὶ οἱ ἵπποι διὰ τὴν αὐτὴν αἰτίαν δι᾽ ἥνπερ ὁ μὲν ἄνθρωπος πολιοῦται μόνος, τῶν δ᾽ ἄλλων ἵππος μόνον ἐπιδήλως γηράσκων λευκαίνεται τὰς τρίχας.
And men and horses especially become wall-eyed because of the very same cause for which man alone turns gray, and of the other animals, the horse alone obviously turns white in its hair as it grows old.
ἥ τε γὰρ πολιότης ἀσθένειά τίς ἐστι τοῦ ὑγροῦ τοῦ ἐν τῷ ἐγκεφάλῳ καὶ ἀπεψία καὶ ἡ γλαυκότης· τὸ γὰρ λίαν λεπτὸν ἢ λίαν παχὺ τὴν αὐτὴν ἔχει δύναμιν τὸ μὲν τῷ ὀλίγῳ τὸ δὲ τῷ πολλῷ ὑγρῷ.
For grayness is a kind of weakness of the fluid in the brain and indigestion, and so is blueness; for the excessively thin or excessively thick has the same power, the one as the small, the other as the large amount of fluid.
ὅταν οὖν μὴ δύνηται ἀπαρτίσαι ἡ φύσις ὁμοίως ἢ πέψασα τὸ ἐν ἀμφοτέροις ὑγρὸν ἢ μὴ πέψασα, ἀλλὰ τὸ μὲν τὸ δὲ μή, τότε συμβαίνει γίνεσθαι ἑτερογλαύκους.
When, therefore, nature cannot finish them equally, either by concocting the fluid in both or by not concocting it, but concocting the one and not the other, then it happens that they become wall-eyed.
περὶ δὲ τοῦ τὰ μὲν ὀξυωπὰ εἶναι τῶν ζῴων τὰ δὲ μή, δύο τρόποι τῆς αἰτίας εἰσίν.
And concerning animals being sharp-sighted or not, there are two ways of the cause.
διχῶς γὰρ λέγεται τὸ ὀξὺ σχεδόν, καὶ περὶ τὸ ἀκούειν καὶ τὸ ὀσφραίνεσθαι ὁμοίως τοῦτ᾽ ἔχει.
For 'sharp' is said in almost two ways, and it is the same way also concerning hearing and smelling.
λέγεται γὰρ ὀξὺ ὁρᾶν ἓν μὲν τὸ πόρρωθεν δύνασθαι ὁρᾶν, ἓν δὲ τὸ τὰς διαφορὰς ὅτι μάλιστα διαισθάνεσθαι τῶν ὁρωμένων.
For to see keenly is said in one way as being able to see from afar, and in another as perceiving as much as possible the differences of the things seen.
ταῦτα δ᾽ οὐχ ἅμα συμβαίνει τοῖς αὐτοῖς.
And these do not happen to the same individuals at the same time.
ὁ γὰρ αὐτὸς ἐπηλυγισάμενος τὴν χεῖρα ἢ δι᾽ αὐλοῦ βλέπων τὰς μὲν διαφορὰς οὐθὲν μᾶλλον οὐδ᾽ ἧττον κρίνει τῶν χρωμάτων, ὄψεται δὲ πορρώτερον.
For the same person, having shaded his eye with his hand or looking through a tube, judges the differences of colors no more and no less, but will see further.
οἱ γοῦν ἐκ τῶν ὀρυγμάτων καὶ φρεάτων ἐνίοτε ἀστέρας ὁρῶσιν.
At any rate, those looking out from trenches and wells sometimes see the stars.
ὥστ᾽ εἴ τι τῶν ζῴων ἔχει μὲν προβολὴν τοῦ ὄμματος πολλήν, τὸ δ᾽ ἐν τῇ κόρῃ ὑγρὸν μὴ καθαρὸν μηδὲ σύμμετρον τῇ κινήσει τῇ θύραθεν, μηδὲ τὸ ἐπιπολῆς δέρμα λεπτόν, τοῦτο περὶ μὲν τὰς διαφορὰς οὐκ ἀκριβώσει τῶν χρωμάτων, πόρρωθεν δ᾽ ἔσται ὁρατικόν, ὥσπερ εἰ καὶ ἐγγύθεν, μᾶλλον τῶν τὸ μὲν ὑγρὸν καθαρὸν ἐχόντων καὶ τὸ σκέπασμα αὐτοῦ, μὴ ἐχόντων δ᾽ ἐπισκύνιον πρὸ τῶν ὀμμάτων μηθέν.
So that if any animal has a large projection of the eye, but the fluid in the pupil is not pure nor proportionate to the movement from without, nor is the skin on the surface thin, this animal will not be accurate about the differences of colors, but will be able to see from afar, just as if from near, more than those which have the fluid and its covering pure, but do not have any eyebrow-projection in front of their eyes.
τοῦ μὲν γὰρ οὕτως ὀξὺ ὁρᾶν ὥστε διαισθάνεσθαι τὰς διαφοράς, ἐν αὐτῷ τῷ ὄμματί ἐστιν ἡ αἰτία· ὥσπερ γὰρ ἐν ἱματίῳ καθαρῷ καὶ αἱ μικραὶ κηλῖδες ἔνδηλοι γίνονται, οὕτως καὶ ἐν τῇ καθαρᾷ ὄψει καὶ αἱ μικραὶ κινήσεις δῆλαι καὶ ποιοῦσιν αἴσθησιν.
For of seeing so keenly as to perceive the differences, the cause is in the eye itself; for just as on a clean garment even small spots become obvious, so also in clean sight even small movements are obvious and produce sensation.
τοῦ δὲ τὰ πόρρωθεν ὁρᾶν καὶ τὴν ἀπὸ τῶν πόρρωθεν ὁρατῶν ἀφικνεῖσθαι κίνησιν ἡ θέσις αἰτία τῶν ὀφθαλμῶν· τὰ μὲν γὰρ ἐξόφθαλμα οὐκ εὐωπὰ πόρρωθεν, τὰ δ᾽ ἐντὸς ἔχοντα τὰ ὄμματα ἐν κοίλῳ κείμενα ὁρατικὰ τῶν πόρρωθεν διὰ τὸ τὴν κίνησιν μὴ σκεδάννυσθαι εἰς ἀχανὲς ἀλλ᾽ εὐθυπορεῖν.
But of seeing things from afar and of the movement from distant visible things reaching the eye, the cause is the position of the eyes; for those with prominent eyes do not see well from afar, but those having their eyes inside, lying in a hollow, are able to see from afar because the movement is not scattered into the wide open space but goes straight.
οὐθὲν γὰρ διαφέρει τὸ λέγειν ὁρᾶν, ὥσπερ τινές φασι, τῷ τὴν ὄψιν ἐξιέναι (ἂν γὰρ μὴ ιἦ τι πρὸ τῶν ὀμμάτων, διασκεδαννυμένην ἀνάγκη ἐλάττω προσπίπτειν τοῖς ὁρωμένοις καὶ ἧττον τὰ πόρρωθεν ὁρᾶν), ἢ τὸ τῇ ἀπὸ τῶν ὁρωμένων κινήσει ὁρᾶν.
For it makes no difference to say that we see, as some say, by the sight going out (for if there is nothing in front of the eyes, it must, being scattered, fall less upon the things seen and see things from afar less), or by seeing by the movement from the things seen.
ὁμοίως γὰρ ἀνάγκη καὶ τὴν ὄψιν τῇ κινήσει ὁρᾶν.
For in the same way it is necessary for the sight also to see by the movement.
μάλιστα μὲν οὖν ἑωρᾶτο ἂν τὰ πόρρωθεν, εἰ ἀπὸ τῆς ὄψεως εὐθὺς συνεχὴς ἦν πρὸς τὸ ὁρώμενον οἷον αὐλός· οὐ γὰρ ἂν διελύετο ἡ κίνησις ἡ ἀπὸ τῶν ὁρατῶν·
Now, things from afar would be seen best if there were, as it were, a continuous tube straight from the sight to the object seen; for then the movement from the visible things would not be dissolved.
εἰ δὲ μή, ὅσῳπερ ἂν ἐπὶ πλέον ἀπέχῃ, τοσούτῳ ἀκριβέστερον τὰ πόρρωθεν ὁρᾶν ἀνάγκη.
Otherwise, by how much more it extends, by so much more accurately is it necessary to see things from afar.
καὶ τῆς μὲν τῶν ὀμμάτων διαφορᾶς ἔστωσαν αὗται αἱ αἰτίαι.
And let these be the causes of the difference of the eyes.