In Chapter 6 of Tractate Bechoros, Mishnah 2, we move on to the topic of eye blemishes, which is the subject of two mishnayos. To understand the halachos before us, we must first note four parts of the eye's anatomy that are relevant to our matter.
Four Parts in the Anatomy of the Eye:
Halavan - the eyeball, the white part of it (in medical terms: the sclera). The mishnah calls it "the white," and in practice, no blemish occurs in it by itself.
Hasira - the iris, the colored part at the front of the eye (for someone with blue eyes - the blue part), the circle surrounding the center of the eye.
Hashachor - the pupil, the black dot in the center of the iris. In fact, it is merely an opening through which light enters, and its size is adjusted by the iris, which opens and closes and regulates its aperture.
Ris shel ayin - the skin surrounding the eyeball, which is the eyelid.
Blemishes of the Eyelid:
The mishnah says: "Ris shel ayin shenikav, shenifgam, shenisdak" - an eyelid that was punctured, notched, or split. We have three situations before us:
"Shenikav" - a hole was made in the eyelid.
"Shenifgam" - a piece is missing from it, like a sort of triangle that was cut out of the eyelid.
"Shenisdak" - the eyelid is split: nothing is missing from it, but it is cracked like one cut it with scissors.
In all of these, we are dealing with a permanent blemish that will not heal, and based on it, the bechor can be slaughtered outside the Temple courtyard.
"Harei be'einav dak":
The literal meaning of the word "dak" is something extremely thin, referring to a thin layer - which is commonly translated as a cataract: a sort of white protein membrane found on the lens of the eye, over the eye in the place of the pupil. As a rule, it seems that any whiteness appearing at the front of the eye poses a problem, and even other phenomena such as a pterygium will raise a similar difficulty. However, we must admit that it is not sufficiently clear how to translate these various terms precisely into the terminology of modern ophthalmology.
"Tevalul" - a mixing of colors:
The word "balul" means something mixed, from the word belilah - mixing. "Tevalul," therefore, is a mixture: a leakage of the black into the white or of the white into the black. The problem is with the white leaking into the black, meaning that part of the pupil is affected and a white color is seen in it.
"Chilazon, nachash, ve'einav":
"Chilazon nachash" - literally a snail and a snake, referring to white matter that enters the pupil in a snail-like shape and leaves a snake-like color, as explained by the halachic authorities. Here too, the exact identification is unclear.
"Ve'einav" - a round, grape-like growth on the surface of the eye, adjacent to the pupil.
These too are blemishes that invalidate a bechor.
The Mishnah's Definition of Tevallul:
The Mishnah asks: "Ve'eizehu tevallul?" - What is this mixing of colors being discussed? It answers: "Lavan haposek basira venichnas bashachor" - The white breaks through the sira, which is the iris, the colored part of the eye, and reaches the black inside; this is the blemish. However, "Bashachor venichnas balavan - eino mum" - in the opposite situation, where the black leaks outward into the white of the eye, this is not considered a blemish, "She'ein mumin balavan" - since whatever occurs in the white of the eye is completely irrelevant to the laws of a blemished animal.
In summary: In this Mishnah, we learned about the eye blemishes derived from its four parts - the white, the sira, the black, and the eyelid. The blemishes of the eyelid are punctured, flawed, and split, all of which are permanent blemishes that permit the bechor to be slaughtered outside the Temple courtyard. We also learned about "dak", "chilazon nachash", and "einav", as well as the definition of "tevallul": white breaking into the black is a blemish, whereas black entering the white is not a blemish, as there are no blemishes in the white.
In the next Mishnah, we will continue to discuss blemishes of the eye.