Bechoros 6:2-3

Bechoros 6:2

Blemishes of the eye that permit slaughtering a firstborn animal: if an eyelid is pierced, defective or slit; cataracts; if it's tevalul (explained momentarily); a fleshy outgrowth in the form of a snail or a snake partially covering the pupil; a round protrusion. Tevalul means that the sclera (the white part of the eye) breaks through the iris and into the pupil. The pupil breaking through into the sclera is not a blemish because things that affect the sclera are not considered blemishes.

Bechoros 6:3

White spots or water in the eye are blemishes when they are permanent. White spots are considered permanent at 80 days; Rabbi Chaninah ben Antigonos says that the animal must be examined three times in 80 days. Water in the eye is considered permanent if the animal ate both fresh and dry fodder from rain-watered fields without recovering. (The fresh fodder is its food in Adar/Nisan and the dry fodder is its food in Ellul/Tishrei.) If it ate fresh and dry fodder from irrigated fields, or if it ate dry fodder followed by fresh fodder, it is not diagnosed as a permanent blemish. This cannot be determined until the animal eats the dry fodder after the fresh.