Ashtangasamgraha 32.6

32.6

tattu lekhanaṃ ropaṇaṃ snehanaṃ prasādanamiti caturvidhaṃ bhavati |

tatrāmlādibhī rasaiḥ pañcabhiḥ śuklārmādiṣu lekhanam ||

tadyathā |

karkaṭakaṃ vakraṃ sthuṭitaṃ vellitamasthicchallikāśvakarṇaṃ piccitaṃ dāritaṃ cūrṇitamatipātitaṃ śeṣitaṃ majjānugatamiti ||

That collyrium is of four kinds: scarifying (lekhana), healing (ropaṇa), oleating (snehana), and soothing (prasādana).
There, scarifying is done with the five tastes beginning with sour, in pterygium (arma) on the sclera and the like.
Namely:
crab-like, crooked, cracked, spiralled, splintered bone, horse-ear shaped, flattened, torn, pulverized, completely broken off, residual, and entered into the marrow.