Other techniques to correct myopia include photorefractive keratectomy (PRK), radial keratomy (**RK**), laser epithelial keratomileusis (LASEK), intraocular lens implants and intrastromal corneal rings.

In obtaining the minor Aik in the form of a determinant we erased certain rows and columns, and we would have erased in an exactly similar manner had we been forming the determinant associated with A2:8, since the deleting lines intersect **rk** in two pairs of points.

In the latter case the sign is determined by -I raised to the same power as before, with the exception that Tux., replaces Tusk; but if one of these numbers be even the other must be uneven; hence A ik = - Aisï¿½ **rk** Moreover aik a,, aikarsAik +aisarkAis Aik, **rk** aik ars rs where the determinant factor is giyen by the four points in which the deleting lines intersect.

Along the line of flow x'A'P'J', >L =m, u=a'e-**rk**/"n, and from x' to 41.

M-**rk** - - Dreio.

Are intersected by the lines **RK**, RM, RN, we have SA/AX = TP/PQ = SP/PQ, since the angle PST = angle PTS.