A compound of Formula I for use in a method of treating ocular hypertension or glaucoma in a mammal, wherein the dashed lines indicate the presence or absence of a bond, the hatched wedges indicate the α (down) configuration, and the solid triangles indicate the β (up) configuration; B is a single, double, or triple covalent bond; n is 0-6; X is CH 2, S or O; Y is any pharmaceutically acceptable salt of CO 2 H, or CO 2 R, CONR 2, CONHCH 2 CH 2 OH, CON(CH 2 CH 2 OH) 2, CH 2 OR, P 2, CONRSO 2 R, SONR 2, or R is H, C 1-6 alkyl or C 2-6 alkenyl; R 2 and R 3 are C 1-6 linear alkyl which may be the same or different, and may be bonded to each other such that they form a ring incorporating the carbon to which they are commonly attached; R 4 is hydrogen, R, C(=O)R, or any group that is easily removed under physiological conditions such that R 4 is effectively hydrogen; R 5 is hydrogen or R; and R 6 is i) hydrogen; ii) a linear or branched hydrocarbon containing between 1 and 8 carbon atoms, which may contain one or more double or triple bonds, or oxygen or halogen derivatives of said hydrocarbon, wherein 1-3 carbon or hydrogen atoms may be substituted by O or a halogen; or iii) aryloxy, heteroaryloxy, C 3-8 cycloalkyloxy, C 3-8 cycloalkyl, C 6-10 aryl or C 3-10 heteroaryl, wherein one or more carbons is substituted with N, O, or S; and which may contain one or more substituents selected from the group consisting of halogen, trihalomethyl, cyano, nitro, amino, hydroxy, C 6-10 aryl, C 3-10 heteroaryl, aryloxy, heteroaryloxy, C 1-6 alkyl, OR, SR, and SO 2 R. wherein the dashed lines indicate the presence or absence of a bond, the hatched wedges indicate the α (down) configuration, and the solid triangles indicate the β (up) configuration; B is a single, double, or triple covalent bond; n is 0-6; X is CH 2, S or O; Y is any pharmaceutically acceptable salt of CO 2 H, or CO 2 R, CONR 2, CONHCH 2 CH 2 OH, CON(CH 2 CH 2 OH) 2, CH 2 OR, P 2, CONRSO 2 R, SONR 2, or R is H, C 1-6 alkyl or C 2-6 alkenyl; R 2 and R 3 are C 1-6 linear alkyl which may be the same or different, and may be bonded to each other such that they form a ring incorporating the carbon to which they are commonly attached; R 4 is hydrogen, R, C(=O)R, or any group that is easily removed under physiological conditions such that R 4 is effectively hydrogen; R 5 is hydrogen or R; and R 6 is i) hydrogen; ii) a linear or branched hydrocarbon containing between 1 and 8 carbon atoms, which may contain one or more double or triple bonds, or oxygen or halogen derivatives of said hydrocarbon, wherein 1-3 carbon or hydrogen atoms may be substituted by O or a halogen; or iii) aryloxy, heteroaryloxy, C 3-8 cycloalkyloxy, C 3-8 cycloalkyl, C 6-10 aryl or C 3-10 heteroaryl, wherein one or more carbons is substituted with N, O, or S; and which may contain one or more substituents selected from the group consisting of halogen, trihalomethyl, cyano, nitro, amino, hydroxy, C 6-10 aryl, C 3-10 heteroaryl, aryloxy, heteroaryloxy, C 1-6 alkyl, OR, SR, and SO 2 R. i) hydrogen; ii) a linear or branched hydrocarbon containing between 1 and 8 carbon atoms, which may contain one or more double or triple bonds, or oxygen or halogen derivatives of said hydrocarbon, wherein 1-3 carbon or hydrogen atoms may be substituted by O or a halogen; or iii) aryloxy, heteroaryloxy, C 3-8 cycloalkyloxy, C 3-8 cycloalkyl, C 6-10 aryl or C 3-10 heteroaryl, wherein one or more carbons is substituted with N, O, or S; and which may contain one or more substituents selected from the group consisting of halogen, trihalomethyl, cyano, nitro, amino, hydroxy, C 6-10 aryl, C 3-10 heteroaryl, aryloxy, heteroaryloxy, C 1-6 alkyl, OR, SR, and SO 2 R.