“…Nevertheless, resistance to the development of glaucoma demonstrated by some individuals with ocular hypertension and the apparent occurrence of glaucoma in rare individuals with normal or slightly above the normal IOP (normal-tension glaucoma) shows that IOP is not the only significant factor for the disease. Tolerance to a certain IOP contributes to individual variation in the disease, and other factors such as increased ocular peripheral vascular resistance, reduction of blood flow to the optic nerve, the action of excitotoxins, and depletion of neurotrophins in the retinal ganglion cells can interfere, increasing predisposition to glaucoma or triggering it (Marigo et al, 2001). Several reports implicate genetic factors in the etiology of glaucoma; the condition is usually seen in related individuals and specific ethnic groups, often associated with consanguinity in affected families (Sarfarazi et al, 1995).…”