True about intra ocular pressure

(Increased in advancing age) (208-210-Khurana 4th)Intraocular pressure Normal IOP varies between 10 and 21 mm of Hg (mean 16 +- 2.5 mmHg)Various factors influencine TOP(a) Local factors(I) Rate of aqueous formation(II) Resistance of aqueous outflow (drainage) - Most important(III) Increased episcleral venous pressure - rise in IOP, the valsalva maneuver causes temporary increases(IV) Dilatation of pupil in narrow anterior chamber may cause rise of IOP.(b) General factors1. Heredity - It influences IOP by multifactorial modes2 **Age - The mean IOP increases after the age of 40 years, possibly due to reduced facility of aqueous outflow.3. **Sex - IOP is equal between the sexes in age 20-40 years. In older age groups increases in mean IOP with age is greater in female.4. **Diurnal variations of IOP - Usually there is tendancy of higher IOP in the morning and lower in the evening. This has been related to diurnal variation in the level of plasma cortisol5. **Postural variations - IOP increases when changing from the sitting to the supine positions6. Blood pressure -As such it does not have longterm effect on IOP. However, prevalence of glaucoma is marginally more in hypertensive than the normotensive.7. osmotic pressure of blood- An increase in plasma osmolarity as occurs after IV - mannitol, oral glycerol or in patients with uraemia) is associated with a fall in IOP, while a reduction in plasma osmolarity (as occurs with water drinking provocative test) is associated with rise in IOP.8. General anaesthetics and many other drugs also influence IOP e.g. alcohol lowers IOP, tobacco, smoking, caffeine and steroids may cause rise in IOP. In addition there are many antiglaucoma drugs which lower IOP.