What Factors causing short-term changes in intra-ocular pressure
1) Arterial blood pressure
2) Systemic venous pressure (SVP)
3) Mechanical pressure
4) Plasma osmolarity: Hyper-osmolarity due to mannitol makes intra-ocular pressure lower.
5) Blood pH : Metabolic acidosis by carbonic anhydrase inhibitors like acetazolamode reduces intra-ocular pressure.
6) Diurnal variation in intra-ocular pressure:
- Normal 5 mm Hg
- >8 mm of Hg - glaucoma
- 5 to 8 mm of Hg - glaucoma suspect
Normal peak in early morning and lowest in evening.
7) Seasonal variation
8) Systemic hyperthermia
9) Effect of general anaesthesia on intra-ocular pressure: Type of anaesthesia has role, so must be kept in mind while measuring inua- ocular pressure under GA. specially in children with congenital glaucoma.
In general, once the patient is under the effect of general anaesthesia: intra-ocular pressure is reduced.
10) Effects of drugs on intra-ocular pressure:
a) Alcohol, morphine products, lower etc.: intra-ocular pressure,
b) Steroids, caffeine, tobacco, LSD, etc.: increase intra-ocular pressure.
11) Blockage of the circulation of the aqueous -at pupil or at angle of anterior chamber: increase intra-ocular pressure.