Intra ocular pressure

Topical routes of drug administration are where the drug is applied directly to the site of action. Many medicines are applied directly for example, hydrocortisone can be rubbed into the skin to relieve a local area of inflammation. The anticholinesterase neostigmine is dropped directly onto the eye surface to relieve glaucoma, a condition characterised by raised intra-ocular pressure which if untreated can lead to blindness. 

Furthermore, by in vitro experiments, it has been verified that stereospecific activation of alprenoxime is organ-specific, occurring in the eye and not systemically. When administered locally to rabbits, marked decreases in intra-ocular pressure were observed, whereas oral administration elicited almost no cardiac effects. Such ketoximes represent promising chemical delivery systems in the treatment of glaucoma However, a major limitation is their poor stability in solution, seemingly due to hydrolysis of the oxime function. 

Calculations performed by Winter [35] showed that the increase in hydrostatic pressure (3-6 Torr) is within the physiological limits and should be well tolerated by the eye (normal intra-ocular pressure 20 Torr). 

All these parameters are very close to the requirements which a long-term ocular endotamponade has to fulfil. Also the in vivo tests in a rabbit eye model were extremely promising no emulsification, no changes in the vascular structure of the retina and no increase of the intra-ocular pressures. All negative side effects, seen with the monomeric FCLs, seemed to be eliminated. In addition, some additional advantages could be claimed reduced tissue penetration and the potential to dissolve drugs [44,45]. 

There are several types of -class CAs i.e., a-CA I-VII, reported in the literature, out of which the human carbonic anhydrase II (HCA II), the most extensively studied carbonic anhydrase, has an exceptionally high CO2 hydration rate and a wide tissue distribution 107). The HCA II comprises a single polypeptide chain with a molecular mass of 29.3 kDa and contains one catalytic zinc ion, coordinated to three histidine residues, His 94, His 96, and His 119. A tetrahedral coordination geometry around the metal center is completed with a water molecule, which forms a hydroxide ion with a pK value of 7.0 108). Quigley and co-workers 109,110) reported that the inhibition of the synthesis of HCO3 from CO2 and OH- reduces aqueous humor formation and lowers intra-ocular pressure, which is a major risk factor for primary open-angle glaucoma. 

Randall tried every conventional IOP [Intra-Ocular Pressure] medication. Some worked for a time, then diminished in effectiveness. Meanwhile, his ophthalmologist was perplexed by the wide fluctuations in his IOP readings. Randall couldn t bring himself to clear up the mystery. 

Today, physostigmine is used only rarely in medicine, as a miotic, which helps to reduce intra-ocular pressure in the glaucomic eye, and as an antidote following the intake of anticholinergic drugs (e.g., atropine and scopolamine). 

Dear GD, Hammerton M, Hatch DJ, Taylor D. Anaesthesia and intra-ocular pressure in young children. A study of three different techniques of anaesthesia. Anaesthesia 1987 42(3) 259-65. 

Feneck RO, Cook JH. Failure of diazepam to prevent the suxamethonium-induced rise in intra-ocular pressure. Anaesthesia 1983 38(2) 120-7. 

Grover VK, Lata K, Sharma S, Kaushik S, Gupta A. Efficacy of lignocaine in the suppression of the intra-ocular pressure response to suxamethonium and tracheal intubation. Anaesthesia 1989 44(l) 22-5. 

Edmondson L, Lindsay SL, Lanigan LP, Woods M, Chew HE. Intra-ocular pressure changes during rapid sequence induction of anaesthesia. A comparison between thiopentone and suxamethonium and thiopentone and atracurium. Anaesthesia 1988 43(12) 1005-10. 

L3. Langham, M. E., Aqueous humor and control of intra-ocular pressure. Physiol. Revs. 38, 215-242 (1958). 

It is used chiefly as a miotic. The eonstrietion of pupil commences within 10 minutes of application and the effect lasts up to 12 hours. It is also employed to decrease intra-ocular pressure in glaucoma. The salieylate is eomparatively less deliqueseent than the sulphate. The drug is invariably recommended for marginal comeal ulcers. It also finds its seldom use for atony of the urinary bladder. 

It is an osmotic diuretic with a low renal threshold. It is also administered to maintain the output of urine during surgical procedures. It is also recommended to decrease intra-ocular pressure in acute glaucoma. 

Acute angle-closure glaucoma developed rapidly in eight patients given nebulised ipratropium and salbutamol. Increased intra-ocular pressure has been reported in others, including one patient using an ipratropium metered-dose inhaler with nebulised salbutamol. 

In clinical studies the Oeuserl system has been shown to lower intra-ocular pressure, the main (and sight threatening) symptom of glaucoma, for periods up to one week (a.47). Furthermore, there were fewer side effects associated with this system and patient compliance was improved in comparison with the conventional pilocarpine eye drop formulation. One disadvantage of the Ocusert system was the discomfort to some patients and potential retention problems within the eye (a.43). 

If the same test for intra-ocular pressure change is performed on a sample of individuals with open angle hypertensive glaucoma, a trimodal distribution of phenotypes is also obtained but the frequency of the P P genotype is much lower than in a randomly selected population. 

New efforts were directed to use this material in novel ophthalmic drug delivery platforms recent reports in scientific literature propose the SH as solid bio-adhesivedrug delivery system. Crosslinked SH films loaded with timolol maleate were successfully used to reduce intra ocular pressure in normotensive rabbits, prolonging the hypotensive effect for longer than commercial timolol maleate eye drops [35]. 

In spite of all the work that has been done so far, the mechanism that brings about the glaucoma is still not properly understood. There is some evidence that it may be due to disturbance of a hormone secreted by the hypothalamus, possibly one of the prostaglandins, which regulates the intra-ocular pressure (Dyke 1978). 

Sympathomimetics are used to produce mydriasis for ophthalmoscopic evaluation mydriasis is not maximal, as with the anticholinergic mydriatics, but especially in younger patients sympathomimetic mydriasis proves quite effective and causes little or no reduction in accommodation. Sympathomimetic agents are also used as vasoconstrictors in surgical procedures, for symptomatic relief or allergic reactions and hyperaemia of the conjunctiva, and to lower intra-ocular pressure in glaucoma. 

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