First Author: Y.Wong UK
Co Author(s): A. Khan
Purpose:
To theoretically show that it takes less 10% phenylephrine in comparison to 2.5% phenylephrine minim drops, to create a concentration to be given intracamerally to induce mydriasis.
As fewer minim drops of 10% phenylephrine are necessary, the conceal endothelium will be subjected to a lower concentration of toxic sodium bisulfite, a preservative contained in the minims.
Setting:
: Theory based
Methods:
Intracameral phenylephrine is now regularly used in cataract surgery for complicated cases such as floppy iris syndrome. 2.5% phenylephrine minims are routinely used and create a concentration which induces mydriasis. This theoretical review shows how less 10% phenylephrine minim needs to be used to achieve the same concentration. Reducing the number of drops would result in a lower sodium bisulphite concentration intracamerally, as this is the preservative used in phenylephrine minims. Sodium bisulfite is known to be toxic to the corneal endothelium inducing corneal oedema and a lower concentration would therefore reduce the risk of subsequent side effects.
Results:
Calculations show how less 10% phenylephrine in comparison to 2.5%, is required to create a solution with balanced salt solution to administer intracamerally :-
50mg of phenylephrine in 0.5ml = 10%
12.5mg of phenylephrine in 0.5ml = 2.5%
One drop from a minim = 0.05mls
Therefore
One drop of 10% phenylephrine = 5mg of phenylephrine
One drop of 2.5% phenylephrine = 1.25mg of phenylephrine
Common practise is to use 0.25 ml of 2.5% intracamerally diluted in 1.25ml BSS, which provides us with 6.25mg of intracameral phenylephrine. To achieve a similar concentration using 10% phenylephrine would require:-
Either 1 drop 10% phenylephrine = 5mg
2 drops of 10% phenylephrine = 10mg
This would contain less sodium bisulfite, as less of the phenylephrine and it’s preservative agent has been used to create a similar concentration.
Conclusions:
It requires less 10% phenylephrine minim in comparison to 2.5% phenylephrine minim to create a safe intracameral solution with BSS to induce mydriasis. By using less 10% phenylephrine the cornea is exposed to less toxic sodium bisulfite which is the preservative used in creating phenylephrine minims.
Financial Disclosure:
None
